Bulletin No 57 (Low Res) - SJS Resource Management
Transcription
Bulletin No 57 (Low Res) - SJS Resource Management
BALI 2013 East Asia: Geology, Exploration Technologies and Mines non-corporate Sponsors MEMR EMD Geological Survey Indonesia EXTENDED ABSTRACTS An Australian Institute of Geoscientists symposium organised in conjunction with Geoscientists Symposia 27-29 May 2013 bali, indonesia Sponsors Volume compiled by Julian Vearncombe Bulletin No. 57 - 2013 East Asia: Geology, Exploration Technologies and Mines - Extended Abstracts © Australian Institute of Geoscientists This booklet is copyright. All rights reserved. No part of this publication may be reproduced or stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior permission in writing of the copyright owners. Bulletin number 57 ISBN 1 876118 42 3 ISSN 0812 60 89 DISCLAIMER The Organising Committee sought to obtain a broad coverage of this topic. Every effort was made to minimise amendments in content of the resultant abstracts. Abstracts including references have been reproduced as submitted with changes restricted to typographic, punctuation and layout only. The opinions and statements within the individual papers comprising the Bulletin reflect solely the viewpoint of their authors, and are not necessarily shared by the Organising Committee of the Australian Institute of Geoscientists. Short quotations from the text of this publication and copies of maps, figures, tables etc (excluding any subject to pre-existing copyright) may be used in scientific articles, exploration reports and similar works provided that the source is acknowledged and subject to the proviso that any excerpt used, especially in a company prospectus, Stock Exchange report or similar must be strictly fair and balanced. Other than for the purposes of research or study the whole work must not be reproduced without the permission in writing of the Australian Institute of Geoscientists. ORGANiSING COMMITTEE • Julian Vearncombe (SJS Resource Management) • Jocelyn Thomson (Geoscientists Symposia & AIG) • Bill Hewitt (PT PZC Services, Jakarta} • Sandy Moyle (Goldminex Resources, Melbourne and Port Moresby) • Priyo Pribadi (Samindo Resources, Jakarta) • Wayne Spilsbury (Geoduck, Perth) Typesetting Joanne Hamilton, e-type design [email protected] East Asia: Geology, Exploration Technologies and Mines Thank you to our sponsors: non-corporate Sponsors MEMR EMD Geological Survey Indonesia Sponsors East Asia: Geology, Exploration Technologies and Mines Thank you to our trade booths and supporters: Contents Author title Satriya Alrizki, Rusiana Permana Investigation of a High Sulfidation Epithermal Cu-Au Deposits Using Induced Polarization And Magnetic Method in Batang Asai, Jambi 1 Mike Andrews The Exploration, Discovery and Development of the Way Linggo Epithermal Gold-Silver Mine in Southern Sumatra 3 Malcolm G. Baillie The Ingredients of Successful Exploration 5 Kelvin Brown New Exploration Technologies 6 Rowena Duckworth, Kevin Blake Petrology and Electron Microprobe Analyses in Target Generation and Metallurgy 7 KEYNOTE: M. Elias Nickel Laterites in SE Asia – Geology, Technology and Economics: Finding the Balance 9 Robert G. Ellis, Barry de Wet, Ian N. Macleod Inversion of Magnetic Data from Remanent and Induced Sources 12 R. H. Findlay, S. Meffre The Liamu Complex of the Papuan Peninsula; regional significance for the tectono-thermal history and discovery within the Papuan Peninsula, PNG 17 Mark Gabbitus From Exploration to Extraction 18 KEYNOTE: Steve L. Garwin Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific 19 Helen Gibson, John Sumpton, Des FitzGerald, Ray Seikel 3D Modelling of geology and gravity data: Summary Workflows for Minerals Exploration 24 Matthew R. Greentree, Gavin Chan Chinese Minerals Exploration Methods and Philosophy: Implications for Out-bound Investment 27 KEYNOTE: Graeme Hancock Realising the Mineral Potential of Mongolia 29 KEYNOTE: Craig J. R. Hart, Richard J. Goldfarb A Framework for China’s Gold Exploration and Endowment Page 30 Dedy Hendrawan, Gayuh ND Putranto The Tombulilato Copper Gold Project in Sulawesi, Indonesia ‘Facing the Challenges and Opportunities’ 32 T. Hoschke, S. Schmeider, S. Kepli Geophysics of the Elang Cu-Au Porphyry Deposit, Indonesia, and Comparison with Other Cu-Au Porphyry Systems 34 J. M. A. Hronsky Controls on High-grade Au Ore-shoots: Towards a New Paradigm 36 KEYNOTE: David Isles Ramping-up Exploration Value from Aeromagnetic Surveys – More Geological Input Needed! 39 Hashari Kamaruddin, Hartono, Ciputra Cu-Au Porphyry System of Atlantis Prospect, Papua Province: A Preliminary Report 42 poster: Imants Kavalieris, Khashgerel BatErdene Formation of Advanced Argillic Zones 43 David Lawie Sorting the Signal From the Noise 44 Contents Author title Page Evgenia Lebedeva, Andrew Riley Biogeochemistry and Partial Digest Techniques in Mineral Exploration – a Brief Review 46 poster: Sony Malik, Ferdian Haryadi, Gita Srikandi Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency 48 Adi Maryono, Rachel Harrison Porphyry Copper-Gold Mineralization Styles along the Eastern Sunda Magmatic Arc, Indonesia 58 D. Menzies, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick, G. Morehari, B. Tekeve, B. Alupian, J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter, P. Golias The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration Zonation, Surface Geochemical Expression and Paragenesis 60 Paul Merriner Case Study: Discovery and Geology of the Kham Thong Lai Copper-Gold Deposit, Lao PDR 64 KEYNOTE: AHG Mitchell, Myint Thein Htay The Magmatic Arc and the Slate Belt: Copper-gold and Tin-tungsten and Gold Metallotects in Myanmar 66 Chris J. Muller, Kieran Harrington, Hugh McCullough, Lindsay W. Bandy Mineralisation Potential of the Kulu-Fulleborn Trend (Whiteman Range), New Britain Island, Papua New Guinea 68 Yulia Nazimova, Gregory Ryan Alluvial and Bedrock Platinum, East Asia 71 A. H. (Tony) Osman The History of Coal Development in Indonesia 73 Rod Paterson Interpolating Assays and Physical Properties in Folded and Faulted Layered Geology 74 Rusiana Permana, Sufian Nur Hikmat, Yosafat P. Simanjuntak, Eratmadji, Bronto Sutopo Porphyry Cu-Au Occurrences in Batulicin Area, Batangasai, Jambi Province, Indonesia 76 C. Querubin, S. Walters, M. Papio, W. Satiyawan The Pani Gold Project: Geology and Mineralization 77 Neal Reynolds Tectonics and Metallogeny of Mainland Southeast Asia – Framework for New Discovery Opportunities 78 M. P. Roberts, R. A. Armstrong Age and O, Hf Isotope Systematics of the Yandera Porphyry Rocks Constraints on Magma Sources, Crystallisation History and Crustal Evolution 80 Stephen Sugden Field Portable XRF – Good Techniques to Avoid Bad and Ugly Analyses 83 Erric Sukmawan,Yosafat Palty Yudhistira Simanjuntak, Wanda Ilham Dani, Rusiana Permana, Bronto Sutopo A Lithocap in The Bujang Prospect, Jambi Province: Related or not Related to the Porphyry Cu – Au Mineralisation System 85 poster: Adi Sulaksono, Muhammad A. Luthan, and Putu A. Andhira Hydrothermal Alteration Study In Tertiary Volcanism Ayah Area, Southern Central Java 87 Geoff Taylor, Greg Corbett, Grace Cumming Cirianiu Epithermal Au, Vanua Levu, Fiji 89 Andrew J. Vigar, Ian Taylor, Greg MacDonald Resource Estimation for the Aurukun Bauxite Deposit 91 Brad Whisson Developments in Microwave Digestion for Geochemical Analysis 92 1 l Investigation of a High Sulfidation Epithermal Cu-Au Deposits Using Induced Polarization and Magnetic Method in Batang Asai, Jambi Satriya Alrizki, Rusiana Permana Investigation of a High Sulfidation Epithermal Cu-Au Deposits Using Induced Polarization and Magnetic Method in Batang Asai, Jambi Satriya Alrizki1 and Rusiana Permana2 A detail geological investigation has been carried out in Batang Asai area, Jambi province for prospecting the indication of gold mineralization in the area. Geological investigation has resulted in several mineralization prospect areas such as Batulicin prospect, Kayuaro prospect, Hulu Banyak ikan prospect and Gunung Bujang prospect. Especially in Gunung Bujang prospect, the mineralization consists of covellite, chalcocite, and enargite in advanced argilic alteration zone (pyrophyllite-alunite-dickitekaolinite±diaspore) and also siliceous (vuggy-massive quartz). Based on the evaluation of geological data mineral alteration in Gunung Bujang prospect, it is concluded that the mineralization type was Deep HSE (High Sulphidation Epithermal) with alteration found in the form of quartz alunite, phyropilite, paragonite, and muscovite. Induced Polarization (IP) surveys were conducted by PT.ANTAM Unit Geomin in the late 2012. Approximately 9 lines for a total 11 kilometres of 25 m dipole-dipole was read with 100 metres between lines over Gunung Bujang prospect. The Induced Polarization (IP) data was inverted using a 2D algorithm by Earth Imager AGI to produce a block model and section of resistivity and chargeability. From the IP result it shows significant anomaly correlation between high resistivity from over a thousand ohm meter and high chargeability for a hundred msec, in about 180 m of depth penetration. A detailed magnetic data was also collected during that year, using 5 m spacing between each data point collected, the magnetic survey covered 16,5 kilometres over Gunung Bujang prospect. The alteration at Gunung Bujang prospect is not magnetic destructive, we could still find a magnetic characteristic mineral such as magnetite,hematite,pyrite over the outcrop in Gunung Bujang. The magnetic data was filtered by using Oasis Montaj Geosoft software to produce RTP (reduce to pole) Map with 25 meters upward continuation. The overlay result between RTP (reduce to pole) map and distribution of alteration by Short Wavelength Infra Red (SWIR) shows that the minerals pyrophylite, dickite, alunite, kaolinite (lithocap) and other minerals such as muscovite, diaspore etc are localized at moderate to high zone of magnetic anomalies, the same characteristis is found 1. PT. Antam (Persero) Tbk.- Unit Geomin, Jl. Pemuda No.1, Jakarta Timur. Telp. 021-4755380, Fax. 021-4759860 Corresponding author: [email protected]; [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 2 l Investigation of a High Sulfidation Epithermal Cu-Au Deposits Using Induced Polarization and Magnetic Method in Batang Asai, Jambi in the prospects of Elang Prospect in Sumbawa through measurement of airborne magnetic survey. Airborne RTP magnetic anomaly pattern in Elang prospect at Sumbawa, a type of porphyry Cu-Au mineralization is almost similar to its pattern with the Gunung Bujang prospect Groundmagnetic RTP anomalies. From Gunung Bujang magnetic anomalies we could find bull’s eye anomalies constituted from the RTP Map (high magnetic surrounded by low magnetic). Even more interesting is the presence of two high magnetic patterns, one pattern flanking magnetic low. In addition, to identify potential areas of alteration, the magnetic data contains a significant amount of information that may reveal geological and structural Satriya Alrizki, Rusiana Permana features simultaneously with the Induced Polarization (IP) data to reveal the distribution and localized conductive minerals that related to Deep HSE mineralization deposit in the subsurface. References Tim Eksplorasi Emas Jambi, Laporan Eksplorasi Emas dmp - Semester II tahun 2012, Daerah Batulicin dan Gunung Bujang, Kabupaten Merangin, Propinsi Jambi, Unit-Geomin PT ANTAM (persero) Tbk, 2012 Tim Eksplorasi Geofisika Jambi, Laporan Penyelidikan Geofisika Metoda IP dan Magnetik - Semester II tahun 2012, Daerah Gunung Bujang, Kabupaten Merangin, Propinsi Jambi, Unit-Geomin PT ANTAM (persero) Tbk, 2012 East Asia: Geology, Exploration Technologies and Mines - Bali 2013 3 l The Exploration, Discovery and Development of the Way Linggo Epithermal Gold-Silver Mine in Southern Sumatra MIKE ANDREWS The Exploration, Discovery and Development of the Way Linggo Epithermal Gold-Silver Mine in Southern Sumatra MIKE ANDREWS1 The Way Linggo gold-silver mine was successfully brought into production in August 2010 by Kingsrose Mining (the project’s 85% major shareholder). This marked the culmination of some 26 years of exploration by seven different companies over a regional tenement which originally covered approximately 9,500 sq km. The Way Linggo mine is situated centrally in the 4th Generation PT Natarang Mining Contract of Work area which currently is 100 sq km bounded on the north and westerly sides by the Bukit Barisan National Park and to the east by tracts of unprospective recent volcanics. The tenement is focused on the northern truncation of the Semangka Graben which western boundary is the Trans Sumatra Fault and the East side is bounded by the Semangka Fault. The Trans Sumatra Fault is the major long lived strike slip fault running the length of the Western portion of Sumatra which has had a profound regional influence on the localisation of volcanicity and related epithermal and porphyry mineralisation on that island. These two large fault systems converge at the northern end of this graben and have generated a complex dilational zone characterised with active pull-apart basins on scales of 10’s kms down to 100’s metres and dilational splays. At Way Linggo underground mining is mainly focussed on the high grade North Vein a low sulphidation epithermal vein system comprising two en-echelon ore bodies which are texturally distinct, the A Orebody dominated by a white Quartz-Adularia-Clay assemblage and B Orebody characterised by a Quartz- Calcite-Green SmectiteChlorite? assemblage. These zones average approximately 5 m in width and appear to be joined by a link vein system. The ore bodies at Way Linggo are best developed where hosted in a porphyritic dacite intrusive host and appear to loose grade tenor where the bounding structure enters andesitic tuffs along strike to the north. Kingsrose Mining has commissioned a 140,000 tpa Merill-Crowe processing plant fed from the Way Linggo underground mine from two adit accesses, an external 700 feet railed skipway to haul ore from the main haulage levels and an internal shaft. The initial JORC compliant resource on mine start up was 669,000 tonnes @ 8.44 Au g/t, 129 Ag g/t. Mining is by traditional narrow vein generally hand held methods, haulage underground by electric locos. The Contract of Work was signed in December 1986 with Musswellbrook Energy and Minerals as the foreign partner who selected the area covering most of the outcrops of Miocene andesitic volcanics in Lampung province. They undertook a number of regional geochemical drainage sampling programmes over the entire 9,500 sq km and identified the drainages in the Way Linggo area as lower order geochemical anomalies, no follow up was carried out. In 1989 Ashton Mining took over the project and followed up the higher order anomalies elsewhere in the tenement without success. By chance during a brief follow up traverse in drainages some 15 km downstream of the mine two pieces of banded quartz vein float were sampled however these gave low gold grades (2.3 and 3.4 Au g/t), the project geologist ( Joel Ivey) recognised the interesting epithermal textures and instigated further follow up which lead to the discovery of an extensive epithermal float train in the drainage 2.5 km to the east of Way Linggo, the Semung Kecil prospect. Soil surveys identified a well defined gold, arsenic, silver c-horizon soil anomaly coincident with some surface outcrops of siliceous sinter, however trenching an exploration adit and subsequent drilling failed to confirm significant mineralisation at Semung kecil (It does still remain an inticing target). During mapping of the peripheral areas west of Semung Kecil narrow epithermal veins were found exposed in streams to draining into the Way Linggo waterfall, a soil grid was undertaken in this area to the south of the current mine which confirmed a 450 m by 250 m gold, arsenic soil anomaly and trenching identified numerous narrow 10 cm to 1 m epithermal gold bearing veins but generally of low grade. A 1 m wide vein outcrop exposed due to low river levels river indicated that the soil grid should be extended over the northern part of the prospect, although no coherent anomalies were detected, a single spot high of 6 g/t Au in C-Horizon soil was trenched uncovering the subcrop of the North Vein. Ashton Mining and its spin off Aurora Gold refocused elsewhere in Indonesia, notably on the development of the Mount Muro Mine in Kalimatan and in 1994 the Project 1. Southern Arc Minerals Inc. (Formerly Director, Kingsrose Mining Ltd), Graha Sentana, Jl. Buncit Raya, Jakarta 12760, Indonesia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 4 l The Exploration, Discovery and Development of the Way Linggo Epithermal Gold-Silver Mine in Southern Sumatra was taken over by Meekatharra Minerals which instigated discovery drilling. Meekatharra Minerals focus was to prove up enough ore to sustain a 30,000 oz per annum high grade gold project so work focussed on completing a feasibility study on the project, this was completed in 1996. However the Bre-X scam and collapsing gold price saw Meekatharra, renamed AuIron Energy refocusing on its Australian coal and iron ore assets at the time many companies were exiting Indonesia. A private consortium Advance Concept Holdings Ltd acquired the project from AuIron in 2000 and commenced limited underground development to access the North Vein orebody to enable level development to confirm grades predicted from drilling. Face sampling revealed significantly higher grades than the drill core. The ACH consortium successfully floated Kingsrose Mining on the ASX in December 2007 and in February 2009 Kingsrose acquired the project and focussed on rapid project construction. For the Year ending June 2012 Kingsrose reported a production of 37,650 oz Au and 432,754 oz Ag from Way Linggo at one of the lowest cash operating costs per ounce. MIKE ANDREWS Kingsrose has undertaken a very extensive exploration programme of the entire tenement, including using BLEG geochemistry, airborne magnetics and radiometrics, and CSAMT coupled with aggressive diamond drilling campaigns. They have been rewarded with the discovery of their second mine Talang Santo which is currently under construction. Kingsrose currently reported a JORC resource of 485,869 oz Au at grades of 6.91 Au g/t and 45 Ag g/t (all categories) in their 2012 Annual report. The Way Linggo project is a good example of the need for a persistence of exploration effort, requirement for good geological observation, not to miss the right signs and blindly follow the assays and corporate commitment to aggressive drilling campaigns. The prospectivity northern extent of the Semangka graben has been highlighted by the discovery the Way Linggo mine but its potential as a new mineral district has only been identified by the aggressive exploration and drilling by Kingsrose Mining. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 5 l The Ingredients of Successful Exploration Malcolm G. Baillie The Ingredients of Successful Exploration Malcolm G. Baillie1 While the primary skill of the Exploration Manager is his geological knowhow, this alone is not enough to guarantee success. There are a mass of non-technical issues which he must manage to avoid failure, even when a good resource is present. Broadly, these issues relate to good communication with corporate management, dealing with the environmental and social issues specific to the project location, relationships with Government authorities and operating in accordance with the regulatory regime. This presentation looks at the nature of these non-technical factors for Indonesian projects, and how, in many cases they can take up more of the Exploration Manager’s time than the exploration program itself. The difficulties in successfully managing these issues have resulted in the abandonment of more than one project in Indonesia, and have contributed to the very low level of grass roots exploration now taking place. Some of the reasons for this are examined, including what is believed to be a significant lack of understanding of the nature of exploration by the public in general, and by regulators specifically. One of the first responsibilities of the Exploration Manager is to communicate frankly and in a timely fashion with his corporate management. This is where the finance originates. The head office of this organisation is usually based offshore and its management may not be familiar with the issues encountered. It has to report to shareholders, who are even less familiar with the local issues, and confidence in the exploration team is rapidly lost if shocks are encountered. There is more than one recent case which illustrates this problem. Environmental issues are generally minimal during exploration, but local communities generally expect all exploration to result in a mine, so it is important to consider the potential impact at an early stage and to communicate with local people and improve their understanding. The establishment of a sound relationship with the local community from the very beginning is critical. This cannot be done without thorough profiling of the local community and the leaders and should precede any field work. Once trust with the local community is lost, it is very difficult to recover. Employment policies, land acquisition and dealing with illegal mining all require a cooperative approach. Dealing with Government authorities is another critical matter. Regional, Provincial and Central Government are all involved. Each considers its role as the most important, and they may not have a common view on all issues. In recent months, many new regulations have been issued. Some of these have a distinctly negative effect on exploration, and some are not clear. It is essential that the Exploration Manager fully understands the nature of these regulations and communicates their impact on the project to corporate management. While few amongst the mining sector dispute the Government’s policy to seek an appropriate return from mining operations, it seems likely that the regulations actually put into place will have the effect of strangling the industry. New mining operations are essential to maintain the industry, and these are entirely dependent on successful exploration. Exploration and mining are two very different activities. Exploration involves high risk with less than one in a hundred projects leading to a mine. Mining is a business, subject to feasibility before commitment like any other. Quite different companies seek involvement in the two sectors – junior exploration companies dominating the exploration field. Yet the regulations seek to cover both activities as if there is an inevitable follow on. It is more realistic to view exploration as normally leading to the creation of new geological data and not to a mine. The Government should seek its return from mines and encourage exploration companies to spend their precious funds efficiently on finding them. The necessary support could be provided within the existing Mining Law if the difference between exploration and mining was understood. Approvals for exploration activities (e.g. Forestry Permits) could be simplified and streamlined to avoid the unnecessary costs of delay, and if the need for exploration to be spread over many projects was recognised. In summary, there are many factors which contribute to a successful exploration program. Some are technical, and some are non-technical. All need to be assessed before starting field work and all need to be continuously monitored. Excessive difficulties associated with any could be the basis for not commencing field work or curtailing it once started. Exploration funds are limited and have to be directed where there is the best chance of success. 1. Chairman, Forum for Exploration and Mining Development, Indonesia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 6 l New Exploration Technologies Kelvin Brown New Exploration Technologies Kelvin Brown1 Data Acquisition Past: A brief look back at how we gathered geological data during the mineral exploration drilling process. Present: How data is currently gathered, the improvements made to date and the shortcomings that still exist. Future: A look at where we need to take this process by utilising new technologies & methods in a way that increases production, reduces costs and improves the data availability. Data Management How do we manage this data that is expensive to acquire? Is it secure? Which data do we need sooner? Over the recent decade our ability to generate vast quantities of data has significantly increased but has our capability to manage this data increased with it? Here we will look at state of the art systems that can help us to identify the important information needed to make the best decisions and how we can get this information quickly to the stakeholders. 1. Imdex, 8 Pitino Court, Osborne Park, Western Australia 6017 Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 7 l Petrology and Electron Microprobe Analyses in Target Generation and Metallurgy Rowena Duckworth, Kevin Blake Petrology and Electron Microprobe Analyses in Target Generation and Metallurgy Rowena Duckworth1 and Kevin Blake2 Optical microscopy is a traditional technique for characterising rocks and describing the mineral textures and parageneses. However, it is a technique that is not used as widely as it used to be, despite its ability to provide relatively factual information about rocks reasonably quickly and cheaply. Electron Microprobe Analysis (EPMA) is a more modern analytical technique that utilises X-ray detection methods to provide definitive mineral chemistries and element identification. Both of these techniques can be used on regular polished thin sections (no extra thickness of thin section is required for microprobe work). These two techniques combined can, therefore, divulge abundant information about core, chip and outcrop samples that is useful for target generation and, down the track, metallurgy and mineral processing. One of the most important uses of optical microscopy is to complement/ contradict the hand specimen descriptions, especially those generated during routine core logging. Submitting one or two samples for petrology from each lithology encountered is recommended, as logging descriptions can prove to be unreliable, and should always be groundtruthed before mineralisation models and target generation plans are developed. An example of this is a suite of rocks logged as amphibolites that systematically failed to contain any amphibole when observed using transmitted light microscopy. This type of hand specimen mis-identification is common, and can lead to incorrect mineralisation models. As well as determining the major, minor and accessory minerals in a rock sample optical microscopy can identify: • Primary mineralogy • Metamorphic minerals, textures, metamorphic facies, and the degree and sequence of ductile or brittle deformation events • Alteration mineralogies and facies • Vein and selvage mineralogy • Sequence of events (paragenesis) including the timing of ore mineralising events: did the ore minerals come in early or late? EPMA back scattered electron image showing dark grey pyrite grains that have been variably brecciated and replaced by several telluride phases (with differing brightness). At this scale, using reflected light microscopy there may be just a hint of another phase present in the pyrite and with the naked eye it may not be apparent at all. Microscopic description of rocks can also help with the refinement of stratigraphy and structure, the identification of geological and hydrothermal processes and assist with ore grade vectoring from near miss drill holes. Staining techniques are largely not used these days due to modern OHS regulations as they utilise hydrofluoric acid. Hence microprobe analyses can be helpful in determining carbonate chemistries and feldspar chemistries, which often cannot be determined optically. Electron microprobe analysis can additionally provide crucial information with respect to the location of elements of interest: e.g. gold? Gold can occur as native gold, bonded with other elements to form a mineral, e.g. sulphosalts, as inclusions within a mineral or bound up in the lattice of another mineral phase. Often assays will indicate the presence of significant gold, but in hand specimen and even under the optical microscope, it is difficult/ 1. Gnomic Exploration Services, Townsville, Qld 4810 Corresponding author: [email protected] 2 Advanced Analytical Centre, James Cook University, Townsville, Qld 4814 East Asia: Geology, Exploration Technologies and Mines - Bali 2013 8 l Petrology and Electron Microprobe Analyses in Target Generation and Metallurgy impossible to locate the gold. EPMA imaging and energy dispersive (EDS) chemical analysis can usually resolve this problem. The back scattered electron image below is from a deposit where the company was not sure from the assay data whether the gold was occurring as free gold or as telluride complexes. Microprobe analysis showed that there was native gold as well as a range of telluride complexes including, gold, gold-silver, silver-gold, iron and mercury tellurides. This highlights the need to understand the correlation between assay data and the mineralogy. For quantitative mineral analysis, EDS or wavelength dispersive analysis (WDS) can be used depending on the detection limits of the elements in question. WDS analysis Rowena Duckworth, Kevin Blake has a better resolution but is more time consuming, as it requires calibration for each element to be analysed (major plus minor elements of choice, F, Cl, Cu, Co, Te, Ag etc.) and each analysis can take 3-4 minutes depending on the elements being measured. However, the results are definitive and can be extremely useful as exploration vectors. Quantifying and then mapping the amount of a particular trace element in a particular mineral is a powerful mineralisation vectoring method. Microprobe analyses can also be useful in the processing stage of mining in order to identify any contaminants, adverse or beneficial, which may affect the final mineral concentrate. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l keynote 9 Nickel Laterites in SE Asia – Geology, Technology and Economics: Finding the Balance M. Elias Nickel Laterites in SE Asia – Geology, Technology and Economics: Finding the Balance M. Elias1 This presentation reviews the nature and genesis of nickel laterite mineralisation, and describes the relationship between deposit characteristics (both geological and nongeological) and the successful development of lateritic deposits as commercial nickel producers. The importance of nickel laterites lies in their huge resource base, which could potentially provide a much greater share of global nickel production than their current level compared to nickel from sulphides. Nature of nickel laterite mineralisation Most of the world’s terrestrial nickel resources are hosted in nickel laterites. These are products of intense weathering in humid climatic conditions of Mg-rich or ultramafic rocks which have primary Ni contents of 0.2-0.4%. The process of lateritisation involves the breakdown of primary minerals and release of their chemical components into groundwater, the leaching of mobile components, the residual concentration of immobile or insoluble components, and the formation of new minerals which are stable in the weathering environment. The combined effects of these processes is to produce a vertical succession of horizons of differing chemistry and mineralogy (the laterite profile), the overall structure of which is governed by the differential mobility of the elements in the weathering zone. The detailed structure of the profile varies greatly, and in any one place is the result of the dynamic interplay of climatic and geological factors such as topography, drainage, tectonics, structure and parent rock lithology. Nickel (and typically cobalt) can be enriched to ore grade in parts of the profile by being incorporated into the structure of the newly formed stable minerals or into the alteration products of primary minerals. Figure 1 is a diagrammatic representation of a typical laterite profile developed in a tropical environment. At the base of the profile, initial stages of weathering produces saprolite, in which the unweathered rock fabric is preserved, although most of the original minerals may have been altered. As weathering proceeds, Mg and Si are leached until in the upper part of the profile only insoluble Fe oxides remain. This is referred to informally as limonite. Despite the complexity and interplay of controls, there are a number of broad features of the laterite profile that are Figure 1. Schematic laterite profile developed on ultramafic rock in a tropical climate, showing indicative chemical compositions in wt%. Parts of the laterite profile which are viable sources of feed for the respective extraction methods are shown. common to most examples, and it is possible to describe the range of laterite types formed over ultramafic rocks on a deposit scale in terms of three main categories on the basis of the dominant Ni-bearing mineralogy developed in the profile: Oxide laterites: comprise largely Fe oxyhydroxides and oxides (mainly goethite) in the upper part of the profile, overlying altered or fresh bedrock; Clay laterites: comprise largely smectitic clays in the upper part of the profile, and Silicate laterites: comprise hydrated Mg-Ni silicates (serpentine, garnierite) occurring deeper in the profile, which may be overlain by oxide laterites. Although the detailed morphology and composition of the deposits can vary greatly on a small scale (tens of metres), deposit scale and regional scale controls result in broad consistencies in deposit characteristics over wider areas. For example, lateritisation of tectonically uplifted ultramafic massifs which host most of the nickel laterites in New Caledonia has produced thick silicate laterite deposits, and physical erosion has removed most of the oxide laterites. A more subdued topography in the Philippines has resulted in greater preservation of the oxide zone and generally less 1. Principal Consultant – Nickel, CSA Global Pty Ltd, West Perth Corresponding author: ??? East Asia: Geology, Exploration Technologies and Mines - Bali 2013 10 l Nickel Laterites in SE Asia – Geology, Technology and Economics: Finding the Balance intense alteration in the silicate laterite zone. Clay laterites are not represented in the SE Asia-Pacific region as the climatic and tectonic controls required for their formation are absent. Global resources of nickel laterites are estimated to contain in excess of 150 million tonnes of nickel. Of this total, over 50% is found in New Caledonia, Indonesia, the Philippines and Papua New Guinea. That such a large proportion of global resources is found in a relatively small area is due to the favourable combination of tectonic and climatic factors. Tectonically active zones typical of the region are often associated with oceanic or continental plate boundaries and collision zones, where thrust faulting has obducted slabs of upper mantle peridotites and associated rocks forming ophiolite complexes with extensive areas of exposure at surface. Tectonic processes (i.e. uplift) play a large part in influencing the type of nickel laterite deposits formed. Exploration and resource delineation Exploration for Ni laterites does not present significant technical problems. The occurrence and distribution of ultramafic rocks is well known in most, if not all, deeply weathered terrains. They can be readily and more precisely delineated at regional to local scales by airborne magnetic surveys, which can also be used to outline lithological variation, stratigraphy and favourable structures. Within appropriate areas, preliminary geomorphological, regolith-landform and structural maps can be prepared from aerial photography, a variety of remote sensing techniques and magnetic surveys to determine the most prospective sites for potential Ni accumulation. Follow-up by inspection, field mapping and drilling are used to outline the potential resource. Diamond core drilling is the most common method of sampling for resource delineation. Initial drilling on a widespaced grid is followed by progressive infill drilling in areas of better results. Ni laterite deposits show great variation in the distribution of Ni and other elements, profile thickness and other characteristics over short distances. Advanced exploration for accurate estimation of resources and reserves and for reliable mine planning therefore relies on having an adequate drilling density; generally a 25-50 m grid is used. Subsequently, precise grade control and careful blending of mined ore categories are required to minimize variation in the composition of plant feed and thus optimize plant operating conditions. Grade control commonly requires drilling or sampling on grids of 5-10 m. M. Elias • Sample assaying – the most commonly used methods employ XRF on either fused glass disks or pressed powder pellets. • Bulk density and moisture determinations – the porous nature and high moisture contents of laterites make these difficult. Mineral processing and metal extraction About 50% of primary nickel produced globally is sourced from lateritic ores. Methods currently in use on a commercial scale to extract nickel from laterites comprise three main processing routes: • Smelting to produce ferro-nickel or matte, including nickel pig-iron (NPI), • Caron process (reduction roast – ammoniacal leach), and • Leaching using sulphuric acid, under atmospheric or high pressure conditions. Due to the requirements of each process and the wide range in chemical and mineralogical composition in the laterite profile, each of these processes is only suited to a part of the profile. No commercially applied process has yet been developed to economically treat the entire profile, and this remains the “holy grail” of laterite processing. Thus any processing method has to be carefully matched with the mineralogical and compositional range of the deposit it is intended to treat. Figure 1 shows the applicability of each process within the profile. Each of the processes has drivers which influence not only production cost but also non-economic factors such as plant location. Some of these include: • Smelting – highly energy intensive, requires cheap power; ore chemistry (Si:Mg ratio) is critical; no benefit from by-product credits; product well suited to stainless steel production. • Caron process – highly energy intensive; high capital cost; poor by-product (Co) recovery. • Acid leaching – sensitive to acid consumption and sulphur cost; high capital cost; technology risk; good Ni and Co recovery; tailings storage and effluent disposal issues in tropical environments. Because the processing method is essentially determined by the type of deposit, it follows that infrastructure and plant location should be capable of supporting its operation. Other factors to be aware of in resource delineation programs and mine planning include: Ingredients of a successful laterite project • Drilling should extend at least two to three metres into bedrock to ensure that the entire profile has been intersected. History has shown that new nickel laterite development projects have a very patchy record of success. Commercial development of nickel laterite projects is a high risk undertaking due to the high capital costs involved and the need for the application of the highest standards of technology and engineering. However, there are a number • Core recovery – laterites often comprise a mixture of hard rock boulders in a soft matrix. HQ-sized core is generally required to ensure adequate sample recovery. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 11 l Nickel Laterites in SE Asia – Geology, Technology and Economics: Finding the Balance of natural attributes of nickel laterite deposits that, if they applied in new projects, would improve their chances of successful development and becoming profitable operations. It helps to have a quality orebody in terms of size, grade, consistency, and ore and overburden thickness, and the SE Asian region is well endowed in this respect. Nevertheless, successful projects clearly also require a favourable combination of geological, mineralogical and mining factors, technical and engineering factors related to the process flowsheet, infrastructure-related factors and environmental considerations. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 M. Elias 12 l Inversion of Magnetic Data from Remanent and Induced Sources ROBERT G. ELLIS, Barry de Wet, Ian N. Macleod Inversion of Magnetic Data from Remanent and Induced Sources ROBERT G. ELLIS 1, Barry de Wet2 and Ian N. Macleod1 Summary Magnetic field data are of fundamental importance in many areas of geophysical exploration with 3D voxel inversion being a common aid to their interpretation. In the majority of voxel based inversions it is assumed that the magnetic response arises entirely from magnetic induction. However, in the last decade, several studies have found that remanent magnetization is far more prevalent than previously thought. Our experience with numerous minerals exploration projects confirms that the presence of non-induced magnetization is the rule rather than the exception in base metals exploration. In this work we show that failure to accommodate for remanent magnetization in 3D voxel-based inversion can lead to misleading interpretations. We present a technique we call Magnetization Vector Inversion (MVI), which incorporates both remanent and induced magnetization without prior knowledge of the direction or strength of remanent magnetization. We demonstrate our inversion using model studies and field data. Successful application to numerous minerals exploration surveys confirms that incorporating remanent magnetization is essential for the correct interpretation of magnetic field data. Introduction The utility of magnetic field data in many areas of geophysical exploration is well-known as is the application of 3D voxel inversion to aid in magnetic data interpretation (for example, Li and Oldenburg 1996, Pilkington, M., 1997, Silva et al. 2000, Zhdanov and Portniaguine 2002, to cite just a few). In the majority of voxel based inversions it is assumed that the magnetic response arises entirely from magnetic induction. However, in the last decade, studies have found that remanent magnetization is far more prevalent than previously thought (McEnroe et al. 2009) and affects crustal rocks as well as zones of mineralization. Unfortunately, remanent magnetization can seriously distort inversion based on the assumption that the source is only induced magnetization. The severity of the distortion is due to the highly non-unique nature of potential field inversion making it extraordinarily easy for a potential field inversion to produce a seemingly plausible model which agrees satisfactorily with the observed data, even when a fundamental assumption in the inversion is flawed. Several authors have reported progress toward magnetic data inversions including remanent effects (for example, Shearer and Li 2004, Kubota and Uchiyama 2005, Lelièvre and Oldenburg 2009). In this work we report further progress in this direction with a technique we call Magnetization Vector Inversion (MVI), which incorporates both remanent and induced magnetization without prior knowledge of the direction or strength of remanent magnetization. In the following sections, we extend conventional scalar susceptibility inversion to a magnetization vector inversion, that is, we allow the inversion to solve for the source magnetization amplitude and direction. While this increases the number of variables in the inversion we will show by example that the same regularization principles that allow compact targets to be resolved in highly unconstrained scalar susceptibility inversion also apply in vector inversion. Perhaps our most significant finding is that MVI, or more generally, inversion including all forms of magnetization, significantly improves the interpretation of the majority of minerals based magnetic field inversions. Unfortunately, the surprising degree of improvement in interpretability cannot be adequately presented in a paper and can only be verified by direct experience. Consequently, while we have applied MVI to a large number of magnetic field surveys and find the results to be significantly superior to conventional scalar based inversion, in this paper we are forced to limit our attention to a synthetic case and field data from the Cu-Au Osborne deposit located approximately 195km SE of Mount Isa, in Western Queensland, Australia. Method and Results Let us begin with the very general assumption that the magnetic properties of the earth can be represented by a volume magnetization, M(r) (Telford et al. 1990). We make 1. Geosoft Inc. Suite 810, 207 Queens Quay West, Toronto, ON, Canada Robert. Corresponding author: [email protected] 2. Ivanhoe Australia Ltd., Level 13, 484 St Kilda Road Melbourne, VIC, 3004, Australia East Asia: Geology, Exploration Technologies and Mines - Bali 2013 13 l Inversion of Magnetic Data from Remanent and Induced Sources no assumptions about whether source of the magnetization is induced, remanent, or otherwise. From magnetostatics, the magnetic field B at point rj resulting from a volume V containing magnetization, M(r), is given by This expression shows directly that the magnetization vector M(r) is the natural parameter for inversion. This is a crucial observation. If the volume V consists of a collection of N sub-volumes vk each of constant magnetization mk then This defines the forward problem: given a set of sources mk (k =1,..,N) then Bj is the predicted magnetic field anomaly at points, rj (j=1,..,M). Note that the coordinate index is summed over indicating that we are free to choose the most computationally convenient internal coordinate system. It also suggests that a coordinate invariant quantity, such as the amplitude, M(r) = lM(r)l will be most robustly determined from the data. ROBERT G. ELLIS, Barry de Wet, Ian N. Macleod Example - Buried Prism Although the buried prism model is far too simplistic to have exploration significance, it does make an excellent pedagogical example, so we follow tradition and begin by considering the inversion of simulated TMI data over a buried prism with magnetization vector M perpendicular to the earth field. The model consists a cube with side length 40m buried with a depth to top of 20m and a magnetization vector in the EW direction, (My = 0, Mz = 0) as shown in Figure 1. Simulated TMI data are shown in Figure 2 for Earth field with inclination 90° and amplitude 24000 nT. Cardinal directions have been chosen only for simplicity of explanation; any directions could be chosen with equivalent results. Also for simplicity, the data were simulated at 20m constant clearance and on a regular 8m grid. Inverting the TMI data in Figure 2 yields the model shown in Figure 3 which should be compared to the true model shown in Figure 1. There is some variability in the magnetization direction but the predominant direction is clearly EW, in agreement with the true model. For conciseness, we will represent Eq (2) simply as The vector magnetization inverse problem is defined as solving for m given B subject to an appropriate regularization condition. Although there are many choices for the regularization (see for example, Zhdanov 2002), we choose without loss of generality, the familiar Tikohonov minimum gradient regularizer. The inverse problem becomes solving for m in, where in the first line, the total objective function f is the sum of a data term fD and a model term fM with a Tikohonov regularization parameter, l . The second line defines the data objective function in terms of the data equation (3) and the error associated with each data point. ej. The third line gives the model objective function in terms of the gradient of the model ∂g m and the amplitude of the model, with weighting terms as required, wgw0 . The fourth line indicates that the Tikohonv regularization parameter l is chosen based on a satisfactory fit to the data in a chi-squared sense, XT2. In addition, other constraints, such as upper and lower bounds, can be placed on m as appropriate to the specific exploration problem. Figure 1.The buried prism model with magnetization vector orientation (Easterly) shown by the green cones. Side=100m Figure 2. The TMI data simulated over the magnetization vector model shown in Figure 1. The axes are in metres. Vector magnetization models in 3D are difficult to interpret directly in all the but the simplest cases. In real-world exploration we need some simpler derived scalars which highlight the important information in the vector model. As suggested by Eq(1), the most robust and meaningful scalar East Asia: Geology, Exploration Technologies and Mines - Bali 2013 14 l Inversion of Magnetic Data from Remanent and Induced Sources ROBERT G. ELLIS, Barry de Wet, Ian N. Macleod Figure 3: The MVI recovered model for comparison with Figure 1. The magnetization vector orientation shown by the green cones. is the amplitude of the vector magnetization and this should be the primary quantity used in interpretation. However, since the magnetization vector direction is the earth field direction for induced sources, it is tempting to attempt to use the directional information recovered in MVI to generate scalars related to the earth field direction. There are many possibilities but we have found that three useful derived scalars for exploration are: the amplitude of the magnetization, the earth field projection of the magnetization, and the amplitude of the perpendicular-toearth-field components of the magnetization. In exploration problems, the amplitude is robust by being independent on of any assumptions regarding the earth field, while the amplitude perpendicular is an approximate indicator of non-induced magnetization. To support our findings, these three derived scalars are shown in Figure 4b, c, d for an East-West slice through the model volume bisecting the target in the true model. In exploration situations it is convenient to present MVI output normalized by the amplitude of the earth’s magnetic intensity in the area of interest. That is, our results are displayed as where is the amplitude of the earth’s magnetic intensity in the area of interest. By using this normalization in an area of purely induced magnetization, the numerical values returned by MVI inversion will be directly comparable to those of scalar susceptibility inversion, in our case in SI. For completeness, and to show the contrast between MVI and conventional scalar inversion, Figure 5b shows the equivalent section through a model produced by an inversion which assumes only induced magnetization. As should be expected, the recovered model using scalar inversion is a very poor representation of the true model, which in real-world exploration ultimately adds significant confusion to the interpretation process. This simple prism example demonstrates the power of magnetization vector inversion and its advantage over scalar susceptibility inversion in cases where the magnetization vector direction deviates from the earth field direction. We argue that this situation predominates in real-world Figure 4: (a) A cross section through the true model, (b) the recovered amplitude of the magnetization vector, (c) the amplitude of the perpendicular-to-earth-field components of the magnetization, (d) the projection of the magnetization on to the earth field direction. The colour scales indicate the MVI magnetization in normalized to SI (see text). Figure 5: (a) A cross section through the true model, (b) the recovered scalar susceptibilty. The color bar shows the susceptibility magnitude in SI. exploration environments based on experience from many magnetic surveys, however this cannot be shown here. Example - Osborne The preceding pedagogical study of MVI on simulated data over a prism provides a solid basis for the much more important application of MVI to field data. As mentioned in the Introduction, it is hard to appreciate fully the impact on magnetic data interpretation by including non-induced magnetic sources. However, to motivate our assertion, we present typical results taken from TMI data collected over the Osborne deposit. The history of the Osborne mine is well described elsewhere, see for example, Rutherford et al. 2005. Briefly, significant Cu-Au mineralization beneath 30-50m of deeply weathered cover was confirmed in 1989. Intense drilling between 1990 and 1993 defined a total measured and indicated resource of 11.2 Mt at 3.51% Cu and 1.49 g/t Au. Exploration since 1995 has delineated high-grade primary mineralization dipping steeply East to some 1100 m vertical depth. As of 2001, total mined, un-mined and indicated resources are reported to be about 36 Mt and 1.1%Cu and 1 g/t Au East Asia: Geology, Exploration Technologies and Mines - Bali 2013 15 l Inversion of Magnetic Data from Remanent and Induced Sources ROBERT G. ELLIS, Barry de Wet, Ian N. Macleod (Tullemans et al. 2001). Current exploration is focussed on mapping the high- grade mineralization to greater depths and mapping similar structures in the surrounding area. The geophysics includes total magnetic intensity (TMI) data over the property, which is shown in Figure 6. The TMI data were acquired in 1997 flown at 40m clearance on 40m line spacing. Figure 7: An EW section through the recovered MVI model amplitude at the Osborne property with the now known mineralization shown in black. The color bar gives the normalized amplitude in SI. The axes are in metres. Figure 6: The observed TMI data acquired over the Osborne property. The axes are in metres. The color scale shows the TMI amplitude in nT. Magnetization Vector Inversion of the Osborne TMI data yields the magnetization vector amplitude earth model shown in Figure 7. Superimposed (in black) is the subsequently discovered mineralization from extensive drilling and underground mining. For comparison, Figure 8 shows the corresponding scalar susceptibility inversion. Comparing Figure 7 and Figure 8 shows that inverting for the magnetization vector provides a much better model for interpretation. The scalar inversion fails to represent reality in this case suggesting, most likely, that the scalar assumption is violated: a common occurrence in mineral exploration in our experience. In contrast the MVI model is consistent with the drilling results, and furthermore, indicates a steeply dipping volume on the Eastern flank. The strong near surface anomaly to the west of the dipping zone is known banded ironstone. Conclusions We have argued that remanent magnetization must be included in magnetic field data inversion in order to avoid seriously misleading interpretations. To support this argument we demonstrated the value of Magnetization Vector Inversion using model studies, and field data from the Osborne property. The degree of improvement afforded by using MVI in all areas of magnetic field data inversion may seem surprising, however recent advances in understanding remanent magnetism suggest that non-induced magnetization plays a far more important role than previously thought in the origin of magnetic anomalies. Successful application to numerous minerals exploration surveys confirms that incorporating Figure 8: The same section as in Figure 7 for the scalar model with drilling and mineralization in black. The color bar gives the susceptibility in SI. The axes are in metres. remanent magnetization is recommended for the correct interpretation of the majority of magnetic field data. Acknowledgements The authors would wish to thank Geosoft Inc. and Ivanhoe Australia Ltd. for permission to publish this work. References Butler, R. F., 1992, Paleomagnetism: magnetic domains to geologic terranes, Blackwell Scientific Publications. Kubota, R., and Uchiyama A., 2005, Three-dimensional magnetization vector inversion of a seamount, Earth Planets Space, 57, 691–699 Li, Y., and D. W. Oldenburg, 3-D inversion of magnetic data, Geophysics, 61, 1996, 394-408. Lelièvre, P. G., and Oldenburg, D. W., 2009, A 3D total magnetization inversion applicable when significant, complicated remanence is present, Geophysics, 74, L21-L30 McEnroe, S. A., Fabian, K., Robinson, P., Gaina, C., Brown, L., 2009, Crustal Magnetism, Lamellar Magnetism and Rocks that Remember, Elements, 5, 241-246. Pilkington, M., 1997, 3-D magnetic imaging using conjugate gradients, Geophysics, 62, 1132-1142. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 16 l Inversion of Magnetic Data from Remanent and Induced Sources Rutherford, N. F., Lawrance, L. M., and Sparks, G., 2005, Osborne Cu-Au Deposit, Clonclurry, North West Queensland, CRC LEME Report. Shearer, S., and Y. Li, 2004, 3D Inversion of magnetic total gradient data in the presence of remanent magnetization: 74th Annual Meeting, SEG, Technical Program, Expanded Abstracts, 23, 774-777. Silva, J. B. C., Medeiros, W. E., and Barbosa, V. C. F., 2001, Potentialfield inversion: Choosing the appropriate technique to solve a geologic problem, Geophysics, 66, 511 - 520. Telford, W. M., Geldart, L. P., Sherriff, R. E., and Keys, D. A., 1990, Applied Geophysics, Cambridge University Press. ROBERT G. ELLIS, Barry de Wet, Ian N. Macleod Tullemans, F. J., Agnew P., and Voulgaris, P., 2001, The Role of Geology and Exploration Within the Mining Cycle at the Osborne Mine, NW Queensland, in Monograph 23 - Mineral Resource and Ore Reserve Estimation - The AusIMM Guide to Good Practice, Australian Institute of Mining and Metallurgy, Melbourne, 157-168. Zdhanov, M. S., 2002, Geophysical Inverse Theory and Regularization Problems, Method in Geochemistry and Geophysics 36, Elsevier Science B.V., Amsterdam, The Netherlands. Zhdanov, M. S., and Portniaguine, O., 2002, 3-D magnetic inversion with data compression and image focusing, Geophysics, 67, 1532-1541 East Asia: Geology, Exploration Technologies and Mines - Bali 2013 17 l The Liamu Complex of the Papuan Peninsula; regional significance for the tectono-thermal history and discovery within the Papuan Peninsula, PNG R. H. Findlay, S. Meffre The Liamu Complex of the Papuan Peninsula; Regional Significance for the Tectono-thermal History and Discovery Within the Papuan Peninsula, PNG R. H. Findlay1 and S. Meffre2 Effective exploration in greenfields terrains requires proper delimitation of the regional geological and geochronological architecture of the broad target district to enable efficient vectoring into the target. Many greenfields areas, such as those in PNG and Asia, and indeed Australia, have been mapped only at the broad reconnaissance scales and their geochronological relationships are usually poorly understood. The Liamu Complex, in tenements held by Goldminex Resources Ltd in the Papuan Peninsula, provides a regionally important case study of discovery by careful attention to systematic geological mapping, allied to geomorphology, legacy geochemical data and geochronology. The Papuan Peninsula is known for its history of very small-scale alluvial gold and PGE mining, and generally unsuccessful exploration by industry. The region is underlain by obducted latest Cretaceous-Palaeocene oceanic basalts and ultramafic complexes extending for 250km (Papuan Ultramafic Belt), juxtaposed against low- to high-grade metasedimentary rocks of probable Cretaceous age to the south. Until recently the source of the gold in ground occupied by the Papuan Ultramafic Belt was most uncertain, despite reconnaissance geological mapping by PNG government geologists and first-pass regional geochemical surveys by industry. In 2009, reinterpretation of the 1:250 000PNG government geological maps, allied to geomorphological observations and legacy geochemical surveys in the Liamu River area of the Musa Valley, highlighted incompatibilities in the previous interpretation of the geology and led to systematic regional and detailed geological mapping that has identified a major 45 sq km plus intrusive and extrusive complex (Liamu Complex) containing Cu-Au porphyry indications and evidence for structurally controlled epithermal deposits. This mapping has also allowed focused and therefore costeffective geophysical surveys that appear to show that the complex may be as large as 75sq km. sparse prior K/Ar dating, confirms a very late Miocene to Pliocene thermal event in the Papuan Peninsula, one that was involved in production of potassic intrusive bodies and monzonite intruding the Papuan Ultramafic Complex along the length of the Papuan Peninsula. Rocks similar to those in Liamu Complex are reported in the legacy geochemical data, and geomorphological studies combined with brief helicopter-supported visits and float sampling in 2011 indicate the strong probability of several other such late Miocene-Pliocene intrusive systems along the Papuan Peninsula and within the Papuan Ultramafic Belt. These discoveries allow an integrated regional model for both Cu-Au porphyry/epithermal discovery in the Papuan Peninsula and also explain the prominent development of Ni-sulphide occurrences along major fault systems cutting the ultramafic rocks of the Papuan Ultramafic Belt. The geochronology, albeit one sample in addition to a very few prior K/Ar ages, confirms that in late Miocene and Pliocene times the Papuan Peninsula was host to the same regional, mineralising, tectono-thermal event that has hosted such deposits as Porgera (5.2Ma) and Tolukuma (4.6Ma), among the many others extending from the Wau-Bulolo goldfields of Morobe to Frieda River in the westernmost part of PNG. A recent geochronological study (U/Pb zircon) has yielded an age of 6Ma for the current drilled target in the Liamu Complex. Apart from the lithostratigraphic importance of this age, which demands that this part of the complex must be tilted by around 20 degrees, it, together with 1. Montagu Minerals Mapping Pty Ltd,44 Riawena Road, Tasmania 7018. Corresponding author: [email protected] 2. CODES, University of Tasmania, Sandy Bat, Hobart, Tasmania 7018 Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 18 l From Exploration to Extraction mark Gabbitus From Exploration to Extraction mark Gabbitus1 Technology is increasingly being asked to fill the skills shortage in mining. Geologists are being asked to do more in less time with less training and mentoring. Therefore it is essential that the software used during exploration, geological modelling, resource modelling and grade control is capable of quickly, accurately and auditably producing the results required by the end users of the model, engineers and miners. New technologies such as implicit modelling reduces the time spent by geologists building models and allows for the rapid generation of multiple block models for a project. Used alongside estimators of risk, such as conditional simulation, geologists can present best case to worst case scenarios for optimisation and scheduling that meets the growing demand of engineers and, perhaps more importantly, investors. Beyond feasibility studies and resource modelling it is also important that the grade control system used at a site is flexible, can be automated and is able to interface with the growing level of mining information available today for accurate reconciliation. Software companies are responding to these needs and this paper will detail how MineSight® has approached this challenge both through the software and the services provided to ensure that exploration and mining companies can progress from the first hole drilled to the last truck extracted in a single system. This single system approach to geology, engineering and mining ensures that the integrity of data is maintained throughout the mining value chain without the need for highly skilled users. 1. Regional Business Development Manager, MineSight Applications Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l keynote 19 Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific Steve L. Garwin Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific Steve L. Garwin Introduction Gold and copper deposits in Southeast Asia and the west Pacific occur largely in middle to late Cenozoic (25 to 1 Ma) magmatic arcs. The region contains more than 160 deposits, including porphyry, skarn, epithermal, volcanicassociated massive sulfide, disseminated sedimentary rock-hosted deposit and other mineralization styles. The combined past production and current resources of these deposits exceeds 15,000 tonnes of gold and 115 million tonnes of copper (Garwin et al., 2005). The majority of the gold and copper are contained in porphyry and epithermal deposits, many of which contain resources of more than five million ounces of gold (Figure 1). Miocene, Middle Miocene and the Plio-Pleistocene (Barley et al., 2002; Garwin et al., 2005). Hydrothermal systems were active for durations of < 100,000 years. Arc-continent collisions and the subduction of buoyant aseismic ridges Magmatic Arcs and Tectonic Setting Twenty major magmatic arcs and several less extensive arcs of Cenozoic age form a volcano-plutonic chain that extends >17,000 km from Japan in the northeast, through Taiwan, Philippines, Indonesia, Malaysian Borneo, and Papua New Guinea, to Myanmar in the northwest. The arcs are constructed on basement formed from continental and oceanic crust. The geometries of individual arc segments are complex and typically the product of subduction, locally involving polarity reversals, seamount subduction, obduction, arc-arc and arc-continent collisions, rifting, and transcurrent faulting. Most of the porphyry and epithermal deposits developed during episodes of plate reorganization and local variations in arc stress regimes during the Early Figure 1. Present-day tectonic features, major Cenozoic magmatic arcs and large porphyry and epithermal deposits of Southeast Asia and the west Pacific. Only deposits that contain more than five million ounces of gold are shown. Thick red lines with triangles are subduction zones and thick black lines are major strike-slip faults (modified from Hall, 2002 and Garwin et al., 2005). Digital topography and bathymetry models are from the United States National Geophysical Data Center. Indicated magmatic arcs and seafloor topographic features are described partially in the text of this abstract and comprehensively in Garwin et al. (2005). The locations of the magmatic arcs are modified from Hamilton (1979), Hutchison (1989), Yamada et al. (1990), Mitchell and Leach (1991), Carlile and Mitchell (1994), and Garwin et al. (2005). Several buoyant aseismic ridges and oceanic plateaux are being, or have been, subducted beneath overlying arcs, including the Palau-Kyushu Ridge in southwestern Japan, the Scarborough Seamounts in Luzon, the Ontong Java Plateau in Papua New Guinea – Solomon Islands, the Roo Rise near Sumbawa, and the Investigator Ridge in Sumatra. The subduction of each of these seamounts has led to the development of large porphyry and epithermal deposits in the region. The large deposits in medial New Guinea did not form above an active subduction zone but within uplifted regions in a fold- and thrust-belt in a convergent setting. 1. Independent Consultant and Adjunct Research Fellow, Centre for Exploration Targeting, School of Earth and Geographical Sciences, University of Western Australia, Nedlands, WA 6009, Australia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 20 l Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific vary the orientation of predominantly arc-orthogonal stress fields and induce episodic reactivation of crustal-scale fault systems in transpressional to transtensional settings. The distribution of porphyry and epithermal deposits reflects differences in structural- and tectonic-setting and composition of the crustal basement (Table 1; Sillitoe and Hedenquist, 2003; Garwin et al., 2005). Many of the deposits are spatially and temporally related to intrusions and volcanic centers in calc-alkaline to alkaline andesiticdacitic arcs. Porphyry, and high- and intermediatesulfidation epithermal deposits occur typically in contractional to neutral arc settings and are closely related to shallow intrusions, volcanic centers, and, locally, diatremes. Low-sulfidation epithermal systems are associated with intra-arc and backarc grabens and extensional settings that control bimodal basaltic-rhyolitic volcanism in Japan, calc-alkaline volcanism focused near dilational jogs in the Sumatra strike-slip fault system in Indonesia and K-alkaline magmatism in Papua New Guinea. Tectonic Stress-Regime Probable Causes Deformation Style Contraction Deposit Types Deposit Examples Subduction Slab Topology and Seamount Collisions The majority of the porphyry and epithermal deposits in the region lie above subduction slabs. However, the giant deposits in medial New Guinea (e.g., Grasberg, Ok Tedi and Porgera) lack an active subduction zone and are the product of collisional tectonics in a fold- and thrust-belt. Major changes in the dip of the subduction slabs define kink zones that plunge obliquely to nearly orthogonal to the local strike-direction of each slab. The origin of these slab kinks is, in part, related to the age and density of the crust that comprises the subduction slabs. Buoyant, aseismic oceanic ridges (seamounts) have collided with portions of the subduction zones in several localities (Figure 1). The seamounts consist of inactive, sea-floor spreading centers; leaky transform faults and ancient sea-floor volcanic fields. These seamount collisions enhance the coupling of Near-Neutral Extension arc-arc, arc-continent collision; buoyant seamount subduction; fast convergence and high OCR; subduction of young oceanic crust most common arc setting; shares similarities to contractional arc, but lacks major collisions and typically is characterized by slab rollback and episodes of arc-relaxation orogen-parallel folds, reverse faults and thrust belts; orogen-transverse strike-slip to oblique-slip faults orogen-parallel and orogenorogen-parallel normal faults and transverse strike-slip to oblique-slip grabens, intra-arc and backarc; faults; dilational jogs in strike-slip marginal basins fault systems Subduction slab rollback due to subduction of older oceanic crust or tearing of slab adjacent to buoyant ridge; slow convergence and low OCR calc-alkaline to K-alkaline andesitedacite tholeiitic to calc-alkaline bimodal basalt-rhyolite; K-alkaline mafic to intermediate rocks Plio-Pleistocene Medial New Guinea (CM) Plio-Pleistocene Luzon Central Cordillera (IA) Plio-Pleistocene Southern Ryukyu (Taiwan, CM) Pliocene Cotobato (CM?) Pliocene N. Sulawesi (IA) Pliocene NE Japan (CM) Neogene Sunda (CM to IA from W to E, mildly contractional between E. Java and W. Sumbawa) Plio-Pleistocene Philippines (IA) Early Miocene Central Kalimantan (CM) Middle Miocene NE Japan (backarc, CM) Pleistocene Ryuku (CM) Pleistocene Izu-Bonin (IA) Pleistocene Outer Melanesian (Tabar-Feni, IA) Au-rich Porphyry, Skarn, HS, IS Porphyry, HS, IS, (LS), DS Grasberg, Ok Tedi, Far South East Ertsberg, Wabu Lepanto, Chinkuashih Porgera pit, Victoria, Acupan-Itogon (Baguio) Tujuh Bukit, Batu Hijau, Elang and Tombulilato district Martabe, North Lanut, Nalesbitan Kelian, Toka Tindung, Placer Lebong Donok (dilatant jog in SFS) and Pongkor Mesel, Bau calc-alkaline to K-alkaline andesiteMagmatic Suite and dacite; diminished volcanic activity Style or volcanic gap Arc Examples Steve L. Garwin VMS, LS Kuroko deposits in Hokuroku district (tholeiitic) Hishikari (tholeiitic) and Ladolam? (K-alkaline) Table 1. Summary of tectonic regime, deformation, magmatism and mineralization in Cenozoic magmatic arcs of Southeast Asia and the west Pacific (modified from Garwin et al., 2005) Abbreviations: OCR - Rate of convergence orthogonal to magmatic arc; SFS - Sumatra Fault System. Arc settings: CM, continental margin setting; IA, oceanic island arc setting. Deposit styles: DS, disseminated sedimentary rock-hosted; HS, high-sulfidation epithermal; IS, intermediate-sulfidation epithermal; LS, low-sulfidation epithermal; VMS, volcanic-associated massive sulfide. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 21 l Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific Steve L. Garwin the subducting slab with the overriding arc crust, which increases the normal stress across this interface (Scholz and Small, 1997) and promotes uplift of the overlying arc (Garwin et al., 2005). Examples of seamount subduction that occur near zones of significant gold and copper mineralization in the region include the Palau-Kyushu Ridge near Kyushu in southern Japan (site of Hishikari, ~ 1 Ma); the Scarborough Seamounts in northern Luzon in the Philippines (Lepanto – Baguio, 1.5 to 0.7 Ma); the Roo Rise near eastern Java – western Sumbawa in Indonesia (Bukit Tujuh, Batu Hijau and Elang, ~ 4 to 2.7 Ma); and the Investigator Ridge near northern Sumatra in Indonesia (Martabe, ~ 3 Ma). Similar relationships between subducted seamounts and the location of arc-transverse, intrusion-related mineral belts are observed in the Central Andes (Sasso and Clark, 1998; Sillitoe, 1998; Kerrich et al., 2000). In the Southeast Asian collisional sites mentioned in the preceding paragraph, epithermal or porphyry deposits formed during a transition in local stress-regime that developed as a response to seamount subduction (Garwin et al., 2005). Northern Luzon provides one of the most dramatic examples of the relationship between the effects of the topology of the subduction slab on the uplift of the overlying arc and gold-copper deposit development. The slab beneath the Luzon arc dips steeply eastward (60 to 80°) beneath the Manila Trench, underlying two parallel island arcs that extend between Taiwan and Luzon (Figure 2). The accretion of the extinct spreading center of the South China Sea (Scarborough Seamounts) at the Manila Trench at about 5 to 3 Ma stalled subduction, and magmatism ceased in the western arc (Yang et al., 1996; Bautista et al., 2001). The dip of the Luzon slab flattens to about 30° at the site of collision (16-18° N), which partly underlies uplifted portions of the fore-arc basin known as the Stewart Bank and Vigan High (Hayes and Lewis, 1984; Pautot and Rangin, 1989). The Baguio-Mankayan region, where Miocene coralline limestone has been uplifted to > 1500 m above sea-level, lies near the southern margin of the subducted seamounts, above an abrupt change in slab-dip from ~ 30° to the north to > 60° to the south. The subducting slab is suggested to have torn along the trace of the Scarborough Seamounts at about 2 Ma, which led to the upwelling of underlying asthenosphere through the torn slab and a migration in magmatism towards the east (Yang et al., 1996; Bautista et al., 2001). The timing of this second magmatic pulse correlates with the formation of porphyry and epithermal deposits in the Mankayan district (1.4 to 1.15 Ma; Hedenquist et al., 1998, 2001) and the Baguio region (~1.5 Ma and 0.65 Ma; Sillitoe, 1989; Cooke et al., 1996). In contrast to northern Luzon and other arc-trench settings, the relationship of subduction to alkaline magmatism and related Plio-Pleistocene mineralization in medial New Guinea is not clear. Southerly-directed subduction beneath the New Guinea Trench is too young to explain this magmatic-hydrothermal event, and subduction related to the Figure 2. Tectonic framework of the Luzon arc and elements relevant to the eastward subduction of the South China Sea plate (from Garwin et al., 2005). The Scarborough Seamounts (SS), the extinct spreading center of the South China Sea, subducts below Luzon. A buoyant oceanic plateau, to the north of this aseismic ridge, is also inferred to have accreted to the base of the Luzon Central Cordillera (LCC; Bautista et al., 2001). This accretionary process has led to the uplift of the Stewart Bank (SB) and Vigan High (VH), which segment the fore arc to form the North Luzon Trough (NLT) and West Luzon Trough (WLT). The Baguio and Mankayan districts underwent extensive uplift in the Plio-Pleistocene and lie along the subducted trace of the Scarborough Seamounts (Knittel et al., 1995). Two parallel island arcs extend between Luzon and Taiwan. In the Luzon Central Cordillera and towards the north, volcanic activity was focused in the western arc (WVC) from the Miocene to middle Pliocene (~ 4-3 Ma) and migrated to the eastern arc (EVC) in the late Pliocene (~ 2 Ma), which remains active to the present. PSF = Philippine fault system; COB = margins of the South China Sea plate. The relative motion between the Philippine Sea plate and Eurasia (86 km/m.y.) is from McCaffrey (1996). calc-alkaline Maramuni arc ceased by ~ 10 Ma. However, the spatial and temporal correlation between large porphyry and epithermal deposits (e.g., Porgera ~ 6 Ma, Grasberg ~ 3 Ma and Ok Tedi ~ 1 Ma) and the southward progression of fold-and-thrust belt deformation (Davies, 1991) suggests that crustal thickening and block uplift played a critical role in metallogenesis. Rapid convergence between New Guinea and the Caroline plate in the Late Miocene caused compression throughout the island and uplift of the Papuan East Asia: Geology, Exploration Technologies and Mines - Bali 2013 22 l Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific fold belt (Hill et al., 2002). In the Pliocene, compressional stresses were reduced and transpression characterized the New Guinea margin, which is inferred to have facilitated dilation about the intersections between frontal thrusts and northeasterly-trending, orogen-transverse faults (Hill et al., 2002). These dilatant zones served as the loci for the emplacement of mantle-derived, potassium-rich magmas and the generation of large hydrothermal systems at shallow crustal levels. Crustal-scale, Arc-transverse Faults and Lineaments Arc-transverse fault zones are inferred to control the distribution of many of the intrusion-related deposits in medial New Guinea, Luzon, Sunda-Banda, and in other magmatic arcs in the region (Corbett and Leach, 1998; Garwin et al., 2005). Similar cross-arc distributions of deposits exists in the central Andes, where arc-transverse mineral belts coincide with faults, fracture zones and lineaments defined by deflections in regional structural grain and geological discontinuities (Skewes and Stern, 1995; Sasso and Clark, 1998; Sillitoe, 1998; Richards et al., 2001). In Southeast Asia, arc-transverse oblique- to strike-slip faults extend on the order of 100 to 400 km across many of the magmatic arcs, and indicate arc-parallel extension on the order of about 3 mm/yr locally (e.g., near Timor, Indonesia; McCaffrey, 1988). Crustal-scale lineaments, inferred from regional geology, digital topography, satellite gravity, bathymetry, and satellite imagery, extend at angles of about 45° to 70° across the Indonesian arcs. Many of these lineaments coincide with clusters of shallow (< 30 km depth) earthquake hypocenters along major faults in the arc and backarc, and coincide with segments of varying earthquake activity in the underlying Benioff zone (figure 8 in Garwin et al., 2005). These arc-transverse fault- and fracture-zones are inferred to extend towards the base of the crust and create dilatant channels for hydrothermal fluids and the efficient release of metal-bearing volatiles exsolved from melts at high levels in the overlying arc (e.g., < 4 km beneath paleosurface). District-scale Structural Controls The major controls to large porphyry and epithermal deposits and districts in the region typically include second- and higher-order fault systems that lie adjacent to arc-transverse fault- or fracture-zones that have localized Neogene to Pleistocene magmatism and locally, sedimentation. The most prolific intrusion-related districts are characterized by areas of uplift and exhumation in regional-scale, compressional to near-neutral stress-regimes that have experienced variations or inversions in the local stress-fields. In contrast, several of the low-sulfidation epithermal systems typically lack a direct connection to causal intrusions and occur in extensional settings but may also be associated with stress-regime inversions. Steve L. Garwin The local structural settings that promote the heat- and fluid-flow necessary to produce large porphyry and epithermal deposits in the region include: 1) dilatant zones in long-lived fault systems; 2) structural highs, domes, anticlines or horst-blocks; and 3) the margins of pre- to syn-mineralization plutonic complexes, horst-block margins and competent blocks in zones of low meanstress. Arc-transverse belts that host thin, young volcanosedimentary cover sequences (with or without mineralized rock fragments), volcano-sedimentary basins, porphyritic intrusions and hydrothermally altered magmatic centers indicate significant potential for the future discovery of large gold and copper deposits. References Barley, M. E., Rak, P., and Wyman, D., 2002, Tectonic controls on magmatic-hydrothermal gold mineralization in the magmatic arcs of SE Asia, in Blundell, D.J., Neubauer, F., and von Quadt, A., eds., The Timing and Location of Major Ore Deposits in an Evolving Orogen, Special Publication 204, Geological Society of London. London, United Kingdom, p. 39-47. Bautista, B. C., Bautista, M. L. P., Oike, K., Wu, F. T., and Punongbayan, R. S., 2001, A new insight on the geometry of subducting slabs in northern Luzon, Philippines: Tectonophysics, v. 339, p. 279-310. Carlile, J. C., and Mitchell, A. H. G., 1994, Magmatic arcs and associated gold and copper mineralization in Indonesia, in van Leeuwen T. M., Hedenquist, J. W., James, L. P., and Dow, J. A. S., eds., Mineral deposits of Indonesia; discoveries of the past 25 years., Journal of Geochemical Exploration v. 50; 1-3, p. 91-142. Cooke, D. R., McPhail, D. C., and Bloom, M. S., 1996, Epithermal gold mineralization, Acupan, Baguio District, Philippines; geology, mineralization, alteration, and the thermochemical environment of ore deposition: ECONOMIC GEOLOGY, v. 91, p. 243-272. Corbett, G.J., and Leach, T.M., 1998, Southwest Pacific Rim gold-copper systems: Structure, alteration and mineralization, Society of Economic Geologists Special Publication 6, 240 p. Davies, H. L., 1991, Regional geologic setting of some mineral deposits of the New Guinea region, in Rogerson, R., ed., Proceedings of the Papua New Guinea Geology, Exploration and Mining Conference: Rabaul, Australasian Institute of Mining and Metallurgy, Melbourne, p. 49-57. Garwin, S., Hall, R., and Watanabe, Y., 2005, Tectonic setting, geology and gold and copper mineralization in Cenozoic magmatic arcs of Southeast Asia and the west Pacific, in Hedenquist, J., Goldfarb, R. and Thompson, J. (eds.), Economic Geology 100th Anniversary Volume, Society of Economic Geologists, p. 891-930. Hall, R., 2002, Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations: Journal of Asian Earth Sciences, v. 20, p. 353-434. Hamilton, W., 1979, Tectonics of the Indonesian region: U.S. Geological Survey Professional Paper, v. 1078, p. 345 p. Hayes, D. E., and Lewis, S. D., 1984, A geophysical study of the Manila Trench, Luzon, Philippines; 1, Crustal structure, gravity, and regional tectonic evolution: Journal of Geophysical Research. B, v. 89, p. 9171-9195. Hedenquist, J. W., Arribas, A., Jr., and Reynolds, T. J., 1998, Evolution of an intrusion-centered hydrothermal system; Far Southeast-Lepanto porphyry and epithermal Cu-Au deposits, Philippines: ECONOMIC GEOLOGY, v. 93, p. 373-404. Hedenquist, J. W., Claveria, R. J. R., and Villafuerte, G. P., 2001, Types of sulfide-rich epithermal deposits and their affiliation to porphyry systems: Lepanto-Victoria-Far Southeast deposits, Philippines, as examples, ProExplo Congresso: Lima, Peru, 29 p. (on CD). East Asia: Geology, Exploration Technologies and Mines - Bali 2013 23 l Tectonic and Structural Controls to Porphyry and Epithermal Mineralization in the Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific Steve L. Garwin Hill, K. C., Kendrick, R. D., Crowhurst, P. V., and Gow, P. A., 2002, Copper-gold mineralisation in New Guinea; tectonics, lineaments, thermochronology and structure, in Korsch, R. J., ed., Geodynamics of Australia and its mineral systems; technologies, syntheses and regional studies, Blackwell Scientific Publications for the Geological Society of Australia. Melbourne, Australia, p. 737-752. Sasso, A.M., and Clark, A.H., 1998, The Farallon Negro Group, Northwest Argentina: magmatic, hydrothermal and tectonic implications for Cu-Au metallogeny in the Andean back-arc: Society of Economic Geologists Newsletter no. 34, p. 1, 8-18. Hutchison, C.S., 1989, Geological Evolution of Southeast Asia, Oxford Monographs on Geology and Geophysics, 13, Carendon Press, Oxford, United Kingdom, 368 p. Sillitoe, R. H., 1988, Geotectonic setting of western Pacific gold deposits, in Bartholomew, M. J., Hyndman, D. W., Mogk, D. W., and Mason, R., eds., Basement tectonics: Characterization and comparison of ancient and Mesozoic continental margins; proceedings of the Eighth international conference on Basement tectonics, Basement Tectonics Committee, p. 665-678. Kerrich, R., Goldfarb, R. J., Groves, D. I., and Garwin, S., 2000, The geodynamics of world-class gold deposits; characteristics, space-time distribution, and origins, in Hagemann S.G., and Brown, P.E., eds., Reviews in Economic Geology, v. 13, p. 501-551. Knittel, U., Trudu, A. G., Winter, W., Yang, T. F., and Gray, C. M., 1995, Volcanism above a subducted extinct spreading center; a reconnaissance study of the North Luzon Segment of the Taiwan-Luzon volcanic arc (Philippines), in Knittel, U., ed., Volcanism in South East Asia: Journal of Southeast Asian Earth Sciences, v. 11, no. 2, p. 95-109. McCaffrey, R., 1988, Active tectonics of the eastern Sunda and Banda arcs: Journal of Geophysical Research, B, Solid Earth and Planets, v. 93, p. 15,163-15,182. McCaffrey, R., 1996, Slip partitioning at convergent plate boundaries of SE Asia, in Hall, R., and Blundell D. J., eds., Tectonic evolution of Southeast Asia, Geological Society of London Special Publication 106, p. 3-18. Mitchell, A. H. G., and Leach, T. M., 1991, Epithermal gold in the Philippines; island arc metallogenesis, geothermal systems and geology, Academic Press, London, United Kingdom, 457 p. Pautot, G., and Rangin, C., 1989, Subduction of the South China Sea axial ridge below Luzon (Philippines): Earth and Planetary Science Letters, v. 92, p. 57-69. Richards, J.P., Boyce, A.J., and Pringle, M.S., 2001, Geological evolution of the Escondida area, northern Chile: a model for spatial and temporal localization of porphyry Cu mineralization, Economic Geology, v. 96, p. 271-305. Scholz, C. H., and Small, C., 1997, The effect of seamount subduction on seismic coupling: Geology, v. 25, p. 487-490. Sillitoe, R. H., 1989, Gold deposits in western Pacific island arcs; the magmatic connection, in Keays, R. R., Ramsay, W. R. H., and Groves, D. I., eds., The geology of gold deposits; the perspective in 1988, Economic Geology Monograph 6, p. 274-291. Sillitoe, R.H., and Hedenquist, J. W., 2003, Linkages between volcanotectonic settings, ore-fluid compositions, and epithermal precious-metal deposits, in Simmons, S. F., and Graham, I., eds., Giggenbach Volume, Special Publication 10, Society of Economic Geologists and Geochemical Society, p. 315-343. Skewes, M.A., and Stern, C.R., 1995, Genesis of the giant late Miocene to Pliocene copper deposits of central Chile in the context of Andean magmatic and tectonic evolution: International Geology Review, v. 37, p. 893-909. Yamada, N., Saito, E., and Murata, Y., 1990, Computer-generated geologic map of Japan, 1:2,000,000 Map Series, No. 22, Geological Survey of Japan, Tokyo, Japan. Yang, T. F., Lee, T., Chen, C. H., Cheng, S. N., Knittel, U., Punongbayan, R. S., and Rasdas, A. R., 1996, A double island arc between Taiwan and Luzon; consequence of ridge subduction: Tectonophysics, v. 258, p. 85-101. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 24 l 3D Modelling of Geology and Gravity Data: Summary Workflows for Minerals Exploration Helen Gibson, John Sumpton, Des FitzGerald, Ray Seikel 3D Modelling of Geology and Gravity Data: Summary Workflows for Minerals Exploration Helen Gibson1, John Sumpton1, Des FitzGerald1 and Ray Seikel1 Abstract Introduction 3D geology modelling coupled with innovative approaches to interpreting gravity data are combined in a suite of workflows available to assist minerals exploration. Challenges facing explorers - such as those relating to complex geology and structure, and how to achieve low-cost exploration - are being met with new software tools. Predicting the continuity of mineralised zones and faults away from mapped and sampled regions can now be rigorously constrained using GeoModeller which offers a highly appropriate 3D interpolation method. Intrusions, overturned limbs, faulting, and thin & irregular bodies (e.g., dykes and veins), can be modelled implicitly, constrained by measured contacts and orientations, including from drill holes. GeoModeller is geology modelling software developed and commercialised in Melbourne, Australia by Intrepid Geophysics in co-operation with the BRGM, France. The geophysical methods described in this paper are implemented in Intrepid software which was developed and commercialised in Melbourne, Australia – solely by Intrepid Geophysics. Why are we interested in potential field data as an aid to geological resources mapping and exploration? Insufficient geology observations often exist and so hamper reliable construction of the full geological and structural story, particularly at depth. Beyond surficial and drilled geology data, model constraints can also be derived from ground or airborne gravity data. Here we introduce one innovative interpretation workflow: Multi-Scale Edge Detection (Hornby et. al., 1999) which can facilitate semi-automated structural interpretation for the model zone, given certain caveats and uncertainties (see below). Searching for mineralisation can sometimes be successfully aided by simplifying the problem to: “Where do we have excess density clusters that are required by our measured gravity field, but cannot be explained by our best-known and modelled host geology?” In this workflow, we describe a non-deterministic geophysical inversion method which maintains a link to realistic 3D geology, and references observed gravity to drive results in terms of (i) geological uncertainty and (ii) a 3D grid of most-probable variable density. These inversion-outcomes may be used to again refine the geological model, and importantly to generate drilling targets centred on unexplained high-density clusters which may be a proxy for the location of unmapped sulphide-hosted mineralisation. The model-building interpolators The 3D interpolation method employed by GeoModeller is based on potential field theory (McInerney et al, 2005). Uniquely it enables cokriging of two related variables (geology & fault contact points and orientation data) by treating them as increments and derivatives of an isopotential surface of a 3D scalar field (Lajaunie et al., 1997; Fig. 1A). Cokriging therefore enables geology formationboundary positions to be computed in 3D as curvilinear surfaces which honour coupled dip & dip-direction data (orientation data are treated as gradients of the potential field). Multiple geology surfaces and fault planes can be interpolated separately – (e.g., of host sediments, intrusives, veins, dykes, and faults). When interpolating separately, the final model construction of aggregated volumes and fault surfaces honours a rule-based approach obeying the relationships of the pile (i.e., onlapping or erosional) and also obeying the chronology of the fault network. Both of these rule-based inputs are important constraints of the model, and are additional to the fundamental contact and orientation data. By this method, computation of the geological model using all constraining data is rapid, taking only seconds on a standard PC. Rendering the model in 2D & 3D views takes longer, depending on required resolution. GeoModeller models are easily updated and re-computed when new data becomes available with progressive drilling, sampling and/ or mapping. 1. Intrepid Geophysics, Unit 110, 3 Male Street, Brighton, Victoria 3186, Australia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 25 l 3D Modelling of Geology and Gravity Data: Summary Workflows for Minerals Exploration Helen Gibson, John Sumpton, Des FitzGerald, Ray Seikel Multi-Scale Edge Detection – aiding structural interpretation This semi-automated method implemented in GeoModeller applies either to gravity or magnetic data, and relies on producing unbiased estimates of sharp lateral changes in rock properties (FitzGerald & Milligan, 2013). The aim is to identify depth, location and shape of the sources reflected, say in the gravity data. The assumption is that the position of the maxima in the horizontal gradient represents the edges of the source bodies. Such maxima can be detected and mapped as points, and later converted to poly-lines or “worms” - potentially providing evidence, for example, for continuation of known structures or contrasting geological units in a model zone under construction. The process of mapping maxima as points can be extended to many different levels of upward continuation of the potential field data. This provides points and poly-lines that can be displayed in three dimensions, using the height of upward continuation as a pseudo z-dimension. In MultiScale Edge analysis a further assumption is that lower levels of upward continuation map nearsurface sources, while higher levels map deeper sources. Whilst generally true, this aspect must be treated with caution due to the non-uniqueness of potential field solutions. In recent years efforts to enhance the usefulness of this technique for fully automated interpretation have focused on solving the non-uniqueness issue for the estimation of “true” depth of sources. One candidate lies in the established Euler/Werner deconvolution technology (FitzGerald et al., 2004). This technology offers promise, but a robust technique is still under development. Nonetheless, the currently available tool can offer a good semi-automated workflow, offering some structural mapping constraints when depth-corrections are treated as qualitative (Fig1B). Figure 1. Non-deterministic inversion of gravity data Next, with our geology model closer to reality than before, mean densities can be assigned to each geology unit. But if some are unknown, a property optimization routine can first be run to determine optimum values. At this stage, several forward modelling runs are necessary to compute the gravity response directly from 3D geology and the coupled properties data. When a fairly close match is achieved between the modelled and observed gravity – then preparations for a litho-constrained stochastic inversion are complete. [Note that property optimisation, forward modelling and inversion are all performed on a discretised East Asia: Geology, Exploration Technologies and Mines - Bali 2013 26 l 3D Modelling of Geology and Gravity Data: Summary Workflows for Minerals Exploration version of the smooth 3D geology model (Fig. 1C). This necessary step creates a 3D grid or “voxet” model, for computation purposes.] During inversion, as employed in GeoModeller (McInerney et. al., 2005), each iteration makes a modification to one cell in the voxet, either in terms of geology-geometry, or the rock property (density). The revised geophysical response is recomputed following the small change, and assessed against observed gravity. If the misfit is better than for the last iteration, the model is kept. If the misfit is worse, the model is generally (but not always) rejected. This inversion method is based on a Markov Chain Monte Carlo formulation. Hence, rather than iterations ceasing when misfits reach a specified low limit (a deterministic approach), inversion employed in GeoModeller continues to iterate, exploring millions of possible models while converging to an overlap zone representing all models supported by the available independent data sets (Fig 1D). Retained models are within tolerance of the known geology & properties, and these are the basis from which inversion outcomes are reported in terms of probabilities. Specific outcomes from inversion of 3D geology and gravity: Excess density Performing an inversion on gravity data may have multiple goals, but here we highlight a workflow which may be useful in identifying zones of excess density. That is, zones where the best-known geology model still cannot explain the observed gravity response, and the driven inversion outcome in terms of most-probable density voxet, indicates clusters of high-density cells which are interpreted to indicate significant sulphide mineralisation (Fig 1E). In our experience this workflow is best applied in highresolution to prospect-scale models, and uses ground Helen Gibson, John Sumpton, Des FitzGerald, Ray Seikel gravity data. Sometimes our recommended workflow involves sensitivity testing, using multiple inversion runs commencing from different initial models, for example, with and without mapped gossans and their predicted depthextensions into mineralized zones. A project is deemed to bear results worthy of further exploration, when inversion outcomes yield cells of anomalously high density, within a variable density voxet. A filtered view of the voxet, say at > 3.3 gcm-3, enables geo-location of high density clusters, and thus targets. Post-inversion volumetrics and density statistics are also available for what was usually a poorly constrained zone of the initial model. Summary note Numerous workflows using the software tools available in GeoModeller and Intrepid aim to offer powerful solutions to exploration problems (Fig 1). References Hornby, P., Boschetti F., and Horowitz F.G., 1999. Analysis of potential field data in the wavelet domain: Geophysical Journal International, 137, 175-196. FitzGerald, D. and Milligan P., 2013. Defining a deep fault network for Australia, using 3D “worming”. ASEG 2013, in prep. FitzGerald, D., Reid, A., and McInerney, P., 2004, New discrimination techniques for Euler deconvolution: Computers&Geosciences, 30, 461–469. Lajaunie, Ch., Courrioux, G., and Manuel, L., 1997, Foliation fields and 3D cartography in geology: principles of a method based on potential interpolation: Mathematical Geology, 29, 571–584. McInerney, P., Guillen, A., Courrioux, G., Calcagno, P. and Lees, T., 2005. Building 3D geological models directly from the data? A new approach applied to Broken Hill, Australia. Digital Mapping Techniques pp 119130. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 27 l Chinese Minerals Exploration Methods and Philosophy: Implications for Out-bound Investment Matthew R. Greentree, Gavin Chan Chinese Minerals Exploration Methods and Philosophy: Implications for Out-bound Investment Matthew R. Greentree1* and Gavin Chan2 Explorers in China rely on a set of prescriptive National Standards to provide guidance on all aspects of mineral exploration, which cover Resource and Reserve Classification, principals of mineral exploration, technical requirements for field work, reporting and contain guidelines for individual minerals or mineral types (e.g. Liu and Zhou, 2003; Bucci et al, 2006). These guidelines leave little flexibility for exploration personnel to design exploration programmes that fit with local conditions, local experience, geology and mineralisation styles. The aim of this paper is to discuss how the Chinese National Standards (National Standards) originated and how they influence the way Chinese companies and State Owned Enterprises (SOE) approach minerals projects within China and overseas. During the mid to late twentieth century, the Chinese mineral industry was tightly controlled by government policy, operating independently of commodity markets and instead relying on complex system of quotas used to control mineral production. Mineral exploration was conducted by government agencies such as the Geological Brigades and Gold Squads who were organised at both county and provincial levels with oversight from National institutes such as the China Geological Survey. The role of these groups was to conducted similar work programmes to that of geological surveys in the west. However, the role of the geological brigade also included mineral exploration, development of mineral Resources and mining. These systems were still largely in place, until reforms began in the late 1980’s and many of the state owned and operated organisations were incorporated and became more autonomous. China started developing a series of National Standards for mineral exploration during the 1950’s based on the standards used within the Soviet Union. By 1959, the Chinese standards were issued by the State Commission of Mineral Reserves (SCMR) and again in 1983. The SCMR issued standards concerning mineral Resource and Reserve classification, principals of mineral exploration and exploration codes of individual minerals types. More recently, the standards have been issued by General Chinese National Standards Exploration stage Work programme Result Regional geological assessment Regional Mapping Typically regional reconnaissance style geological mapping at 1:1 000,000 to 1:25,000 scale. May include soils, stream sediment sampling and rock chip sampling. A number of defined targets or prospects Reconnaissance Target generation based geochemistry, mapping and limited drilling. Additional reconnaissance drilling, sampling and mapping. Work conduced at 1:50,000 – 1:10,000 scale. Prospecting Sampling at scales 1:10,000 to 1:5 000. Soils sampling, trenching and geophysics. Limited drilling and some Potential mineralisation assessed by “Preliminary Study” which covers economic, social or technical factors that may affect any decision to proceed Broad spaced drilling of identified mineralisation General Exploration (resource at inferred level Chinese standards). Detailed Exploration Systematic drill-out (resource at indicated level Chinese Standards) Pre-feasibility study including metallurgical testing carried out by mine design institutes. Feasibility study and resource to be used for mine design carried out by mine design institutes and application for mine license Table 1 Exploration stages as defined in the Chinese National Standards 1. SRK Consulting Australasia, 10 Richardson Street, West Perth, WA Australia 6160 Corresponding author: [email protected] 2. SRK Consulting Hong Kong, Suite A1, 11/F, One Capital Place, 18 Luard Road, Hong Kong East Asia: Geology, Exploration Technologies and Mines - Bali 2013 28 l Chinese Minerals Exploration Methods and Philosophy: Implications for Out-bound Investment Administration of Quality Supervision, Inspection and Quarantine and the China Geological Survey. The National Standards describe in detail how each phase of work is conducted. The Standards state specifications for different commodity types and include specifications for exploration methods, sample spacing, depth of drilling, assay schemes and cut-off grades. Exploration work outlined by the National Standards focuses on surface geochemical sampling methods including streams sediment, soils, rock chip, trenching and pitting. Although accesses to airborne geophysical methods are becoming more common, they are not routinely used in mineral exploration in China as they are by western geologists. The National Standards divided exploration cycle into stages which are; reconnaissance, prospecting, General Exploration and Detailed Exploration (Table 1). Each stage is matched to a level of detail and type of work conducted. Detail of work is linked to map scale (1:200,000; 1:50 000, 1:10 000 and 1:1 000) and sampling density. At the conclusion of General Exploration and Detailed Exploration stages there includes recommendations for mining studies. As most details of exploration are prescribed in the National Standards, this provides little encouragement for the geologist to assess the local geology and assay results systematically. This differs philosophically and practically from western exploration methods (e.g. JORC). Western exploration focuses on the judgement of a competent person, familiar with the commodity or deposit style, to design a site-specific/appropriate exploration programme, and supervise any exploration or Resource development work. The National Standards have been used successfully in many exploration programmes across China. However, the prescriptive approach outlined in the National Standards has a number of shortcomings particularly if an exploration programme is designed to follow the National Standards at the expense of decisions based on technical merit. Exclusively following these standards is likely to lead to an inefficient exploration programme in terms of time or cost and could result in an ineffective exploration programme. With changes to government policy in 2006 to encourage direct investment by Chinese companies overseas, China Matthew R. Greentree, Gavin Chan has become the largest source of investment for Resource projects worldwide. During 2011 Chinese investment within the Australian Resource sector reached USD 7.4 billion (Ferguson and Hendrischke, 2012). Increasingly, Chinese companies tend not to just acquire or invest in projects with established Resources, but begin actively exploring and developing greenfield Resource projects overseas. Many of the professionals within these organisations will continue to apply the National Standards on which they base exploration work and investment decisions. The additional cost required to bring exploration programmes designed according the National Standards to a western standard is difficult for many Chinese exploration companies to justify. However, exploration results and Resource estimates based on the National Standards are generally not accepted for the public reporting on either Asian (e.g. HKEx or SGX) or western stock exchanges (e.g. ASX, TSX, AIM). This is a significant challenge for Chinese organisations if they move to IPO or attempt to gain obtain funding from outside of China. This can be overcome with a “hybrid” of Chinese and western exploration methods. With the National Standards being followed, thus fulfilling any obligations to the Chinese parent company and incorporating aspects of western exploration (sampling, QA/QC, drill spacing, continuity of mineralisation etc.) that satisfy a Competent person under JORC. References Bucci L., Hodkiewicz, Jankowski P., Guibal D., Song X., 2006 JORC and the Chinese Resource Classification Scheme – an SRK view. AusIMM Bulletin Feature Exploration July / August pp 24 -27 Ferguson D. and Hendrischke H., 2012 Demystifying Chinese Investment – Chinese Direct Investment in Australia. KPMG & University of Sydney China Studies Report pp 20 JORC, 2012. Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code) Available from: http://www.jorc.org> (The Joint Ore Reserves Committee of The Australasian Institute of Mining and Metallurgy, Australian Institute of Geoscientists and Minerals Council of Australia). Liu R. and Zhou eds. 2003 Compilation of commonly used standards for geological exploration. Sichuan Metallurgical and Geological Bureau East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l keynote 29 Realising the Mineral Potential of Mongolia Graeme Hancock Realising the Mineral Potential of Mongolia Graeme Hancock1 The land mass of Mongolia is formed from a series of accreted terranes sandwiched between the North Asian Craton to the north and the Sino-Korean Craton to the south. The main accretion events appear to have taken place during the early to late Paleozoic and the terranes comprise both island arc sequences as well as blocks of preCambrian basement and granites. These accreted terranes have subsequently been subjected to a series of intrusive and volcanic episodes. The accreted formations are overlain by sedimentary rocks dating from periods of tropical climate sedimentation creating large basins of coal bearing sediments. This combination of events has resulted in a complex and highly prospective geological environment. Most of the mapping and interpretation of the geology was done by joint Russian and Mongolian geological teams during the period when Mongolia was a satellite State of the Soviet Union. During this time they identified over 8000 mineral occurrences covering 80 different mineral commodities as well as a significant number of mineral and coal deposits. The island arc terranes are highly prospective for copper, gold, uranium and a range of other metals and rare earth elements. The Permian aged island arcs also contain significant bituminous coal deposits. To date two copper deposits have been developed into producing mines (Erdenet during the socialist era and Oyu Tolgoi now commissioning) as well as two uranium mines (Dornod and Gurvanbulag) both of which were developed by Russia during the socialist era. Early gold exploration focused mainly on easily exploitable alluvial deposits, with more recent exploration more focused on hard rock occurrences. This modern gold exploration has resulted in the development of one significant gold deposit (Boroo Gold) and the discovery of a number of other significant prospects. Coal exploration and development has also received a lot of attention, particularly in the recent past with Permian bituminous coals now being exploited from a number of deposits and exported into the Chinese coking coal market. Huge deposits of younger lignite and sub-bituminous coals occur extensively throughout the central, north and eastern parts of the country providing fuel for the country’s thermal power and heating plants. In common with many developing countries Mongolia faces a number of challenges in realising the development of this significant mineral potential. A combination of poorly developed infrastructure, a sometimes unstable legal and regulatory environment coupled with some unfriendly foreign investment rules have discouraged many explorers. When combined with the issues the Mongolian Government faces as a landlocked country in managing the geopolitical influences of its two immediate and powerful neighbours (Russia and China) it all creates a unique set of interesting challenges and opportunities for mineral exploration and development. 1. President and Chief Representative, Mongolia, AngloAmerican Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l keynote 30 A Framework for China’s Gold Exploration and Endowment Craig J. R. Hart, Richard J. Goldfarb A Framework for China’s Gold Exploration and Endowment Craig J. R. Hart1 and Richard J. Goldfarb2 Among the most dramatic change in the global gold exploration and mining landscape during the past ten years is the significant development of China’s gold industry to that of the global leader in gold production. First in gold production since 2008, China now produces more than 400 t of gold/year representing 10% of global production and surpassing Australia (250t) and USA (230t). Importantly, production has been increasing at almost 12% yearover-year which contrasts most other traditional gold producing countries that now lack growth. Such production advances have been made with increased investments and efficiencies in existing mines, consolidation of small mines, the application of technologies to increase recoveries of gold from low-grade and refractory ores, and greenfields and brownfields exploration and discoveries that result in the development of new mines. However, China’s gold mines, of which there may be more than 1000, are typically small in terms of both production and resources with few approaching world-class status. China’s ‘official’ gold resource has grown to 1900t, but is likely inflated, and represents only 3.7% of the global resource and would be exhausted with only five years of production. The influx of foreign explorers and miners and expertise to China peaking in 2004 significantly catalysed the industry such that the benefits are still prominent despite changing policies starting in 2008 that discouraged foreign investment. The industry has changed 180 degrees such that Chinese cash is playing an increasing role to off-shore corporate ownership and mineral exploration and mining development efforts. China’s gold mines have traditionally been prominent in the eastern part of the country where high population density has ensured that most small deposits were discovered and exploited by underground methods, and these mines were important contributors to China’s historical production. With increased political emphasis on development of the county’s western frontiers, new discoveries have been made in regions such as Xinjiang, Qinghai, Gansu and Tibet. However, the country’s largest mines are those historical underground producers that have been consolidated and expanded with infrastructure capital that was difficult to obtain prior to 2009. Examples of consolidated and expanded mines are those in the Shandong province that now have the capacity to produce >26t Au/year, and Zijinshan high sulphidation epithermal deposit now generating 15.5t/year. A key step forwards was the development of large open pit gold mines by foreign companies. First in this effort was the discovery and development of the CSH deposit by Canadian junior explorer Jinshan Gold Mines, which was developed prior to their takeover by China National Gold Corp and will expand to more than 8t of annual production by 2015. Prominent also, are the efforts of Eldorado Gold Corp who, including their takeover of SinoGold in 2009 for $2.2B, have put three gold mines into production ( Jinfeng, Tanjianshan, White Mountain) that are generating ~11t of annual production. Not all involvement of foreign companies has been positive, with Southwestern Gold’s manipulation of resource data at the Boka gold deposit and failure of the government to provide development permits to Mundoro Resources for development of their 30t Maoling deposit, as examples. China is composed of several Archean cratonic blocks that were amalgamated in the late Paleozoic to early Mesozoic to form the Precambrian regions of present-day China. The assembly of these blocks was associated with numerous episodes of Phanerozoic tectonic activity that caused their margins to become deformed and modified. These Phanerozoic orogenic belts overprint and reworked the margins of cratonic blocks and overlying sedimentary rocks and generated magmas that formed plutonic and volcanic assemblages. Most of China’s orogenic, epithermal, skarn, porphyry, and Carlin-like gold deposits and resources are in or proximal to these modified cratonic margins. Accordingly, China’s major gold provinces are preferentially located along the northern, eastern and southeastern margins of the North China craton, along the various margins of the Yangtze craton, in the Tianshan and Altaishan orogenic belts adjacent the Tarim and Junggar blocks in northwestern China. Eastern China was subsequently influenced by Pacific subduction that generated magmas, porphyry and epithermal systems in southeastern China, and the collision with India generated Himalayan orogeny that generated small orogenic and porphyry systems. 1. MDRU-Mineral Deposit Research Unit, The University of British Columbia, Vancouver, BC, Canada Corresponding author: [email protected] 2. United States Geological Survey, Box 25046, MS 973, Denver Federal Center, Denver, CO, USA East Asia: Geology, Exploration Technologies and Mines - Bali 2013 31 l A Framework for China’s Gold Exploration and Endowment Three-quarters of China’s gold-only (mostly orogenic) deposits occur within uplifted blocks of Precambrian metamorphic basement rocks along the margins of the North China craton and include those in the Shandong, West Qingling, Xiaoqingling, Daqinshan, Yan-Lioa and Changbaishan gold provinces (). However, unlike many other regions of the world where important enrichments of gold mineralization are directly related to Archean or Paleoproterozoic basement terranes, no important Precambrian gold systems have been recognized anywhere in China. All of China’s gold endowment formed in response to Phanerozoic events. This is a globally unique situation in which significant accumulations of Phanerozoic gold were deposited in Precambrian rocks. The old rocks are typically not receptive to younger tectonic, magmatic or thermal events due to the rigid integrity provided by their thick, cold and stiff lithosphere. The widespread distribution of orogenic gold deposits throughout eastern China appears to be broadly related to subduction beneath them, which warmed and softened their margins and allowed heat, magmas and fluids to infiltrate their margins as early as initial Permo-Triassic amalgamation. Lithospheric softening of the margins to the North China block, either by delamination or thermal erosion, was particularly dramatic Craig J. R. Hart, Richard J. Goldfarb during the Jura-Cretaceous and resulted in the loss of subcontinental lithospheric mantle (the Archean-Proterozoic keel) which further destabilized and weakened the craton margins, leading to Yanshanian orogeny. This process was initiated by the subduction of three plates beneath eastern China, with subsequent fluid flow reflecting the changing stress regimes at ca 125 Ma that is coeval with China’s largest gold event. This setting is a dramatic departure from those typically accepted within orogenic gold models. China continues to overemphasize their already low resource levels. Most past gold discoveries were acquired through prospecting and systematic empirically-driven exploration. Future discoveries of large gold resources require the application of conceptual targeting and mineral deposit models, as well as improved understandings of the significance of regional geological setting and district-scale ore controls, these exploration approaches have not been previously widely applied. Future resource success will require amalgamating small underground deposits into larger open pits with lower grades. The influx of foreign explorers contributed new methods and strategies and ideas to China’s gold exploration and mining landscape and ultimately contributed to the production boom that China is currently enjoying. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 32 l The Tombulilato Copper Gold Project in Sulawesi, Indonesia ‘Facing the Challenges and Opportunities’ Dedy Hendrawan, Gayuh ND Putranto The Tombulilato Copper Gold Project in Sulawesi, Indonesia ‘Facing the Challenges and Opportunities’ Dedy Hendrawan1 and Gayuh ND Putranto1 Located in Gorontalo Province, Indonesia, Tombulilato Cu-Au District is a well known district which has potential Cu-Au mineralization to develop. The district is also located in Au-Cu mineralization trend (Figure 1). International Minerals Corp (IMC), a subsidiary of PT Bumi Resources Tbk that took over share ownership from BHP in 2005, began an exploration and drilling program in the south part of the District area in 2006. PT. Gorontalo Minerals (GM) owned 80% by the IMC and 20% by PT. Aneka Tambang (ANTAM) had continued exploration program since 2011 and commenced an extensive drilling program in Sungai Mak and Cabang Kiri in September 2011. The geology of the Tombulilato district, North Sulawesi (Perello, 1993), is characterized by an island arc-type volcano-sedimentary pile, > 3400 m thick and of late Miocene (?)–Pleistocene age, which is made up of submarine to subaerial basic to acid volcanic rocks interbedded with, marine and continental sedimentary rocks. The sequence is intruded by high-level stocks and dikes, and cut by diatreme breccias of late Pliocene and Pleistocene age, some of which are associated intimately with porphyry Cu–Au and epithermal Cu–Au–Ag mineralization. A main compressive deformation event took place in the Pliocene. Preliminary geologic reconstructions suggest that these mineralization types in the Tombulilato area were generated over about 2 M yr (between 2.9 and 0.9 Ma) as part of a district-scale hydrothermal system. Continuous syn-mineralization uplift and erosion, which are interpreted to have removed some 2 km of rock in the last 3 M yrs, were responsible for the progressive un-roofing of the hydrothermal system and the superposition of epithermal environments over relics of higher temperature, deeper-seated mineralization. In the near-surface environment, intense uplift accompanied formation of a chalcocite blanket at Sungai Mak. The structure of the Tombulilato District is characterized by northerly striking high-angle faults, normally a few meters wide and containing tectonic breccias, high-tomoderate angle normal faults showing an easterly trend and of post-mineralization origin, and common low-angle thrust faults, typically accommodated by ductile sedimentary intercalations in the Bilungala Volcanics and showing a random orientation. All intrusive bodies postdate folding and thrusting (Leeuwen and Pieters, 2011). Figure 1. Tombulilato District and prospect locations 1. PT Gorontalo Minerals, Gedung Leppin Jln Sawah Besar 300, Bone Bolango, Gorontalo, Indonesia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 33 l The Tombulilato Copper Gold Project in Sulawesi, Indonesia ‘Facing the Challenges and Opportunities’ Dedy Hendrawan, Gayuh ND Putranto Three main mineralization types are present in the district: 1. porphyry Cu–Au; 2. high-sulfidation epithermal Au-Cu-Ag; and 3. low-sulfidation epithermal Au–Ag. Porphyry Cu– Au mineralization is present at Cabang Kiri (East, North, Southwest and South), Sungai Mak, Kayubulan Ridge, and Cabang Kanan. High Sulphidation epithermal Au-Cu-Ag is present in Motomboto (North, East and West), Mohutango and Ridho. Low Sulphidation Au-Ag is present in Kaidundu, Mamungaa, Pombolo, Hulapa, Ombulo, Hupito, Moota, Waluhu, and Bilolatunga (Figure 1). Hypogene Cu-Au is 72.2mt @ 0.31% Cu and 0.17gr/t Au and 3. Sungai Mak Oxide Au is 11.5mt @ 0.51gr/t Au. Most of resource was fall in measured-classification. Mineral resource of Cabang Kiri is 124mt @ 0.43% Cu and 0.67gr/t Au. In order to support and accelerate the completion of FS and AMDAL, before 2011 and during the resource drilling period in 2011-2012, GM had also completed numbers of test and studies including metallurgy, geotechnical, geohydrology, hydrology, baseline study, health study, social impact study, flora/fauna study, marine biota study, etc. SRK Consulting as a main consultant, LAPI ITB, Simulus and Io Global are some of reputable consultants that have been involved with GM from the beginning of recommencement of exploration in 2011. Reputable national universities (ITB, UNHAS, UNSRAT, UNTAD, UNG, UG, IPB and UI) and international institution (ANU) had been involved conducting numbers of baseline studies to support the Feasibility study (FS) and Environmental Impact Study (AMDAL). Other consultants are Paradigm Management Consulting (PMC) and Ernst and Young who assisted GM in developing Integrated Management System and QHSE Management System. Current JORC resource from Sungai Mak and Cabang Kiri reported in 2012, new resource from Motomboto area expected to get in 2013, potential additional expansion from these three prospects and other resources from known prospects including Kayu Bulan, Cabang Kiri North, Cabang Kanan, and numbers of clusters in Motomboto and Kaidundu-Pombolo are very possible that Tombulilato District will prove to be a world class Copper-Gold District. Regional exploration program during 2011-2012 assisted by effective target selection from data collection, data compilation and data processing of geophysics data (airborne and IP) and geochemistry data had also successfully located new large Cu-Au anomalies (Poga, Ridho, Kayu Bulan Barat, and other cluster at South). In the Bumi Resources era in between 2006 and 2010, GM conducted minor scale but systematical exploration program in the south part of Block 1, especially in Kaidundu prospect and its surroundings. Started in mid 2011, GM started running extensive drilling program targeting to bring the project into production in 2016-2017. This is a challenging task. Challenges includes legal and permitting, compiling old analog data, building new team, building new system and infrastructures, building good relationship with stake holders, facing public perception, working in remote and rugged terrain, working together with local miners, financing the project, maximizing local contractors, implementing and monitoring HSE aspects, etc. Exploration strategy and timing is also critical in developing this project to achieve and fulfill the target and expectation of the government in line with the exploration stage in the Contract of Work stage period after long inactive period of exploration. In the other hand, developing, implementing and maintaining Health, Safety and Environment (HSE) are very important to conduct in all aspect of activities. Expansive drilling program over Sungai Mak and Cabang Kiri was conducted during 2011-2012, totaling 15197.95m in Sungai Mak and 5983.05m Cabang Kiri. The drilling program included twin holes, resource holes metallurgy holes, and geotechnical holes. Current JORC minerals resource of Sungai Mak and Cabang Kiri using 0.2% Cu cut-off grade was reported by competent person of SRK in July 2012. Sungai Mak resource are divided into 3 mineralization domains: 1. Sungai Mak Supergene Cu-Au is 84.3mt @ 0.84% Cu and 0.42gr/t Au, 2. Sungai Mak Significant reduction in numbers of people working in local artisanal gold mining Au activity in Motomboto from 5000-7000 people in 2011 to approximately 700 people in End of 2012 has opened access and opportunity to conduct exploration program in the area. BHP reported in 1997 that Tulabolo prospect or what we currently call Motomboto North has high grade Au-Ag-Cu at 3.5mt @ 4.8gr/t Au, 94.3 ppm Ag, 1.67% Cu (BHP and ANTAM, 1992). Because of these reasons, GM plans to conduct exploration and resource drilling program over Motomboto North and Motomboto East in 2013. Motomboto complex has numbers of clusters located along WNW structures associated with a multiphase of hydrothermal breccias complex. Main mineralization occurs in sulphides-cemented breccia and vuggy silica, both as oxide and sulphide Au-Cu-Ag. Oxide Au near the surface at Motomboto North is the first priority to complete followed by higher tonnage and higher grade of Au-Ag in Main Motomboto East. New resources from both prospects are expected to get in end of year 2013. PT. Gorontalo Minerals has successfully overcome the challenge to get high level confidence of mineral resource and increase more tonnage and grade in the past 1-2 year exploration program. The company is now moving to complete detail Feasibility Study of Motomboto North, Motomboto East and Sungai Mak in 2013 followed by Environmental Impact Study (AMDAL) in 2014 and construction stage in 2015-2016. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 34 l Geophysics of the Elang Cu-Au Porphyry Deposit, Indonesia, and Comparison with Other Cu-Au Porphyry Systems T. Hoschke, S. Schmeider, S. Kepli Geophysics of the Elang Cu-Au Porphyry Deposit, Indonesia, and Comparison with Other Cu-Au Porphyry Systems T. Hoschke1, S. Schmeider2 and S. Kepli2 Introduction The Elang porphyry Cu-Au deposit is located in south western Sumbawa in Indonesia approximately 60 km due east of the Batu Hijau porphyry Cu-Au mine (Figure 1). It is a large deposit with a total resource estimate (as at June 2010) of 2425 Mt at 0.33 g/t Au and 0.31 g/t Cu (Ball, 2011). A regional stream sediment sampling and mapping program in 1987 and 1988 led to the discovery of epithermal veins in the Elang area. Gold mineralisation was intersected in drill holes, but not enough to be of interest and exploration ceased until after the discovery of Batu Hijau in 1991. The area was then reassessed for porphyry Cu potential and a large low grade resource was discovered, however this was not considered economic at the time. Another phase of exploration began in 2002 and significantly added to the resource to the south under a lithocap up to 200 m thick. The deposit is associated with a series of tonalite porphyry intrusions that are hosted by andesitic volcanics (Maula & Levet, 1996). The geology and alteration are shown in Figures 2a and 2b, respectively. Mineralisation is associated with potassic alteration (chlorite-magnetite±biotite) which grades outward to propylitic alteration. This system is overprinted by intermediate argillic alteration and an advanced argillic lithocap, up to 200 m thick, covers much of the deposit. The Elang area was covered by an airborne magnetic survey in 1993 and with ground magnetics and Gradient array IP/resistivity surveys at about the same time. Pole-dipole IP/resistivity surveys were conducted from 2003 to 2005, HoisTEM and NewTEM were flown in 2004 and an airborne magnetic and radiometric survey in 2012. Magnetic Response A helicopter magnetic and radiometric survey flown by Newmont in 1993 covered a large part of SW Sumbawa, including the Batu Hijau and Elang areas. The survey was flown in an east west direction with 200 m spacing between flight lines. A more recent survey was completed in 2012 with 100m spaced north south lines. Figure 1. Location of Elang on SW Sumbawa In the 1993 survey Elang shows up as a discrete magnetic high of about 700 nT within a magnetically quiet area. The better resolution of the ground magnetic survey and the 2012 airborne survey shows two discrete highs (Figure 2c). The magnetic highs are due to magnetite associated with the potassic alteration zone of the mineralised tonalite porphyries. This contrasts with a broader zone of magnetite destructive clay alteration. The low between the two magnetic bodies is probably due to a less magnetic late tonalite intrusion (the Echo Tonalite).The larger southern body lies under the lithocap at a depth of up to 200m depending on topography. The magnetic data were inverted in 3D and the potassic zone, as determined by drilling, correspond well to the zones of high magnetic susceptibility in the inversion model. Magnetic susceptibility measurements on drill core confirm that the mineralised potassic zone is moderately to highly magnetic. Electrical Response IP surveys Gradient array IP/resistivity surveys were conducted over Elang with a line spacing of 200 m and an electrode spacing of 50 m. There are strong chargeabilities associated with the 1. Consulting Geophysicist, Perth, WA Corresponding author: [email protected] 2. PT Newmont Nusa Tenggara East Asia: Geology, Exploration Technologies and Mines - Bali 2013 35 l Geophysics of the Elang Cu-Au Porphyry Deposit, Indonesia, and Comparison with Other Cu-Au Porphyry Systems Elang alteration system and a corresponding resistivity low. The lithocap was not detected in this survey. Pole-dipole IP surveys conducted between 2003 and 2005 covered the deposit and surrounding alteration system. The line spacing was 100 m or 200 m with a potential electrode spacing of 50 m reading to N=10. A 3D inversion was applied to the lines covering Elang. Very strong chargeabilities are associated with the porphyry alteration (Figure 2d). The limit of disseminated pyrite (sulphide shells of Lowell and Guilbert, 1970) is well defined, and drilling confirms a strong chargeability high on the eastern side of the survey is due to the pyrite shell of the porphyry system. A chargeability low immediately to the east of the deposit relates to a late dacite intrusion. Some of the more subtle lows may be due to late intrusive phases that are less mineralised. T. Hoschke, S. Schmeider, S. Kepli chargeabilities both in the ore zone and the pyrite halo. There is a broad resistive low due to clay alteration and sulphide veining which is not uncommon in porphyry systems. References Ball, R., 2011. Newmont Mining Corporation Presentation, CIBC Annual Instutional Investor Conference, Whistler, B.C. Lowell, J. D. and Guilbert, J.M., 1970. Lateral and vertical alterationmineralization zoning in porphyry ore deposits, Economic Geology 65: 373-408. Maula, S. and Levet, B.K., 1996. Porphyry Copper-Gold Signatures and the Discovery of the Batu Hijau Deposit, Sumbawa, Indonesia, in Australian Mineral Foundation, eds., Conference on Porphyry Related Copper and Gold Deposits of the Asia Pacific Region: Cairns, Australasian, August 12-13, 1996, Proceeding, p.8.1-8.13. The resistivity data clearly show the extent of the alteration system (~3km x 2km) with the porphyry alteration being relatively conductive at 10s of ohm-meters in a background of fresh volcanics in the 100s of ohm-meters. The highly resistive lithocap of 1000s of ohm-meters is well defined and the conductive zones are due to clay alteration and/or sulphide veining. Chalcopyrite veining in the potassic zone appears to be extensive and is probably a good conductor. This zone is generally too deep to be seen with the pole-dipole resistivity. Airborne Electromagnetics HoisTEM and NewTEM surveys were flown over Elang in 2004 and show similar results. The Elang alteration system clearly shows up as a NE trending conductive zone in relatively resistive volcanics. The leached cap is highly resistive and is clearly identified by the HoisTEM. There are other conductors in the area that may represent alteration zones and there is a conductive sedimentary unit on the western side of the area. Conclusion Elang is typical of a number of Cu-Au porphyry systems in that magnetite is associated with mineralisation and produces a strong discrete magnetic anomaly. It has a larger potassic zone than most systems, which may be due to more than one porphyry centre. The Elang system is more pyrite rich than many porphyries, leading to very strong Figure 2. Plans showing the geological and geophysical character of the Elang deposit. (a) Elang geology from mapping and projected from drilling. (b) Alteration.(c) Airborne magnetics – RTP (2012 survey). (d) Chargeability surface 200m below topography (from 2002-2004 surveys). The 0.3% Cu shell as defined by drilling is outlined in blue. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 36 l Controls on high-grade Au ore-shoots: Towards a New Paradigm J. M. A. Hronsky Controls on High-grade Au Ore-shoots: Towards a New Paradigm J. M. A. Hronsky1 Recent industry challenges associated with the development of large, low-grade deposits have once again highlighted the critical role of grade in profitable gold mining. For this reason and also because much gold exploration is increasingly focused at depth in known camps, it seems clear that a robust process understanding of controls on the irregular distribution of high-grade ore-shoots within a deposit should be an industry priority. Interestingly, the current structural targeting paradigm relating to this topic is seldom explicitly articulated, let alone challenged. Despite this, it has a strong influence on current approaches to near-mine targeting. This paradigm recognises (correctly) that well-mineralised rock volumes represent sites of anomalous ore-fluid flux. However it implicitly assumes these anomalous volumes represent localised more dilatant/ permeable rock volumes embedded within a surrounding, larger-scale, less focused fluid flow system and that they are generated by dynamic syn-ore deformation (eg Ridley, 1993). Based on the above assumptions, it is assumed that knowledge of deposit structural geometry and inferred syn-ore stress field can be used to predict the kinematics of these structures and hence anomalous dilational sites. This framework also implies that localised mineralised volumes hosted by structures such as faults and shear zones are intrinsically a property of these structures. The primary problem with this existing paradigm is that although individual examples of a close association between mineralisation and inferred dilatant geometries can be demonstrated, this is not a consistent predictive relationship and the concept fails in many deposits (eg Lancefield gold deposit, Hronsky, 1993; Cracow gold Deposit, Mickelthwaite, 2009). It is proposed here that the solution to this problem is provided by fundamentally changing our perspective on the physical relationship between ore-shoots and the fluid flow systems that host them. Hronsky (2011) proposed that most ore deposits can be considered as forming in transient fluidexit conduits, associated with the episodic rupture of overpressured reservoirs at depth. Fluid Exit Conduits are rock volumes that have been conduits for large amounts of fluid flux, usually over multiple cyclic events. They represent zones of localized intense fracturing and extreme crustal permeability. They are sourced from an overpressured reservoir zone at depth and are formed when a fluid pressure pulse breaks its way to the surface, taking the easiest path. This path of least resistance may involve the reactivation of existing structures but in many cases results in the formation of pipe-like fracture zones in previously intact rock. Stress changes associated with these fluid pulses are large and overwhelm the effect of the ambient stress field. This is the primary reason for the predictive failure of the existing paradigm as ore-shoots are constrained to be restricted to these fluid-exit conduit volumes, which will have geometries not predictable by traditional structural analysis. An important implication of this new perspective is that fluid conduits may be much more vertically-extensive features than the pre-existing structures which host them. A single fluid conduit may move between host structures as it propagates upward, depending on which pathway provides the path of least resistance. This may result in them following quite torturous paths from source to sink, including right-angled bends in three dimensions. The key control on conduit localisation (and hence ultimately ore-shoot location) is the rheological structure of rock mass above the source reservoir – what is the easiest path upward for the fluid pulse? In this context, ore-hosting fault and shear zones are effectively just another rock type. Usefully, from a predictive perspective, it is clear that some geometric patterns of rock rheological distribution are consistently more favourable. One of the most notable of these is where a steeply-oriented pipe-like volume of more brittle rock occurs within a weaker wallrock sequence. In this situation, the brittle pipe behaves like a “lightning rod” and commonly is preferentially used by the propagating fluid pulse. Ore-fluid conduits can be divided into two types, with important implications for near mine targeting. Type 1 conduits occur as pipe-like stockwork bodies, and are typically associated with large, coherent bodies of mineralisation of relatively uniform but generally low, grade. Porphyry-related stockwork deposits are a good example of Type 1 conduits but they also occur in other ore styles. Type 1. Western Mining Services and Centre for Exploration Targeting Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 37 l Controls on high-grade Au ore-shoots: Towards a New Paradigm J. M. A. Hronsky 2 conduits form complex, linked, vein arrays, which host local, smaller, discontinuous lenses of mineralisation (“ore-shoots”). In this conduit type, individual ore-shoots can be much highergrade than background parts of the host vein system. Most Low-sulphidation Epithermal and Orogenic Gold deposits are hosted by Type 2 conduits. Type 1 conduits are associated with the failure of previously intact rock whereas Type 2 conduits are associated with shear Figure 1: An example of application of the hierarchical framework of ore-shoot controls proposed in this failure of pre-existing planes of model– Mararoa Reef at Norseman. (Diagram modified after Campbell, 1990) weakness. In the case of Type 2 conduits, ore-deposition is heterogeneous along the conduit this reason, exploration must focus on the conduit system, zone, related to locally enhanced dilation and associated rather than the immediate local host structure. For example, pressure drop. This occurs because of the affect of the shear in a system dominated by near-surface, flat-dipping orecomponent on local structural heterogeneities along the host hosting structures, there must somewhere be more steeply structure (ie local “dilational jogs”). Importantly, these local oriented feeder conduits that bring in fluid flow from depth dilational volumes are not sites of greater fluid flux than and these should be a near-mine exploration target. adjacent segments of their host conduit – instead they are simply volumes of greater mineral (commonly dominantly Type 2 (ie Shear zone-associated) conduits will host local quartz) precipitation. These local heterogeneities represent a zones of dilatancy and hence are more likely to host local lower-order scale of control on ore deposition that is absent higher-grade shoots. In contrast, Type 1 conduits (eg from Type 1 conduit systems stockwork zones) will not host local zones of anomalous From a process perspective, the critical difference between Type 1 and Type 2 conduit systems is whether fluid-driven failure is purely extensional (Type 1) or has a shearcomponent (Type 2). It is proposed (following Cox, 2010) that these different states of fluid-pulse propagation depend on the ratio of lv (pore-fluid pressure factor) to differential stress (s1-s3), and that this, in turn, relates to factors such as paleodepth, fluid pressure (bigger systems more likely to manifest as Type 1 conduits) and distance from parental intrusion. There are a number of important practical implications of this revised perspective on hydrothermal ore emplacement. Because all deposits need to form as part of a fluid conduit system that connects an underlying fluid reservoir with a near-surface sink zone, exploration needs to focus on tracing the fluid conduit system (through barren segments) downward beneath known ore-shoots and prioritising these volumes for further follow-up exploration. Developing techniques for recognising such barren linking segments is therefore an important objective. For example, relatively subtle alteration in the plane of the lode may be much more important than stronger alteration elsewhere. Because the expected vertical extent of the fluid conduit system is commonly much greater than individual host structures, we predict conduits will use multiple structures at different vertical levels as they propagate to the surface. For dilatancy (at a relevant scale) and therefore will always be more uniform in grade, forming pipe-like ore volumes. Importantly for exploration, a Type 2 conduit that hosts one localised high-grade ore-shoot volume is very likely to host others. However, these may be separated by barren segments of the host conduit zone. When targeting these deeper extensions in Type 2 conduit systems, it is important to separate out conduit-scale from localised ore-shoot-scale plunge controls; exploration should focus down the plunge trend of the conduit not the localised ore-shoot. The key geological element for targeting in the near-mine environment is localised rheological heterogeneity (in 3D) because this is what overwhelming controls fluid conduit emplacement. Therefore near-mine geology must always be characterised with reference to rheology (note that in this context, pre-existing shear zones are really just a special type of weak rock). It is important to establish the geological process which defines the base of an ore-shoot – this will determine follow up exploration strategies. For example, if the base of the oreshoot is related to the termination of a local dilational zone, the exploration implications are very different from the case where the termination is related to the fundamental base of the zone of ore deposition. Ore-shoots can be hosted by all pre-existing structures not just the latest “syn-ore” ones; therefore the age of the host East Asia: Geology, Exploration Technologies and Mines - Bali 2013 38 l Controls on high-grade Au ore-shoots: Towards a New Paradigm structure is not necessarily the age of mineralisation (as has commonly been assumed in the past). In summary, in the 21st Century, rather than the more traditional “structure-centric” conceptual approach, a “fluidcentric” alternative is advocated for near-mine targeting. This approach has very important practical implications and has the potential to contribute to the more efficient discovery of high-grade gold ore shoots. References: J. M. A. Hronsky Hronsky J.M.A., 1993. The role of physical and chemical processes in the formation of gold ore shoots at the Lancefield deposit, Western Australia. PhD Thesis (unpubl.), University of Western Australia. 205p. Hronsky J.M.A., 2011. Self-organized critical systems and ore formation: The key to spatial targeting? Society of Economic Geology Newsletter, Vol. 84, 14-16. Micklethwaite S., 2009. Mechanisms of faulting and permeability enhancement during epithermal mineralisation: Cracow goldfield, Australia. Journal of Structural Geology 31, 288-300 Ridley J., 1993. The relations between mean rock stress and fluid flow in the crust: With reference to vein- and lode-style gold deposits. Ore Geology Reviews 8, 23-37 Campbell J.D., 1990. Hidden gold – The Central Norseman story. AusIMM Monograph 16 Cox S.F., 2010. The application of failure mode diagrams for exploring the roles of fluid pressure and stress states in controlling styles of fracture-controlled permeability enhancement in faults and shear zones. Geofluids 10, 217-233 East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l keynote 39 Ramping-up Exploration Value from Aeromagnetic Surveys – More Geological Input Needed! David Isles Ramping-up Exploration Value from Aeromagnetic Surveys – More Geological Input Needed! David Isles Aeromagnetic data can add a vast amount of geological information to a project area. The process of integrating aeromagnetics with geology, satellite imagery and radiometrics to produce ‘working project maps’ is straightforward: it is really an extension of the geological mapping process and the tasks involved closely parallel those used in conventional geological mapping. However, we frequently encounter high quality aeromagnetic data sets that are very poorly integrated with geology and other project data. This is partly due to inexperience in working with the aeromagnetics, partly due to inadequate allocation of (geologist’s) time to the integration task and partly due to a pre-occupation with quantitative geophysical interpretation tools. High quality acquisition and detailed survey specifications are the norm in the airborne magnetic industry, and a range of very good options is readily available for filtering and image enhancement. Most surveys flown yield excellent and appropriate imagery for interpretation, and the re-use of ‘old’ (post 1970s) survey data is also made easy by robust software for stitching and merging new and old surveys. Our ability to gather, process and present data is very well developed, but our tendency is to lose momentum after the ‘pretty pictures’ have been produced. While there are strategies for optimising the data processing and presentation stage to give interpreters the most appropriate imagery in the shortest possible time-frame, these do not cause substantial improvements to the final, integrated interpretation. The key ingredients that lead to high quality, high value interpretation are geological thinking and time. Aeromagnetic images depict the (3-D) distribution of magnetic minerals in the Earth’s crust. Almost all rock types contain sufficient magnetic mineral to be ‘seen’ in a modern aeromagnetic survey (concentrations of 0.001% magnetic mineral are usually readily detectable). The magnetic ‘signature’ of a rock unit will be influenced not only by its original composition and environment of formation, but also (and often predominantly) by subsequent events like diagenesis, metamorphism, alteration and weathering. Astute interpretation can ‘read’ some or all of these processes from aeromagnetic imagery. The uniformity of survey sampling and the very frequent continuity of ‘magnetic rock units’, also provides the interpreter with a geometric framework on which structural interpretation can be based. We ‘know all of this’ but often find the task of integrating a high quality set of aeromagnetic imagery and the best available geological information daunting. Where do we start? The Integration Process – Layers In exactly the same way that geological mapping begins, aeromagnetic interpretation starts with a quite basic set of factual observations. We observe and record the locations, shapes and sizes of magnetic rock units and we record pattern discontinuities and trends in much the same way as is done for aerial photography. We produce a ‘factual’ observation layer that can then be directly compared to available geological information, be it factual or interpretive. This leads to a period of integration which very often involves resolving conflicts between the geophysical and geological data. ‘Successful’ integration is usually a slow and painstaking process. It requires the best possible local geological input and an understanding of the way aeromagnetic ‘signal’ relates to the magnetic mineral distribution in the subsurface. It does not require sophisticated software, or indeed any software, if the interpreter so chooses. The outcome of the integration process is a ‘solid geology layer’ that depicts ‘what rocks are where’ and identifies the main fault and fracture patterns. This benefits from further geological interrogation, to consider such things as deformation styles, timing relationships and alteration, metamorphism or mineralisation events. Our third layer in the process is then an integrated, interpretive solid geology. There are many possible extensions and embellishments of this interpretive product including 2-D and 3-D magnetic modelling, production of geological cross sections and integrated 3-D or even 4-D geological models. None of these can be effectively done before the basic, qualitative process of integrating the aeromagnetic imagery and the geology has been solidly preformed. There no shortcuts! 1. Southern Geoscience Consultants, Belmont, WA Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 40 l Ramping-up Exploration Value from Aeromagnetic Surveys – More Geological Input Needed! Golden Dyke Study Area The Golden Dyke example illustrates this integration process in a situation where outcrop is very good, expression of geological features in aerial photography is very good and the area has been well mapped by experienced geologists. The integration of a small amount of aeromagnetic data (200m line spacing amounting to less than 400 line km over a study area of 7km x 10km) in this low grade metasedimentary environment would not be expected to add much to the geological picture- but it does! David Isles extraordinary intensities and may not appear ‘anomalous’ in the geophysical sense, but when integrated with the geology they are very clearly ‘geologically anomalous’. - There are two ‘alteration zones’ definable from their magnetic character. 1. The ‘fuzzy’ magnetic zone in the SW part of the Golden Dyke Dome has a central coherent magnetic low, and looks like a ‘doughnut’. Visual inspection of the aeromagnetic images and consideration of the geological context allows us to propose the nature Figure 1 shows the mapped geology and one of the main images used in the observation and interpretation process. In this study, a set of five key images provided all of the necessary aeromagnetic information. The observation layer is seen as a somewhat messy collection of lines, polygons, measurements and notes. It is very similar to a geologist’s field notes and is indeed the record of our ‘field trip’ to the aeromagnetic imagery. The observation layer is the fundamental initial step in assembling a high quality, high value interpretation. Without this step we run the risk of overlooking much of the subtle information that is often crucial to understanding geological and mineralising processes. The integrated interpretation incorporates an assessment of the regional context, both from published geological studies and the expanded aeromagnetic coverage. It looks, at first glance, very similar to the geology map. We expect this because the geology is well exposed and well mapped. On closer inspection we find a range of quite important additions sourced from the aeromagnetics. - the recognition of magnetic stratigraphic marker horizons in three of the sedimentary units greatly expands our view of the folding and faulting. The clearer and more detailed structural picture is invaluable in the assessment of the area for gold potential. - localised magnetic units in key structural and stratigraphic locations constitute exploration targets. These do not have Figure 1. Geology, aeromagnetic image, aeromagnetic observations and integrated interpretation over the Golden Dyke area, Pine Creek Inlier, NT. The area is 7km x 10km. Geology from the published ‘Batchelor-Hayes Creek’ 1:100,000 scale map, aeromagnetics from the GADDS portal (both sourced from Geoscience Australia) and all images from Isles & Rankin, ‘ Geological Interpretation of Aeromagnetic Data’ (in press). East Asia: Geology, Exploration Technologies and Mines - Bali 2013 41 l Ramping-up Exploration Value from Aeromagnetic Surveys – More Geological Input Needed! of the magnetic mineral distribution and the likely (alteration) mechanism that caused it. We do not need modelling or inversion to do this. 2. The quite subtle zone of decreased magnetic intensity NW of the Golden Dyke Dome (around the Sandy Creek alluvial workings) is not an outstanding feature of the image in figure 1, nor in most of the other images used for the interpretation, but it is consistently identifiable and when considered in its geological (especially structural) context it is likely to be a zone of ‘magnetic mineral destruction’. The new features added from our integration of the aeromagnetics sharpen our focus at the exploration targeting stage. The localised magnetic (geological) anomalies and the alteration zones discussed above are direct and ‘obvious’ target zones, but of equal importance is the refinement of the structural picture, allowing us to apply structural models to the targeting process. If we consider targeting based solely on the (very good quality) geological mapping, the value of the (very small amount of ) aeromagnetic data becomes clear. Mt Leyshon and Bau Districts Two further examples illustrate the stages of observation and integration in different geological environments. David Isles - The Mt Leyshon gold district is ‘a dog’s breakfast’ both geologically and in the aeromagnetic imagery. Integration of the two data sets is a daunting task and one that does not lead to a clear ‘answer’. However, the increased clarity of structure and intrusive ‘zonation’ advances the targeting process significantly. - The Bau gold district in Sarawak (East Malaysia) shows a number of intriguing aeromagnetic features that have not, as yet, been well explained in the context of the known geology. Their possible importance in targeting is conjectural, but addressing the task of integration is very likely to be a valuable step forward in understanding the local geology. Concluding Remarks Significant value is added to an exploration project by the integration of aeromagnetics with geology (and other key data). The integration process is straightforward and qualitative but it requires good geological reasoning and, most importantly, adequate allocation of geologist’s time. The cost of the geologist’s time is small compared to the cost of aeromagnetic data acquisition. The value added to the project by the clearer focus in exploration targeting is the reward for allocation of this time. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 42 l Cu-Au Porphyry System of Atlantis Prospect, Papua Province: A Preliminary Report Hashari Kamaruddin, Hartono, Ciputra. Cu-Au Porphyry System of Atlantis Prospect, Papua Province: A Preliminary Report Hashari Kamaruddin, Hartono, Ciputra. Atlantis exploration project is located in the Star Mountains Range, at the border of Papua New Guinea and Indonesia, in the Papua Province of Indonesia. Mountain Star is the southern flank of the Central Mountain Range along the prospective Papuan Arc Belt. Tectonically, Papua is situated within the Pacific “Rim of Fire”. Geological investigation recorded in Mountain Star was begun by the Dutch agency in 1938 with a gold exploration program then followed by two yearly programs in 1959 and 1961. More systematic exploration was conducted in 1970-1971 by PT. Kenneccot Indonesia with a regional exploration survey. In 1989, PT Ingold Antares acquired the concession in the region, covering some of the Kenneccot survey area. Antam took the tennement in 2008 after PT Ingols Antares return it to the government. The Atlantis project commenced with a due diligence program on some of previously Ingold CHECK concessions in 2008 and literature review and Landsat imagery study. Indicators of mineralisation were interpreted from morphotectonic impression by using SRTM, Landsat and Aster data that allowed the prediction of dilation and elliptical stocks. Follow-up work included (1) compass mapping along streams, (2) creek and ridge traverses documenting with the colour codes “Anaconda” mapping method (3) ridge and spur soil sampling program and (4) ground geophysics acquisition data. The Atlantis Project is situated in the “blank spot interval” between two remarkable deposits of Grasberg and Ok Tedi, in the hihgly prospective mineralisation belt of Papuan Arc. The exploration activities effectively started in the end of 2010 but, unfortunately, had to postpone in the middle of 2012 waiting for forestry permits. The permits are expected to be cleared-up in the middle of 2013. 1. PT Aneka Tambang (persero), Tbk; Unit Geomin, Jl. Pemuda No. 1, Jakarta Timur Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l poster 43 Formation of Advanced Argillic Zones Imants Kavalieris, Khashgerel Bat-Erdene Formation of Advanced Argillic Zones Imants Kavalieris and Khashgerel Bat-Erdene Advanced argillic (AA) alteration forms large tabular zones (or lithocaps), commonly up to several km in strike length and >500 m in thickness. Lithocaps are formed from acid sulfate fluids that may have several origins, including, 1) magmatic-hydrothermal, related to condensation of ascending magmatic volatiles, and 2) steam-heated hot spring alteration, from which acid fluids can descend to deep levels. Similar alteration assemblages, including sulfides can form in both environments, as shown from geothermal studies. Especially in older terrains, poorly exposed and eroded lithocaps are difficult to classify. The main alteration mapping guides to the origin of lithocaps are 1) vertical alteration zonation (mineralogy and texture), 2) nature of the top of the alteration zone (e.g., sinter or fumarolic deposits), and 3) volcanic-intrusive environment. Acknowledgements The authors would like to thank Shawn Crispin, Exploration Manager of PT Agincourt Resources for permission to use data from the Martabe Mine. We are also grateful to our colleagues formerly of PT Intrepid Mines, Adi Maryono, Andrias Kristianto, Bruce Rohlach, Steve Williamson and Rachel Harrison for their support and help, during field mapping at Tujuh Bukit. References Moore JN, Christenson BW, Browne PRL and Lutz SL (2002) The mineralogical consequences of descending acid-sulfate fluids: An example from the Karaha Telaga Bodas geothermal system, Indonesia. Proc 27th Workshop of Geothermal Reservoir Engineering, Stanford Uni California Reyes (1991) Mineralogy, distribution and origin of acid alteration in Philippine geothermal systems, In High-Temperature Acid Fluids and Associated Alteration and Mineralization, Matsuhisa Y, Masahiro A. and J Hedenquist (eds) Geological Survey of Japan Report, 277: 59-65 1. Alteration Mapping Consultants, Plus Minerals Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 44 l Sorting the Signal From the Noise David Lawie Sorting the Signal From the Noise David Lawie1 Modern mineral exploration can avail itself of enormous volumes of data covering a number of disciplines, with additional data constantly being generated on a daily basis during active exploration. This data represents information on ALL the processes that a particular piece of rock or soil has been exposed to. The interpretation of this data is reliant on use of models that describe these processes and the challenge, in a time poor exploration environment, is to define the processes of interest (e.g. evidence of a mineralising event) and separate them from the irrelevant sources, to allow us to make decisions (e.g. drill another hole or walk away) in an efficient way. This paper illustrates the process of sorting the signal (mineralisation) from the noise (everything else) with examples from exploration geochemistry. Exploratory Data Analysis (EDA) methods can be utilised to define for example: • the process by which a signal related to mineralisation is present within surficial materials and then test the data to see if the hypothesis holds, or to • define processes not related to mineralisation (noise) and strip them away so that the signal can be more clearly seen. These are illustrated in the following examples. Surface Exploration in Areas of Transported Cover The uptake of elements from the subsurface by vegetation is one method proposed for the vertical migration of metals through the regolith profile (Aspandiar et al., 2008). Plants have the capability of taking up metals such as Zn, Mo, Se, Au, Ni, Cu As and Pb, storing them and ultimately releasing them to the surface (Aspandiar et al., 2008). The key to confident interpretation of this pattern is defining, in advance, that this migration mechanism is likely to occur and then vector to the source at depth. A good example that illustrates this process is the work of Anand et al. (2007), which tested the use of vegetation in exploring areas of cover in the Yilgarn Craton, Western Australia. Several types of vegetation samples (i.e. litter, roots, etc) were collected in combination with soil samples and then analysed by different methods including total, partial and selective digests. Anomalous Au, As and Mo were detected in several plant organs, with the best anomaly contrast provided by litter samples (Figure 1a, Anand et al., 2007). By defining the hypothesis and rigorously testing it, the movement and accumulation of metals in and by vegetation is demonstrated and so vegetation can be confidently used as an exploration method in this environment. However an alternative approach commonly seen is the fitting of an “interpreted signal” to data collected without consideration of process driving the metal movement and accumulation. This approach often results in incorrectly fitting the signal to random noise (Figure 1b) and the consequent failure to detect mineralisation or the incorrect identification of a false positive. Recognition and Removal of Processes not Related to Mineralisation In complex terrains, simple patterns dominated by the mineralisation process (signal) are rarely observed. The challenge then is to identify and isolate this mineralisation signal from the noise. In other words, our data contains information about both the background and the anomaly and we need to be able to separate them. Sources of noise may include, sampling error, poor program design, analytical error, but also whatever patterns result from geological processes unrelated to mineralisation. A practical example is the analysis of stream sediment data from the Robb Lake Pb-Zn deposit in North-Eastern British Columbia (data from Jackaman, 2008). EDA commonly starts from the simplest observations, in this case by identifying and locating anomalous Zn samples with the aid of univariate plots (Figures 1c and 1d). The next step in the analysis is to understand if these represent true Zn anomalies or if there are factors, other than the mineralization process, that influence the Zn distribution. For example, adsorption by Fe and different background 1. General Manager – Analyitics, ioGlobal Pty Limited, 369 Newcastle Street Northbridge, WA 6003 Australia. Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 45 l Sorting the Signal From the Noise David Lawie Figure 1. concentrations in different lithologies influencing the Zn distribution. A simple scatter plot of Zn vs Fe allows us to quickly test and confirm whether Fe adsorption is occurring. A regression analysis of Zn on Fe is then undertaken to identify Zn residuals (i.e., Zn not controlled by Fe) which then can be visualised spatially (Figures 1e and 1f ). This is an example of how the signal (the Zn anomaly) can be enhanced by removing the noise (Zn related to Fe content). A similar process can be applied to test if Zn is also controlled by geology. In this case a regression analysis, subdivided by geological group, can be undertaken to remove the effect of geology on the Zn distribution (Figure 1g and 1h). A completely different anomalous population is now identified compared to just picking the highest values in the raw data. References Anand, R., Cornelius, M., and Phang, C. (2007): Use of vegetation and soil in mineral exploration in areas of transported overburden, Yilgarn Craton, Western Australia: a contribution towards understanding metal transportation processes; Geochemistry: Exploration, Environment, Analysis, Vol. 7 2007, pp. 267–288. Aspandiar, M.F. Anand, R. and Gray, D. (2008): A review of mechanisms of metal dipersion through transported cover: implications for mineral exploration in Australia; CRC LEME open file report, 246 p. Jackaman, W. (2008): Regional Stream Sediment and Water Geochemical Data, Pine Pass (NTS 93O), British Columbia; Geoscience BC, Report 2008-7, 262 p. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 46 l Biogeochemistry and Partial Digest Techniques in Mineral Exploration – a Brief Review Evgenia Lebedeva, Andrew Riley Biogeochemistry and Partial Digest Techniques in Mineral Exploration – a Brief Review Evgenia Lebedeva1 and Andrew Riley1 The development of analytical instrumentation has expanded opportunities for low level geochemistry and its application in mineral exploration. There is growing interest to such techniques as biogeochemistry and partial digest. Difficulty with the interpretation of data from these methods often prevents people from using them in exploration; however, these methods could be very useful when exploring blind or buried mineralization. Such geochemical techniques combined with ground magnetic surveys, AEM conductivity, hyperspectral data etc. can significantly improve drill targeting. Biogeochemistry is particularly useful as a guide to the underlying geology in areas of transported cover, where the signature in the vegetation can be better than the soils1. In arid and semi-arid conditions, due to greater root:shoot ratios2 in vegetation, roots can penetrate several meters in depth to reach the permanent water source. For example, roots of Spinifex have been observed in mine pits at depths of 30 m and below3. In tropical forests roots can penetrate up to 18 m deep, while tropical grassland can penetrate even deeper (up to 68 m)2. There is very limited open data on biogeochemistry exploration in East Asia. It was found that species of genera Homalium and Hybanthus were identified as hyperaccumulators of nickel and can be used as an indication of nickeliferous (usually ultrabasic) rocks4. These plants are abundant in Indonesia, in particularly on Sulawesi and Halmahera Islands. In ultramafic areas, such as Sabah (Malaysia) and the Philippines, the strong nickel hyperaccumulator is Phyllanthus balgooyi. For Au investigations in equatorial regions Astronidium palauense, a moderate size tree, is widely distributed in the region and can be successfully used in biogeochemical exploration5. In the Amazon region (Carajas) geobotanical remote sensing showed that distribution of vegetation correlated with variations in geology6. About 200 published scientific studies on biogeochemistry in Australia were analysed at Intertek Genalysis. The majority of studies (46 %) were devoted to identify Au mineralization. In studies for Au mineralisation the major plant tissue were leaves and leaflet branchlets (87%), bark (7.8%), twigs (3.1%) and litter (1.6%). Bark and leaves on average gave the highest values for gold anomalies. The most popular species successfully used in exploration studies Fig.1. Example of samples media that can be collected for biogeochemistry (leaves, bark, litter and roots) and partial digest (soil). in Australia are Acacia and Eucalyptus, Spinifex, Tea tree, Fuschia bush, Monterey pine, Black oak and Cassinia. Several companies with reports published on the ASX used biogeochemical sampling techniques to identify drill targets, to name a few – Australasian Resources Ltd used vegetation sampling to identify Ni mineralization7, Marmota Energy Ltd used vegetation to identify U mineralisation8, PepinNini Minerals Ltd used Spinifex to target Ni/Cu and base metal mineralisation9, Blaze International Ltd applied biogeochemistry to target calcrete-hosted and granitehosted U mineralisation10, Cullen Resources Ltd used vegetation to delineate base-metal mineralisation11. Partial digest techniques are also used to detect trace element concentration in the top soil profile, avoiding complete digest of silicate, iron or calcium-rich minerals. Complete dissolution of such minerals results in high TDS (total dissolved solids) content, increasing detection limits for the trace elements of interest (for example Ag and Au), which could be associated only with minor fractions (like 1. Intertek Minerals, Jakarta, Indonesia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 47 l Biogeochemistry and Partial Digest Techniques in Mineral Exploration – a Brief Review clay or organic fractions). Partial digests enable preferential high recovery of these ions in comparison to poor recovery of ions that are lithologically sourced and more tightly bound on the mineral surface. A number of companies have successfully utilised Partial Digests in exploration. Gold Road Resources utilised partial leaching techniques over Permian cover in areas with no previous drilling. The partial leach was performed on -75 micron soil fraction of the top soil profile and this appeared to be more effective than conventional digest12. Trafford Resources Ltd successfully used partial digests together with a geophysical exploration program13 (the soil was taken within top 20 cm) to identify IOCG (Iron Oxide/Copper/ Gold) target while Investigator Resource Ltd was successful in utilising partial digest to delineate silver mineralisation14. References Evgenia Lebedeva, Andrew Riley 2. Canadell, J. et al, 1996. Maximum rooting depth of vegetation types at the global scale. Oecologia, 108, pp. 583–595. 3. Reid, N., Hill, S., Lewis, D., M., 2008. Spinifex biogeochemical expressions of buried gold mineralisation: The great mineral exploration penetrator of transported regolith. Applied Geochemistry, 23, pp. 76-84. 4. Brooks, R.R. et al. 1997. Detection of nickeliferous rocks by analysis of herbarium specimens of indicator plants. Journal of Geochemical Exploration. 5. Mclinnes, B. I.A. et al. 1995. Biogeochemical exploration for gold in tropical rain forest regions of Papua New Guinea. Journal of Geochemical Exploration. 6. Paradella, W.R. et al, 1994. A geobotanical approach to the tropical rain forest environment of the Carajas Mineral Province. International Journal of Remote Sensing, Vol. 15, 8, pp. 1633-1648. 7. ASX Announcement 30 July, Australiasian Resources Ltd. 8. ASX Managing Director’s Presentation, Marmota Energy Ltd. 9. ASX Financial Report 31 December 2010, PepinNini Minerals Ltd. 10.ASX Announcement 31 January 2012, Blaze International Ltd. 1. Anand, R.R., Cornelius, M., Phang, C. Use of vegetation and soil in mineral exploration in areas of transported overburden, Yilgran Craton, Western Australia: a contribution towards understanding metal transportation processes. Geochemistry: Exploration, Environment. Analysis, 7, pp. 267-288. 11.ASX Announcement 28 November 2011, Cullen Resources Ltd. 12.ASX Announcement 22 November 2012, Gold Road Resources Ltd. 13.ASX Announcement 14 March 2012, Trafford Resources Ltd. 14.ASX Presentation 7 December 2012, Investigator Resources Ltd. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l poster 48 Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik, Ferdian Haryadi, Gita Srikandi Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik1, Ferdian Haryadi1, Gita Srikandi2 The research area is administratively located on Conggeang Distric, Sumedang Regency, West Java Province. Physiographically, the research area is located between Bogor Zone and Quaternary Volcanic Zone. Stratigraphy units of the research area are divided into three lithological units, from old to young, i.e., Claystone Unit, Volcanic Breccia Unit and Andesitic Unit. Geothermal systems have three important elements, i.e., reservoir, fluids, and heat sources. The Geothermal systems in the research area triggered by volcanic activity associated with Quaternary volcanism and magmatic intrusion.The geothermal fluid type is mixing between chloride water and bicarbonate water. Located in the outflow zones whit high relief. Reservoir temperature between 200-210⁰C. The Geothermal systems is flowing through fracture and cause alteration in the surface of research area that form of sinter travertine, vein and kaolinite. Figure 1. Geological map at geothermal research area, Conggeang Area, Sumedang Regency, West Java. Regional Geology According to Bemmelen (1949), physiographically, West Java region divided into four zone which has west-east trending, i.e., Jakarta Beach Plain, Bogor Zone, Bandung Zone, and Southern Mountains Zone. Research area is located in the boundary between Bogor Zone and Volcanic Quaternary Zone. Eastern slope of Tampomas Maountain, also the western side of Arjawinangun Sheet (Djuri, 1973). Research area is located at high topography with elevation range 625 – 1.684 meter above sea level. Regionally, research area has Java pattern stress (Fig 3). There is thrust fault, dextral strike slip and anticline at the south east of the research area. Thrust and fold relatively has north westsouth east trending, which occur in Subang Formation and other sediment tertiary. Young tectonic activity showed by two trend of fault, north-south trending to north east-south west (NNE-SSW), which cross cut Tampomas Mountain volcanic sequence, but both fault not related to any thermal activities. Figure 2. Physiographic of West Java, the research area is located at the boundary between Bogor Zone with Quaternary volcanic zone (Bemmelen, 1949 in Martodjojo, 1984) Regional Stratigraphy Research area located between Arjawinangun and Bandung sheet. Lithological unit from younger to older are (Fig 4): 1. Alluvial 2. Young Volcano Product consist of lava (Qyl) and disheveled volcanic rock (Qyu) 1. Departemen Teknik Geologi Insitut Teknologi Bandung Corresponding author: [email protected] 2. PT.PERTAMINA East Asia: Geology, Exploration Technologies and Mines - Bali 2013 49 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik, Ferdian Haryadi, Gita Srikandi 3. Old Volcano Product consist of lava (Qvl), breccia (Qvb), disheveled volcanic rock (Qvu). 4. Citalang Formation (Pt), consist of bedding of tufaceous sandstone, conglomerate, and tufaceous claystone 5. Kaliwangu Formation (Pk), consist of tufaceous sandstone, conglomerate, claystone, and bedding of calcareous sandstone 6. Subang Formation, consist of claystone, marl, and limestone. Geological Setting Stratigraphy There are three lithological units in the research area, which are Claystone Unit as the oldest rock unit, Volcanic Breccia, and Andesite as the youngest rock unit. Figure 3. Regional stress pattern on Java Island, the research area is located in the Java pattern (modified from Punggono and Martodjojo, 1994) Claystone Unit Claystone Unit is composed of Claystone lithology with intercalation of tuffaceous sandstones. The unit’s appearance in the field characterized by grey colored claystones, calcareous, massive, have been undergoes conchoidal weathering, and can be found nodules in some area (Image 2). According to petrography analysis, claystones in this unit containing calcite, small foraminifera shell’s shards, and glass shards. Micropaleontology analysis showed that this unit was Upper Miocene Aged (N16 - N 18) based on Blow Biozone (1969). Volcanic Breccia Unit Appearances of this unit characterized with volcanic breccia with intercalation of lava flow and piroclastic. Breccia with brown color, grain size of gravel to cobble, poor to medium sorted, angular to sub-angular rounded, clay to sand matrixed, non-calcareous cement, basalt fragment, andesite, crystalline tuff, compact, open fabric, poor porosity (Image 1). Has a spotted claystone matrix with a rounded to sub-rounded grain shape. According to petrography analysis, fragments inside the breccia contain crystalline tuff, pyroxene andesite, and basalt. Pyroxene Andesite Unit This unit appearance in the field characterized by bright grey colored andesite, aphanitic-porphyritic with pyroxene as fenocryst inside smooth matrix, massive (Image 3). Based by petrography observation, the andesite that found in the research area is a pyroxene andesite with plagioclase microlite dominated matrix. Geological Structure Geological structure that existed in the research area is Cipicung fault and Cikujang fault. Figure 4. Arjawinangun Stratigraphic Cikujang Fault The fault that cut the breccia unit and the claystone unit observed by brecciation appearance off set contact between breccia unit and claystone unit. The brecciation that lay on the Cikujang River’s Cliff heading towards main direction N 213 E. Based on structural analysis (Fig 6), Cikujang fault is a right lateral-normal fault with N 330 E/730 strike and dip fault plane. Cikujang fault contain breccia alteration that altered to clay mineral. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 50 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik, Ferdian Haryadi, Gita Srikandi Cipicung Fault Cipicung fault at Cipicung River observed based on shear appearance on the riverside. Beside, fault existence can be shown by the offset contacts between claystone unit and breccia unit with an approximately 10 meters long so the fault cut the claystone unit and breccia unit. Apart from the existence of shear, there is also N 93 E brecciation trending. Based on structural analysis (Fig 6), Cipicung fault is a right-lateral-normal fault with N 95 E/58 strike and dip fault plane. Similarly as Cikujang fault, Cipicung fault also contain breccia alteration that altered to clay mineral. Geothermal System Geothermal system has three important elements which are: reservoir, fluid, and heat source (Goff and Janik, 2000). Characteristic from this geothermal system’s elements determined by water-chemical analysis from three water samples that taken from the field, those are: Cipanas 1, Cipanas 2, and Cileungsing which are a hot water manifestation from the geothermal system around the research area. Figure 5. Mudstone unit profile at Cikujang River, indicate a change in lithology and sedimentary patterns due to changes in the environment Geothermal Fluid Type Based on Cl, SO4, and HCO3 anion, hot water type in the research area is a chloride-bicarbonate and bicarbonate (Figure 8). Cipanas-1 sample derived from seepage along Cipanas River that coming out through a fracture at the volcanic breccia. Cipanas-1 hot water is dominated by HCO3 anion (bicarbonate). Cipanas-2 classified as a bicarbonate water (HCO3) that dominated by HCO3 anion. Cileungsing’s water sample classified as a chloridebicarbonate because the water consist a higher chloride concentration which is 635.30 mg/L compared to HCO3 (519.50 mg/L) and SO4 (2.22 mg/L). Cileungsing’s hot water is predicted derived directly from the geothermal reservoir under the surface although it is affected by HCO3 (bicarbonate) and sulfate (SO4) ion. Reservoir and Source Relatively higher Cl concentration compared to Li and B (Fig 9) showed that the hot water in the research area came from the same reservoir and affected by volcano-magmatic activity. And the high concentration of Mg-44 to 60 ppm-in the research area showed that there been a mixing between geothermal fluid and ground water near the surface. Figure 6. The kinematics analysis and faults dynamic that show common patterns of fault is dextral-down and down-dextral in the research area East Asia: Geology, Exploration Technologies and Mines - Bali 2013 51 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik, Ferdian Haryadi, Gita Srikandi Hot Water Flow Pattern Bicarbonate water type that present showed that the fluid reservoir had been condensed and mixed with surface water. This thing indicate that the hot fluid undergo lateral flow (outflow zone). Figure 9 shows that the hot water in the research area contains high Cl concentrate compared to B and Li. This thing shows that the hot water affected by volcano-magmatic activity. Comparison of Na/K and K/ Mg that showed by Fig 10 indicate that three of the spring is inside the outflow zone. By that we can conclude that in this area occur a reaction between hot water, ground water, and rocks near the surface. According to Hochstein and Browne (2000), volcanogenic manifestation which present in the geothermal system is highly affected by reliefs and topography of the volcano (Fig 11). At the top of area, manifestation that present can be a fumarole and solfatara that consists uncondensed steam and gas. Beside, manifestation that could possibly present is sulfate spring which is a result from a steam condensation that mixed with shallow meteoric water so H2S oxidized become H2SO4. Chloride water is located deeper than sulfate water (Hochstein and Browne, 2000). Because of the topography and hydrology gradient chloride spring usually found far from the heat source and the main reservoir. Thus, on the geothermal system in the research area is a high relief in a form a mountain range, chloride water will be found in the outflow zone, not in the up flow zone like a plain relief geothermal system. Conceptual model that describe the emersion of surface manifestation can be used as a reference to knowing Tampomas Mountain’s geothermal system. Surface manifestation present in Tampomas Mountain foothill took form in a bicarbonate and chloride-bicarbonate hot spring at the outflow. Referring to the conceptual model, chloride water that came directly from the reservoir is possibly located in Tampomas Mountain foothills which has lower elevation and farther than the peak. Thus, to get chloride water sample that directly came from the reservoir and haven’t mixed with the ground water can be done in the foothills. Image 1. Breccia vulcanic unit at side of cipanas stream, poor sorted Image 2. Claystone unit Manifestation location that took form of warm-chloride water spring might be located a few kilometer from the warm water manifestation that being currently observed. Hot Water Isotope This study is only observes a stable isotope concentrate. Stable isotope that generally used in geothermal study is hydrogen isotope (1H, 2H or D-deutrium), carbon (12C, 13C), oxygen (16O, 18O), and sulphur (32S, 34S). Those isotopes used for knowing the processes or the origin of water or gas. δD content on geothermal fluid is the same as δD that consist in meteoric water. On the other hand, the value of δ18O on geothermal fluid will be more positive compared to meteoric water (Craig, 1956; Craig, 1963 in Nicholson, 1993). Alteration of δ18O value is caused by an exchange reaction with a heavier isotope. Image 3. Andesite stone unit Some of the isotope value shows that magmatic-fluid contribution on geothermal fluid is minor (5 to 10 percent from total) while the rest derived from meteoric water. The effect of magmatic fluid will show geothermal fluid δD value will not be the same with meteoric water δD value (Nicholson, 1993). Stable isotope that used for warm water sample in the research area is D-Deutrium and 18O. Both isotope values are used to finding out that the East Asia: Geology, Exploration Technologies and Mines - Bali 2013 52 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik, Ferdian Haryadi, Gita Srikandi Figure 7. Map of sampling location hot fluid in the geothermal system in the research area is derived from meteoric water or magmatic fluid. Based on deuterium isotope and Oxygen-18 value (Table 2), all three of the hot spring located around the blue line which is a global meteoric water line (Fig 12). This shows that the geothermal system at Tampomas Mountain recharge from meteoric water. Geotermometer Geotermometer is a method to calculate fluid temperature in the reservoir. Geotermometer that used were adjusted with character of the geothermal system. Reservoir fluid temperature has error tolerance up to 10⁰C. Based on temperature, the geothermal system can be divided into three categorize, those are: high temperature geothermal system (T ≥ 2500C), medium temperature geothermal system (T=125-250⁰C), and low temperature geothermal system (T ≤ 125⁰C). High temperature geothermal systems generally associated with volcano activity. Temperature can reach ≥ 2000C (Hochstein and Browne, 2000). Thus, geotermometer that suitable with high temperature is K-Na geothermal and Si02, because the geotermometer is valid with high temperature condition (Nicholson, 1993). Formulas for the calculation of K-Na geotermometer are: toC = 1217/ [log (Na/K) + 1.483] – 273 (Fournier, 1979 in Nicholson, 1993) toC = 1390/ [log (Na/K) + 1.750] – 273 (Giggenbach, 1988 in Nicholson, 1993) The geotermometer have some limitation, those are: 1. Used for water that has >180 0C reservoir temperature. Image 4. A. Cipanas-2 Warm Pool B. Cileungsing Hot Pool C. Springs 2. Used if water contain low Ca based on the calculation (log (Ca1/2 / Na) + 2,06) and the result is negative. 3. Used to chloride water approach neutral pH. Silica geotermometer used were adiabatic quartz geotermometer and conductive quartz. The formulas for this two geotermometer are: Adiabatic Quartz (Maximum Steam Loss): toC = 1522/ (5,75-log SiO2) – 273 (Nicholson, 1993) East Asia: Geology, Exploration Technologies and Mines - Bali 2013 53 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik, Ferdian Haryadi, Gita Srikandi Conductive Quartz (No Steam Loss): toC = 1309/ (5,19-log SiO2) – 273 (Nicholson, 1993) Quartz geotermometer is useful for the > 1500C reservoir temperature condition. For example geothermal system that were triggered by magmatic activity. This geotermometer also have some limitation, those are: 1. Adiabatic quartz geotermometer useful for well and boiling hot spring or pond with ≥ 2 kg/s water discharge especially 50 that have sinter silica. Maximum temperature has been calculated by this geotermometer for spring manifestation is ~ 2100C. 2. Conductive quartz geotermometer useful for sub-boling temperature spring. Hot water type that can be used for geotermometer calculation is chloride water type (Cl), because chloride water has pH of about neutral which has the best condition to shows the reservoir condition. In the research area, geotermometer only used for Cileungsing hot water, because that area is the only place which has Cl anion dominated rather than HCO3 and SO4 anion. Table 1. The results of chemical analyzes of water sampling Cipanas-1, Cipanas-2 and Cileungsing Based on geotermometer calculation, the temperature we got are about 200-2100C from K-Na geotermometer and 1050C from conductive quartz geotermometer. And based on some K-Na geotermometer requirement, with (log (Ca1/2/Na) + 2,06) = -1,9 and silica geotermometer, the most suitable geotermomter is K-Na geotermometer with 200-2100C reservoir termperature. Thus, fluid reservoir temperatures at Tampomas geothermal system are about 200-2100C. Surface Alteration Alteration in the research area can be found at Cipanas River and fault zone. At Cipanas River, the alteration existed around hot water manifestation, especially at the edge of fracture which hot water coming through. At the fault zone, alteration in a form altered matrix and fragment volcanic breccia. Matrixes altered become white and bluish grey colored clay mineral. Hot Water Seepage at Cipanas River Figure 8. The type of geothermal fluid is water mixturing between chloride water with bicarbonate water Hot water seepage around Cipanas River were associated with fracture existence at Volcanic Breccia Unit (Image 5). This seepage caused the breccia were undergoing altered, not only at the surface but also in the matrix and its fragment. Unlike the other breccia, this altered breccia East Asia: Geology, Exploration Technologies and Mines - Bali 2013 54 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Figure 9. Comparison of B, Li and Cl indicate warm water in the research area associated with the activity Sony Malik, Ferdian Haryadi, Gita Srikandi Figure 10. Comparison of the relative content of Na-K-MG showed warm water in the research area is an immature water Figure 11. Conceptual Model geothermal system triggered by andesitic stratovolcano Table 2. Isotope values of detrium and oxygen-18 East Asia: Geology, Exploration Technologies and Mines - Bali 2013 55 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency had some character, those are red colored at the surface that contact with hot water, also had calcite vein with 0,1-0,5 cm width and 5-20 cm long that filled the fracture and weak plane between matrix and fragment Breccia outcrop that found around the hot spring relatively more compact compared to the other breccia and relatively had close fabric which contact with hot water. Hot Pond Sony Malik, Ferdian Haryadi, Gita Srikandi Table 3. The temperature of the reservoir based on the calculation of various geotermometer Hot pond at Cipanas Riverside form naturally and left sinter travertine residue (Image 9). This travertine has white colored, smooth texture, and lamination shows that the depositional happen iteratively. Massive and compact is the main character of this deposit. Fault Zone Alteration There is altered rock become white and grey at the area around fault (Image 10). Those altered rock consist of variety of mineral, like quartz, albite, analsime, and kaolinite. Kaolinite existence indicated that altered processes in acid pH condition (Lawless, 1993). Alteration and Geothermal Pattern Altered process that occurred at the research area caused by hot water coming through along fractures. Those showed by contact of hot water and made the appearance of breccia become altered. Whereas alteration pattern at the fault zone also associated with fracture that caused hydrothermal flow at the fault zone even though weren’t found hot water manifestation at the fault zone. Figure 12. Shows the source of the fluid in the research area derived from meteoric water Image 5. A. infiltration of warm water from the river through the cracks B. Some of the hot springs in the riverbed (G11.14) Existence of kaolinite mineral at the fault zone indicated this alteration pattern. Manifestation and alteration at the research area in a form sinter travertine and calcite vein. Both of this product alteration is composed by calcite. The differences between this two are subsurface formed for calcite vein, while sinter travertine formed at the surface. Two of this mineral will form at CO2 rich condition based on the reaction: Ca2+ + CO2 +H2O → CaCO3 + 2H+ This reaction also showed that calcite (CaCO3) will occur if Ca2+ rich and react with CO2. Kaolinite is alteration mineral that formed at acid condition (Lawless, 1993). While sinter travertine is surface deposit that formed relatively more alkali condition compared to kaolinite (Nicholson, 1993). Those two manifestations showed that there is a change of fluid character at the research area. Acid conditions become more alkali. Kalonite existence which Image 6. Calcite veins in volcanic breccia at Cipanas Stream (G11.12) East Asia: Geology, Exploration Technologies and Mines - Bali 2013 56 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Sony Malik, Ferdian Haryadi, Gita Srikandi occurred at acid pH conditions could cause by condensation process at the steam zone. Condensation near the surface caused H2S oxidized became H2SO4 and pH rises. In addition, kaolinite existence also associated with claystone lithology at the research area. Conclusion 1. Stratigraphy at the research area those are Claystone Unit Upper Miocene aged (N16-N18), Volcanic Breccia, and Pyroxene Andesite as the youngest rock unit. 2. Geological structure that existed in the research area is Cipicung right-lateral normal fault and Cikujang normal fault. This two of fault occurred in one phase of deformation. 3. Geothermal fluid types are mix of chloride water and bicarbonate. 4. Research area is an outflow zone. Kaolinite existence also showed lateral flow and formed at CO2 rich condition at the atmosphere. Image 7. Thin section of vulkanic breccia matrix with calcite vein filling fracture (G11.12) 5. Tampomas geothermal reservoir temperatures are about 200-210⁰C. This high temperature geothermal system generally associated with volcano activity. 6. Altered process that occurred at the research area caused by hot water coming through along fractures. Manifestation and alteration at the research area in a form sinter travertine and calcite vein. Those two manifestations showed that there is a change of fluid character at the research area. Acid conditions become more alkali. References Bemmelen, R.W. van, 1949, The Geology of Indonesia, Martinus Nyhoff, The Haque, Nederland Blow, W.H., 1969, Late Middle Eocene to Recent Planktonic Foraminifera Biostratigraphy. Proceedings First International Conference on Planktonic Microfossils, Geneva Hochstein, M. P. and Browne, P. R. L., 2000, Surface Manifestations of Geothermal Systems with Volcanic Heat Source. In Encyclopedia of xiv Volcanoes (editor: Sirgudsson, H., Houghton, B., McNutt, S. R., Rymer, H., Stix, J.), Academic Press, San Diego Image 8. Thin section of travertine sinter deposite on vulcanic breccia (G11.15) Lawless, J. V., 1993, Epigenetic Magmatic-Related Mineral Deposits Exploration Based on Mineralization Model, Kingston Morrison Mineral Services, Auckland Martodjojo, S., 1984, Evolusi Cekungan Bogor, Jawa Barat, ITB Press, Bandung Muhardjo, Nasution, A., Yusup, R. dan Yuhan, 1985, Laporan Penyelidikan Geologi Daerah Panasbumi Gunung Tampomas, Kabupaten Sumedang, Jawa Barat. Volcanology Directorate, Bandung Nicholson, K., 1993, Geothermal Fluids Chemistry and Exploration Techniques, Springer Verlag, German Image 9. Travertine Sinter deposite at side of hot pool (G11.15 location) East Asia: Geology, Exploration Technologies and Mines - Bali 2013 57 l Geothermal Surface Manifestation and Alteration of Conggeang Area, Mount Tampomas, Sumedang Regency Image 10. Alterated rock at G7.3 location, white colour Figure 13. Geothermal system model in research area (without scale) East Asia: Geology, Exploration Technologies and Mines - Bali 2013 Sony Malik, Ferdian Haryadi, Gita Srikandi 58 l Porphyry Copper-Gold Mineralization Styles along the Eastern Sunda Magmatic Arc, Indonesia Adi Maryono, Rachel Harrison Porphyry Copper-Gold Mineralization Styles along the Eastern Sunda Magmatic Arc, Indonesia Adi Maryono1 and Rachel Harrison2 Porphyry mineralization has played a significant role in contributing gold, silver and copper endowment to the 1,800km E-W striking Eastern Sunda Magmatic Arc, part of the 3,940 km-long Sunda-Banda Arc (Setijadji et al. 2006, Maryono et al. 2012). With a world class goldsilver-copper endowment currently estimated at 92.44 million ounces of gold, 279.17 million ounces of silver and 61.92 billion pounds of copper, the Eastern Sunda Magmatic Arc has emerged as one of the most prospective gold-copper belts in the world. The recently discovered world-class porphyry deposit at the Tujuh Bukit Project with 30.1 million ounces of gold and 19 billion pounds of copper (Intrepid Mines Ltd., 2012) has now joined two known world-class copper-gold deposits at Batu Hijau and Elang to confirm the Eastern Sunda Arc as an emerging, economically important magmatic belt. Other known porphyry prospects and related epithermal prospects identified along the belt offer promising future resource potential. Three world-class porphyry Cu-Au deposits at Batu Hijau, Elang and Tujuh Bukit and high sulfidation epithermal deposits at Pangulir, Sane, Gapit, Sabalong, Pelangan, Mencanggah and Tujuh Bukit (Oxide Zones) are tectonically confined to the eastern segment (East Java to Sumbawa) that was constructed on thinner island arc crust bounded by Australian continental crust further east in Sumba and Timor (Hamilton, 1979; Carlile and Mitchell, 1994; Hall, 2002; Setijadji et al., 2006; Maryono et al. 2012). In contrast, the sub-economic porphyry prospects at Selogiri, Ciemas and Cihurip with dominant low sulfidation epithermal deposits at Pongkor, Cikotok, Cibaliung, Cikondang and Arinem occur in the western segment of the arc (West to East Java) that developed on thick continental crust on the southern margin of Sundaland. The whole metal endowment of the Eastern Sunda Arc is related to the Neogene magmatic stage, one of 5 stages of magmatic activity identified along the belt. Dating of mineralization age and/or related intrusion age shows similar features to the magmatic host rocks where mineralizing intrusions have been dated as Neogene in age, 3.7 Ma at Batu Hijau, 2.7 Ma at Elang, 7.5 Ma at Selodong, 2.5 Ma Figure 1. The Eastern Sunda Magmatic Arc with three world classporphyry Cu-Au deposits discovered along the belt, making it one of world’s most prospective magmatic belts. at Pongkor and 3.0 Ma at Arinem (Marcoux and Milési, 1994; Garwin, 2000; Maryono et al. 2005; Roe pers. com, 2012; Yuningsih et al., 2012). This is consistent with the Western Pacific region where the largest gold endowment (about 45.1% or 321.2 million ounces) is hosted in Neogene magmatic arcs (Maryono and Power, 2009). In spite of similarities to those in typical island arc settings, e.g. the Philippines, PNG, Solomon Islands and Fiji, porphyry gold-copper mineralization styles in the Eastern Sunda Magmatic Arc display some unique characteristics. Coppergold mineralization is spatially and temporally developed within and around small, multiple, nested, tonalitic porphyry intrusions (<1km2 with +1km vertical extent) as apophyses to precursor underlying large, more equigranular texture, dioritic intrusive bodies (+4 km2). Intrusion ages range from 2.7 Ma at Elang, 3.7 Ma at Batu Hijau to 7.5 Ma at Selodong with latest intrusive activity marked by postmineralization diatreme breccia bodies which are developed at the margin or adjacent to the porphyry systems and disrupt the mineralized bodies. Host stratigraphy is generally characterized by Miocene volcanic rocks and associated volcaniclastic rocks as a volcanic edifice. The volcaniclastic rock sequence contains thin calcareous sedimentary rocks and limestone, which form thin skarn mineralization, e.g. at Elang, Batu Hijau and Tujuh Bukit. 1. PT Buena Sumber Daya, Jl. Radin Inten II No 2, Buaran Duren Sawit Jakarta Timur Corresponding author: [email protected] 2. Independent Geologist, Sading, Sempidi ,Badung Bali. Email:[email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 59 l Porphyry Copper-Gold Mineralization Styles along the Eastern Sunda Magmatic Arc, Indonesia Hypogene mineralization at the three world-class deposits, as marked by the 0.3% Cu zones in surface projections of drill hole data, measures on average more than 1 km in diameter and around 1km vertical extent. Hypogene alteration, veining and sulfide mineralization developed in three main temporally and spatially overlapping events, termed as Early, Transitional and Late (Mitchell et al. 1998, Clode et al. 1999, Maryono et al. 2005 and Harrison, 2012). The gold and copper mineralization is directly related to quartz veining, classified as “A’,”A-family”, “EDM”/”EB”, “B”, “C” and “D” of Gustafson and Hunt, 1975, Brimhall, 1977 and Clode et al., 1999 .The copper-gold mineralization forms an annular or inverted shell that lies within and around the margins of tonalite intrusive bodies. The Early “A” veins contain the bulk of hypogene chalcocite, digenite, bornite solid solution (chalcocite-bornite and digenitebornite) and bornite. These veins are estimated to constitute majority of quartz veins and copper content in the deposits. The transitional veins (“B” and “C”) contain chalcopyrite with minor or trace bornite. Bornite and chalcopyrite are the dominant copper sulfide minerals which form sulfide zones, namely a central bornite dominant core, large chalcopyrite-dominant middle zones and marginal pyrite shells. Supergene copper mineralization is limited, developed beneath goethitic leached caps only at Batu Hijau and Elang. A weak chalcocite blanket averaging 40m thick and 0.5 to 0.7 % Cu has been intercepted in drill holes. The copper enriched zone measures in excess of 500m by 750m in plan view with variable thickness and is characterized by an overlying goethite-hematite leached cap at the surface. Very thin supergene copper mineralization (0.3 to 0.5% Cu, 10 to 20m thick) has been intersected at Brambang but does not form a significant chalcocite blanket. Porphyry mineralization in the Eastern Sunda Arc is typified by gold-rich porphyry systems with only Tujuh Bukit having significant molybdenum content (90 ppm) at 0.2% cut-off. Majority of gold was deposited during the formation of early “A”, ‘A-family” and “EDM/EB” veins and is dominantly associated with bornite rather than chalcopyrite (Clode et al., 1999, Arif and Baker, 2004; Maryono et al., 2005 and Harrison, 2012). Gold mostly occurs in bornite-rich ores within copper sulfide grains as invisible gold and other forms along quartz-silicate grain boundaries as native gold or free gold. The native gold grains are generally 1 to 12 µm. Higher free gold abundance develops in chalcopyrite-rich ore than bornite-rich ore (Arif and Baker, 2004). It’s similar to other gold-rich porphyry systems e.g. Alumbrera and Cadia. Adi Maryono, Rachel Harrison (+20 km2) as a product of late alteration events above porphyry mineralized centers. The large lithocap bodies have undergone various erosion intensities to expose porphyry deposits from very shallow or totally preserved at Hu’u, Brambang and Tujuh Bukit to deeply eroded at Batu Hijau and Elang. High sulfidation epithermal gold-silver mineralized systems are developed within lithocap bodies associated with quartz ledges at Elang, Brambang and Oxide Zones of Tujuh Bukit to form a telescoped system. Biotite and shreddy chlorite (chlorite after secondary biotite) are the dominant alteration minerals in ore-bearing alteration zones. Actinolite is an important alteration mineral as part of orebearing alteration assemblages along with biotite, chlorite, oligoclase, k-feldspar and magnetite which develop during early phase hydrothermal events. Abundant shreddy chlorite, actinolite and minor or lack of k-feldspar marks notable differences with regards to alteration at other deposits. Zones of early alteration contain porphyry vein types “A”, “EB”/’EDM” and “A-family” with dominant chalcopyrite and bornite mineralization. References: Arif,J. and Baker, T. 2004, Mineralium Deposita; 39, 523-535, Brimhall, G.H., Jr., 1977, Econ. Geo. 72, 37-59 Carlile, J.C., Mitchell, A.H.G., 1994, Jour. Of Geochemical Explor., 50, Clode, C.H. et al. 1999, Proc. Pac-Rim Cong, 485-498 Garwin, S., 2002, Indonesian Society of Economic Geologists, Special Publication 9: 333-366 Guilbert, J.M., Park Jr., C.F., 1986, The Geology of Ore Deposits, W.H. Freeman and Co., NewYork Gustafson, L.B. and Hunt, J.P., 1975, Economic Geology 70, 857-912 Hamilton, W.B., 1979, Professional Paper 1078, U.S. Geol. Surv., Washington, DC, 345 Hall, R., 2002, J. Asian Earth Sciences, 20: 353-431 Harrison R.L. 2012, MGEI Proc 4, 89-90 Intrepid Mines Ltd, 2012, Intrepid Mines Limited: http://intrepidmines. com.au/investor-relations/news-and-announcements Marcoux, E. and Milési, J.-P., 1994, J. Geochem. Explor. 50, 393-408 Maryono, A. et al.2005, IAGI Indonesian Minerals and Coal Discoveries, Maryono, A. and Power, D., 2009, Maryono et al. 2012, MGEI Proced 4, 23-30, Mitchell et al. 1998 Inter PT Newmont Nusa Tenggara report, 164pp, Newmont Mining Corporation, 2012, http://newmont.q4web.com/files/doc_presentations/ Diggers & Dealers.pdf Setijadji, L.D. et al, 2006, Resource Geology 56 (3): 267-292 Ulrich T and Hendrich C.A. 2001, Econ. Geo. 96, 1719-1742 Yuningsih et al. 2012, Resource Geology 62 (2); 140-158 Surface alteration at district to deposit scale is typically manifested by large overlying lithocap alteration bodies East Asia: Geology, Exploration Technologies and Mines - Bali 2013 60 l The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration Zonation, Surface Geochemical Expression and Paragenesis. D. Menzies, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick, G. Morehari, B. Tekeve, B. Alupian, J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter, P. Golias The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration Zonation, Surface Geochemical Expression and Paragenesis D. Menzies1, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick, G. Morehari, B. Tekeve, B. Alupian, J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter and P. Golias Introduction The Miocene Wafi-Golpu gold-rich porphyry Cu-Au deposit, and associated epithermal Au mineralisation is located in the Morobe Province of PNG, and has a currently published resource of 28.5 million ounces of gold, 9.06 million tonnes of copper and 50.6 million ounces of silver (Newcrest, 2012; Harmony, 2012). The Wafi Au prospect was originally discovered in the late 1970’s with the Golpu porphyry Cu-Au mineralisation uncovered in the 1991, and later considerably upgraded in size during 2009 (Mueller et al., 2011). The Wafi-Golpu porphyry Cu-Au system is bounded by a NE to SW trending fault zone known as the Wafi Transfer, and intrudes a basement sequence of weakly metamorphosed well-bedded siltstones and conglomerates of the Oligocene Langimar Formation (previously interpreted to be the Owen Stanley Metamorphics). The Langimar Formation dipping between 50-80° to the E-NE has been intruded by several copper-gold mineralised hornblende phyric to feldspar phyric diorite porphyry bodies (Harris, 2010, 2011) and a late phase pheatomagmatic diatreme breccia. The diatreme breccia is 800 x 600m in diameter, bounded by pebble dykes, and is inferred to have vented due to the presence of accretionary lapilli in layered bands at surface. Mineralisation and Alteration Zonation Four discreet mineralising systems have been identified to date including: the Golpu porphyry Cu-Au system; the Nambonga porphyry Cu system; the Wafi Zones A and B high sulphidation epithermal Au mineralisation; and later Au-bearing Mn-carbonate veined and Au-rich, As-bearing pyrite epithermal mineralisation within Link Zone and Northern Gold Zone. The Golpu porphyry mineralised system exhibits a concentric alteration zonation consisting of a K-feldspar rich core (330 x 760m in diameter), grading out into a biotite–magnetic rich zone (650 x 1000m in diameter), an actinolite rich zone (640 x 1030m in diameter), grading out into a chlorite dominated zone. Strong sericite alteration overprint occurs at the eastern and western edges of the Golpu porphyry and also centrally within cross cutting fault/shear zones. The first appearance of actinolite alteration correlates with the first appearance of chalcopyrite and is coincident with the 0.1% Cu shell. A zone of intense silicification and quartz veining occurs on the upper northwestern margin of the Golpu porphyry mineralised system, where pyrite is dominant over chalcopyrite mineralisation. This zone also displays minor crenulated and layered quartz veining exhibiting unidirectional solidification texture as reported by Seedorff et al. (2005), who proposed this texture represents the transition between magmatic and hydrothermal conditions and demonstrates that fluids accumulated in the apex of a porphyry stock during crystallisation. The Golpu porphyry Cu-Au sulphide species have a concentric zonation from a bornite rich core grading out into chalcopyrite rich then pyrite rich zones. Au:Cu ratios are typically 0.6:0.9, and in several drill holes (WR416, WR426) Au has a positive correlation with observed bornite mineralisation (r=0.21, n=1890). This relationship is consistent with experimental work by Simon et al. (2000) who proposed bornite can accommodate one order of magnitude more gold than chalcopyrite. However, hand-specimen samples show evidence to suggest that Cu and Au may have been remobilised in zones of intense sericite alteration, where chalcopyrite is observed rimming bornite with appreciable Au grades, a relationship similar to that reported at Batu Hijau by Arif and Baker (2004). Molybdenite mineralisation is typically found on the margins and lower portions of the porphyry Cu-Au systems often associated with potassic alteration within quartzanhydrite veins, and occurs strongly in K-feldspar altered zones with later sercite overprint. Statistically analysis of drill core assays demonstrates a strong positive Pearson correlation between Cu and Au (r= 0.607, n=32653), a negative correlation between Mo and Au (r=-0.024, n=32653) and a neutral correlation between Cu and Mo (r=0.031, n=32653). Similarly the Golpu block model shows Cu+Au rich zones off-set from Mo-rich zones. On the south-eastern margin the Golpu porphyry A and B stockwork mineralisation is overprinted by a telescoped high sulphidation covellite-enargite-pyrite epithermal mineralisation and associated advanced argillic alteration. This high sulphidation epithermal Au-Cu mineralisation 1. Wafi-Golpu Services Ltd. Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 61 l The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration Zonation, Surface Geochemical Expression and Paragenesis. Plaate B. Plate A A. Plate C C. Plate EE. D. Menzies, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick, G. Morehari, B. Tekeve, B. Alupian, J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter, P. Golias Plaate D. Plaate A. Sttruccturral em mpla cem ment of o G Golpu and Nam mbo ongaa po orph hyryy inttrussion ns asso a ociatted with left‐ste eppiing sinistrral faul f t jogg, sho owin ng zon nation of f blue po otasssic (b biotite‐K‐feeldssparr‐ Maagnetitte) to greeen pro opy liticc altteraation (chlo orite‐acctinolitte+//‐ ep pidote) pro oducce b by hypeer‐saaline flu uidss ricch in n K, Na,, Fe chlorid des.. Plaate B. IIntrusio on o of th he d diattrem me d due to meteoric incu ursio on o on aa on oveerprint on porrphyyry due maagm maticc so ourcce. Sericitte aalteratio e to meteoricc draw w‐do own n. De epossitio on of chaalco opyrrite‐‐borrnite e miinerralissatio on by b a a lo ow den d sityy S‐rrich and Cu‐A C Au‐b bearringg ph hasee, and laaterr molyb bdenitee byy hyypersalline Fe, K and d Cll ricch brin b e as oxoch hloriide com mpleexess. Plaate C.. High H su ulph hidaatio n epittherrmaal vugg v gy siliica‐aalun nitee‐ pyyrop phyllite to dickitee‐kaaolinnite altteration n prroduceed by b an a early e y + volatile riich eveent rresu ultin ng frrom m the diisso ociattion n of H2S0 S 4 tto H H . A A latter liqu uid‐rich h evventt caarryying Au u‐Cu u‐Ass prroducin ng a a zo onaation n fro om enaargitte‐lu uzonitee, teenn antite‐tetrraheedriite tto ccove ellitee (ZZone e A, B, C C). Plaate D. Quaartz‐carrbonatee‐baase meetal + q quarrtz‐A As‐p pyrite‐rrich low w sulphiidattion epitheermal m mineerallisattion n pro odu uced d byy the e m mixin ng o of preegn nantt Au u‐Ass‐Pb b‐Zn n beearinng mag b rbon nate e m gmaatic fluiids with bicar surfacce w wateers ((Link Zo one, Noorth hern n Zo one and d up pperr Naamb bongga). Plaate E. P Postt minerral tthru ust ffaulltingg du uring th he P Plioccene (C Cloo os eet al., 20 010)) offf‐settin ng th he p porpphyry m mineeralisattion. FFigu ure 1. A parrageeneetic mo odeel fo or the t formaatio on of o tthe Wafi‐‐Go olpu u po orphyrry Cu‐A C Au min neraalissatio on, an nd h high h an nd low w ssulp phid dation Au minerralissation using fielld o obse ervaatio ons, workk byy (Errcegg ett al.., 1991 1) aand Rya an aand d Vigarr (19 999 9), pettrologyy b 9977) and draawing on mo odeels from SSilliitoe e (2 2010 0), Corbeett and a d Leeac h (199 98), Ulrich h and Maavro ogeeness by Zha Z ng et al. (19 (200 08) and d Li et al. (20012). East Asia: Geology, Exploration Technologies and Mines - Bali 2013 62 l The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration Zonation, Surface Geochemical Expression and Paragenesis. exhibits a zonation from a vuggy (or residual) quartzalunite bearing core, out to alunite-dickite, dickite-kaolinite with lesser pyrophyllite and diaspore, then illite-smectite alteration. Advanced argillic alteration dips to the east, subparallel to dominant bedding, is indicative of a lithological control to the alteration and mineralisation producing fluids (Erceg et al, 1991). This style of mineralisation exhibits sulphide species zonation from enargite-luzonite, to tennantite-tetrahedrite, covellite and As-bearing pyrite (Erceg et al, 1991). This high sulphidation mineralisation is cut by later Au-bearing Mn-carbonate bearing (Zhang et al., 1997) and As-bearing pyrite veins, interpreted to have affinities with Carbonate Base Metal Au mineralisation as defined by Corbett and Leach (1998). Zhang et al. (1997) interpret the occurrence of Au associated with Mn-carbonate (rhodochrosite) in the Link Zone core to be indicative of Au deposition associated with the mixing of bi-carbonate bearing meteoric waters with pregnant Aubearing magmatic fluids. Surface Geochemical Expression Surface geochemical data describes a broad annulus 2.94km x 2.7km which contains >140ppm Zn rimming the entire system, centred on the diatreme and is broadly coincident with the propylitic alteration zone. Zone A and B high sulphidation epithermal Au mineralisation occurs (manifests at surface) as a zone of anomalous Au values in soil samples (1.0 x 0.4km @ > 0.48 g/t Au). The southern portion of the Golpu porphyry Cu-Au mineralisation is identified at surface by spotty Cu (>150ppm) and Mo (>35ppm) anomalism in soil samples. The surface geochemical expression for both the Golpu and Nambonga porphyry Cu deposits is well defined using the multi-variant statistical analysis method, Principle Component Analysis (PCA). The PCA Cu-Mo and Au-Cu-Mo factors are the best indicator of both the Golpu and Nambonga porphyry Cu-Au mineralisation at depth. Paragenesis of Wafi-Golpu Mineralisation Wafi-Golpu porphyry Cu-Au and associated epithermal Au mineralisation are localised within a zone of extension associated with a left stepping sinistral fault jog, as part of the Wafi transfer structure as described by Corbett (1994). The porphyry mineralisation is interpreted to have been introduced by a two-phase fluid as proposed by Fournier (1999) comprising a hypersaline liquid rich in Fe, K and Cl and a low density S-rich and Cu-Au-bearing phase (Sillitoe 2010, Corbett and Leach, 1998). The negative correlation between Mo and Au-Cu is indicative of a separate transportation method for Mo into the system, possibly associated with the hypersaline Fe, K and Cl rich brine as oxochloride complexes as suggested by Ulrich and Mavrogenes (2008) and Li et al. (2012) or a separate intrusion phase of the complex. It is believed the diatreme intruded and vented due to a phreatomagmatic eruption resulting from the ingress of meteoric water onto a high D. Menzies, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick, G. Morehari, B. Tekeve, B. Alupian, J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter, P. Golias level intra/late mineral porphyry during rapid uplift (Corbett and Leach, 1998). Current drill hole WR457 shows a transition from hydrothermal breccia (diatreme) to a more magmatic-hydrothermal breccia with an apliticquartz-silica matrix, and eventually to a quartz lacking feldspar-biotite-hornblende phyric porphyry at depth below the diatreme. The lithologically controlled Zone A and B high sulphidation epithermal Au mineralisation then overprinted both the Golpu porphyry mineralisation and the diatreme, and were followed by later Au-bearing carbonatebase-metal and Au-As pyrite epithermal mineralisation commonly known as the Link Zone (Ryan and Vigar, 1999; Erceg, 2008). Recently observed cross-cutting relationships in Northern Gold Zone core (WR392) and petrological analysis of core from the Link Zone by Zhang et al (1997), as well as discussions by Ryan and Vigar (1999), indicate this is the latest mineralising event to have resulted from the mixing of pregnant metal bearing fluids with bi-carbonate bearing meteoric waters (Zhang et al., 1997; Corbett and Leach, 1998). Post-mineral thrust faulting is believed to be part of a Pliocene (5.0 - 2.5Ma) E-W compressional event (Reid, 2012, and Cloos et al., 2010)) and has offset the Golpu porphyry mineralisation to the NW. Figure 1 shows schematic diagrams of this paragenetic sequence. Copper mineralisation has undergone later supergene enrichment forming a chalcocite-rich zone with associated supergene kaolinite and alunite. References Arif, J. and Baker, T. 2004. Gold paragenesis and chemistry at Batu Hijau, Indonesia: implications for gold-rich porphyry copper deposits. Mineralium Deposita 39:523-535. Cloos, M., Sapiie, B., Quarles van Ufford, A., Weiland, R.J., Warren P. Q. and McMahon, T. P., 2010. Collisional delamination in New Guinea: The geotectonics of subducting slab breakoff. Geological Society of America Special Papers 2005;400;1-51 Corbett, G.J., 1994, Regional structural control of selected Cu/Au occurrences in Papua New Guinea, in Rogerson, R., ed., Proceedings of the Papua New Guinea Geology, Exploration and Mining Conference 1994: Melbourne, Australasian Institute of Mining and Metallurgy, p. 57−70. Corbett, G. J. and Leach, T. M. (1998) Southwest Pacific Rim Gold-Copper Systems: Structure, Alteration and Mineralization. Economic Geology Special Publication 6, 240p. Erceg, M. M., Craighead, G. A., Halfpenny, R., Lewis, P. J. 1991. The exploration history, geology and metallurgy of a high sulphidation epithermal gold deposit at Wafi River, Papua New Guinea. PNG Geology, Exploration and Mining Conference, 1991, p. 58 – 65. Erceg, M., 2008. Terry Leach: Contribution to the understanding of the hydrothermal ore-forming processes of the Wafi High Sulphidation Epithermal Gold Deposit and his role in the discovery of the Wafi Porphyry Copper Deposit. AIG Bulletin 48 – Terry Leach Symposium. Fournier, R.O., 1999, Hydrothermal processes related to movement of fluid from plastic into brittle rock in the magmatic-epithermal environment: ECONOMIC GEOLOGY, v. 94, p. 1193−1211. Harmony, 2012. Golu gold equivalent reserve ounces significantly enhances value of Harmony’s assest portfolio. (http://www.harmony. co.za/investors/news-and-events/company-announcements-2/ announcements-2012/641-golpu-gold-equivalent-reserve-ouncessignificantly-enhance-value-of-harmony-s-asset-portfolio) East Asia: Geology, Exploration Technologies and Mines - Bali 2013 63 l The Wafi-Golpu Porphyry Cu-Au Deposit: Mineralisation and Alteration Zonation, Surface Geochemical Expression and Paragenesis. Harris, A., 2010. Petrology Report; v.2: Summary of Petrological Observations from Drill holes WR315, WR316, WR318, WR320, WR321, WR323 (66 Samples). Internal unpublished report to MMJV. CODES ARC Centre of Excellent in Ore Deposits, University of Tasmania pp. 40 Harris, A., 2011. Petrology Report; v.3: Summary of Petrological Observations from Drill holes WR327A, WR328, WR331, WR331-W1, WR333 (36 Samples) - INTRUSIVE PHASES. Internal unpublished report to MMJV. CODES ARC Centre of Excellent in Ore Deposits, University of Tasmania pp. 26 Li, N., Chen, Y., Ulrich, T. and Lai Y. 2012. Fluid inclusion study of the Wunegetu Cu-Mo deposit, Inner Mongolia, China. Mineralium Deposita, 47:467-482. Muller, C., Bandy, L., Finn, D., Golias, P., Hayward, S., Menzies, D., Shakesby, S., Tekeve, B., and Wima, M. 2011. Unveiling a hidden giant: discovery of the Golpu Gold-Copper Porphyry Deposit, Papua New Guinea. NewgenGold Conference Perth, 2011. Newcrest, 2012. Golpu Pre-Feasibility Study and Reserve Announcement. (http://www.newcrest.com.au/media/resource_reserves/2012/ August_2012_Golpu_Pre-Feasibility_Study_and_Reserve_ Announcement.pdf ) Reid, R., 2012. Report on the Structure Modelling Completed on the WafiGolpu Project and Decline Route. MMJV Internal report. D. Menzies, S. Shakesby, J. Wass, D. Finn, N. Fitzpatrick, G. Morehari, B. Tekeve, B. Alupian, J. Kur, N. Kulinasi, G. Miam, J. Larsen, D. Peter, P. Golias Ryan, S. J. and Vigar, A. 1999. Discovery of the High-Grade Link Zone at Wafi, PNG. PACRIM 99 Congress, 10-13 October Bail Indonesia. The Australian Institute of Mining and Metallurgy Publication Series No 4/99. Seedorff, E., Dilles, J.H., Proffett, J.M., Jr., Einaudi, M.T., Zurcher, L., Stavast, W.J.A., Johnson, D.A., and Barton, M.D., 2005. Porphyry deposits: Characteristics and origin of hypogene features: ECONOMIC GEOLOGY 100TH ANNIVERSARY VOLUME, p. 251−298. Sillitoe, R. H., 2010. Porphyry Copper Systems. Economic Geology, 105:3-41. Simon, G., Kesler, S.E., Essene, E.J., and Chryssoulis, S.L., 2000, Gold in porphyry copper deposits: Experimental determination of the distribution of gold in the Cu-Fe-S system at 400° to 700°C: ECONOMIC GEOLOGY, v. 95, p. 259−270. Ulrich, T., and Mavrogenes, J., 2008, An experimental study of the solubility of molybdenum in H2O and KCl-H2O solutions from 500°C to 800°C, and 150 to 300 MPa: Geochimica et Cosmochimica Acta, v. 72, p. 2316−2330. Zhang, L., Leach, T., and Merchant, R., 1997. Petrographic investigations of drill core samples from holes WR158, WR159, and WR160, Wafi River Prospect, Papua New Guinea. Terry Leach and Co Unpublished report for CRA Exploration Pty Ltd. Report number 97128. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 64 l Case Study: Discovery and Geology of the Kham Thong Lai Copper-Gold Deposit, Lao PDR Paul Merriner Case Study: Discovery and Geology of the Kham Thong Lai Copper-Gold Deposit, Lao PDR Paul Merriner The Kham Thong Lai (KTL) deposit is a stratabound porphyry-skarn style copper gold system located approximately 8km ESE from the provincial town of Phonsavan in Xiengkhouang Province, Lao PDR (Fig. 1). It lies within the Mineral Exploration and Production Agreement granted to Phu Bia Mining. The deposit is situated proximal to the confluence area of the northern Loei Fold Belt (LFB) and Truongson Fold Belt (TFB) and lies within a complex and deformed arrangement of magmatic arc and rift volcano-sedimentary rocks and intrusives overlying Khorat type continental clastic sediments. Exploration work within the LFB and TFB has led to the discovery of several ore deposits including Phu Kham Cu-Au, Ban Houayxai Au-Ag, Sepon Cu-Au and Chatree Au-Ag. Orogenic activity associated with the development of the two belts has involved widespread plutonism and volcanic activity throughout the belt regions. It is this magmatism which has played a fundamental role in the formation of the KTL deposit. broad Au and Cu BLEG anomalies which ultimately led to the rediscovery of the KTL deposit. It was around this time that the name KTL was adopted by Normandy Anglo workers, which in Laotian translates as abundant gold and copper. Follow-up of this early work comprising geological mapping, gridded soil geochemical sampling and ground and airborne magnetics assisted in locating and defining KTL and directed Normandy Anglo to undertake a scout drilling campaign over the most prospective geochemical targets. This drilling consisted of 31 diamond drill holes, many of which returned significant gold and copper intercepts along Historically, copper at KTL was probably first identified by the local people of the area who referred to the site as Phu Thong, a name which is still in use today and literally translates as Copper Mountain in Laotian. Archaeological finds of bronze artefacts and the discovery of smelting furnaces in Laos confirm that metal production technologies were available and it may be that copper was mined and produced from KTL centuries ago, although this is unconfirmed. In more recent times during the French colonial administration small scale mining was undertaken at KTL from 1951 until 1953. In 1994 until 1996 Normandy Anglo Asian Pty Ltd, who were the original owners of Phu Bia Mining, undertook regional stream sediment sampling over the Phonsavan area. This work returned Figure 1. Location Map 1. Phu Bia Mining, Laos Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 65 l Case Study: Discovery and Geology of the Kham Thong Lai Copper-Gold Deposit, Lao PDR a 2.3 kilometre long E-W trending zone. At completion Normandy Anglo reported KTL as a significant resource of low-grade copper and gold and concluded that that the metal grades were not high enough to justify further work at that time. Exploration at KTL consequently ceased. In 2001 PanAust, then operating as Pan Australian Resources NL, took an 80% stake in the Phu Bia Contract Area in Laos. The remaining 20% of PBM was later acquired by PanAust from Newmont in 2005. Between 2004 and 2005 PanAust commenced a review of all previous work completed at KTL by its former owner. PanAust geologists also re-logged the Normandy Anglo drill core and remapped the prospect area. Based on this work PanAust recognised potential in the project and a decision was made to conduct further exploration work, which included gridded soil sampling, trenching and ground and airborne geophysics. Encouraging results consequently led to the resumption and continuation of exploration drilling from 2006 onwards. To date a total of 290 drillholes have been completed by PanAust, defining an indicated and inferred mineral resource (at 0.25% Cu cut-off ) of 89 MT @ 0.44% Cu, 0.18g/t Au and 1.7g/t Ag containing approximately 390,000 tonnes of copper, 515,100oz of gold and 4,864,400oz of silver. The majority of the stated mineral resource is primary mineralisation. The host sequence at KTL consists of an E-W trending, moderate south dipping, weak to moderately foliated sedimentary package of Late Carboniferous–EarlyPermian age which contains alternating sequences of strongly deformed interbedded siltstone, sandstone, micritic limestone and carbonaceous shales of passive shallow marine and volcaniclastic origin. The volcano-sedimentary sequence is intruded by rift related calc-alkali stocks that occur as elongated bodies and lobes showing a west to northwest trend. Late quartz-feldspar rhyodacite porphyry dykes intrude both the diorite and host sediments. At district scale the Phonsavan area lies at the margin of a south verging fold-thrust belt of probable late Permo-mid Triassic age. Evidence of the fold-thrust system is observed at KTL as localised brittle-ductile and ductile shear in the core. Statistical analysis of shear data indicates the shear fabric dips moderately south. Late WNW and NE structures also occur and appear to have formed after the timing of mineralisation. This faulting is responsible for disruption Paul Merriner and truncation of the deposit but not to a significant extent, based on recent modeling. Alteration styles within the host geology are complex and comprise diverse and localised alteration packages associated with different lithologies. Diorite and microdiorite intrusions exhibit propylitic (chlorite/carbonate/± epidote) alteration of varying intensity with strong development associated with stockwork zones and increasing in intensity toward skarn contacts. Weak to strong phyllic alteration is also widespread and occurs as sericite-silica-pyrite alteration within the diorite and sediments. Stockwork vein associated sulphide phases within intrusive bodies are also associated with weak to strong sericite-silica alteration. No significant potassic alteration is associated with the KTL deposit and only minor secondary biotite is observed in the core. Prograde altered calc-silicate skarns contain mainly garnet and pyroxene and typically show an outward progression from diorite to brownred garnet skarn to green-yellow garnet skarn to marble to limestone. Massive magnetite skarn occurs when the host rock has undergone complete replacement of the original mineral assemblage by magnetite. Base and precious metal mineralisation at KTL is considered to be coeval with stock emplacement. Re-Os age dating from vein hosted molybdenite returned an age of 289.4 ± 1.0 Ma. Mineralisation occurs as several styles. Low to moderate grade Cu-Mo-Au mineralisation is typically hosted in multi-phase stockworks and sheeted quartz-sulphide veins, and as disseminated and aggregate mineralisation within and proximal to intrusive stocks. High grade Cu-Au is associated with banded and semi-massive to massive sulphides hosted within prograde and more typically retrograde altered calc-silicate and magnetite-pyrrhotitepyrite exo-skarn. Skarn hosted mineralisation is more common and significantly higher in grade within exoskarn compared with endoskarn, the latter typically comprising mainly garnet skarn varieties. Dominant sulphide minerals for both styles are pyrite, chalcopyrite and pyrrhotite with less common molybdenite, bornite, sphalerite and galena. Secondary copper within the supergene profile is weakly developed throughout the deposit and occurs mostly in the form of malachite with lesser chalcocite and rare chrysocolla. The deposit is at the pre-feasibility evaluation stage with additional drilling to upgrade the resource base. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l keynote 66 The Magmatic Arc and the Slate Belt: Copper-gold and Tin tungsten and Gold Metallotects in Myanmar AHG Mitchell, Myint Thein Htay The Magmatic Arc and the Slate Belt: Copper-gold and Tin-tungsten and Gold Metallotects in Myanmar AHG Mitchell1 and Myint Thein Htay1 Myanmar can be divided into a Western province or arc system, comprising the Popa-Loimye magmatic arc and associated basins and ridges, and an Eastern province. The Eastern province consists, from west to east, of the Mogok Metamorphic belt; the Slate belt; the Paunglaung- Mawchi zone; and the Shan Plateau which was accreted to Asia in the Triassic. The Popa- Loimye magmatic arc and the Slate belt each host distinctive types of mineralisation and include, at Monywa and Mawchi, two of Myanmar’s four world- class mineral deposits (Fig.1). The Popa- Loimye magmatic arc is a discontinuous belt of intrusive and volcanic rocks extending from Mt Popa north and northeastwards through the extinct stratovolcanoes at Taungthonlon and Mt Loimye to near Bumba- bum south of Chaukan Pass. A forearc basin (Win Swe, 1972) and the Indo- Myanmar Ranges lie between the arc and GangesBrahmaputra delta in Bangladesh (Steckler et al., 2008) where the seismic Benioff zone dips very gently east. Three segments of the magmatic arc are separated by sedimentary cover. In the largest or Wuntho- Banmauk segment (United Nations, 1978) basement greenstone is overlain by a sequence of marine basalts and andesites, mudstones, dacites and mid- Cretaceous limestones. Calc- alkaline I- type plutons comprising the Kanzachaung batholith intrude the sequence below the limestones, and are mostly early Upper Cretaceous but locally Palaeogene. Mineralisation includes the Shangalon porphyry coppergold prospect in an Oligocene intrusive complex (United Nations, 1978), numerous mesothermal quartz - gold veins within the batholith and its host rocks, epithermal quartzgold veins, pyritic low-temperature replacement quartz bodies, and recently discovered occurrences of volcanogenic massive sulphide. To the south, in the Monywa- Salingyi arc segment, midCretaceous (95 to 105 Ma) I- type diorites and granodiorites intrude pillowed basalts and are overlain by late Tertiary sediments and in the north by small extinct basaltic stratovolcanoes (Chhibber, 1934a). At the Monywa copper mine ( Kyaw Win and Kirwin, 1998; Mitchell et al., 2011) sandstones, overlying stratified diatreme deposits, and midMiocene quartz andesite porphyry intrusions are cut by pebble dykes. Chalcocite-digenite and covellite occur with Figure 1. Map of Myanmar showing Popa- Loimye magmatic arc and Slate belt. Fa Falam, Ka Kalaw, Ky Kyaukse, Mc Mawchi, Me Mergui, Mk Mogok, Ml Meiktila, Mo Moulmein, Mt Myitkyina, Mu Mong Hsu, My Monywa, Na Namhkan, Ng Ngapali, Pd Padatgyaung, PMZ Paung Laung- Mawchi zone, Pu Putao, Sh Shinmataung, Ta Tavoy (Dawei), Tg Tagaung, Tk Tachilek, Ty Taunggyi. 1. Myanma Precious Resources Group, Yangon, Myanmar Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 67 l The Magmatic Arc and the Slate Belt: Copper-gold and Tin tungsten and Gold Metallotects in Myanmar pyrite in veins and pebble dykes, and as disseminations, in four high sulphidation epithermal deposits. Hydrothermal alteration assemblages which include quartz, sericite, pyrophyllite and alunite within more regional chlorite are overprinted by supergene kaolin. Barren leached caps up to 200 m thick overly the chalcocite and covellite which are partly hypogene but largely products of supergene enrichment. The pre- mining resource was over 2 billion tonnes containing 7 million tonnes copper. Nearby auriferous quartz veins occur in rhyolites and silicified sandstones. In the southernmost arc segment the Mt Popa stratovolcano overlies mid- Miocene and younger andesitic lavas which host widespread bodies of copper and gold- anomalous replacement quartz-pyrite-alunite within pyritic clays, and rare breccia dykes. Northeast of Taungthonlon, arc volcanics of Tertiary age underlie the Mt Loimye stratovolcano, and are reported at Kawt-a-bum and Bumba- bum (Chhibber, 1934a), the probable sources of alluvial gold in the Hukawng valley. The regional Sagaing dextral fault (Win Swe, 1972) offsets the arc’s speculative former continuation northeastward from Bumba- bum through the Tagaung-Myityina belt. The Slate belt in Myanmar (Fig.1) continues SSE for 2000km to Banka Island in Indonesia (Mitchell et al., 2012). It consists largely of Carboniferous to early Permian mudstones or argillites and quartzites, with thick diamictite beds implying glaciation in Gondwana. To the east the narrow Paunglaung- Mawchi zone of late Mesozoic sedimentary and volcanic rocks and older flysch may be an early Permian suture on which the Slate belt and western Myanmar collided with the Shan Plateau following eastward subduction of a Palaeotethys ocean. Within the Slate belt orogenic quartz- gold veins were discovered in 1999 by Ivanhoe Mines at Modi Taung northeast of Nay Pyi Daw. Gold here is in steeply- dipping narrow but high- grade stylo- laminated book- and -ribbon quartz veins within a 30 km long NNW-trending district. The veins, mostly tabular but with rare isoclinal folds, are hosted by argillites, intruded by calc- alkaline porphyritic dykes, extend for over 530 m vertically, and provide a resource grading over 30 g/ t Au. Gold values at Modi Taung exceed those of Ag, As, Cu, Pb and Zn, but veins 12 km to the north have higher base metal content. Since no veins occur in granites, we infer gold deposition from metamorphic fluids, perhaps during early Permian orogeny. AHG Mitchell, Myint Thein Htay Wolframite from several hundred tin and tungsten mines in the Slate belt accounted for 29 percent of global tungsten production in 1914. Deposits are associated with the apices of S-type, or reduced ilmenite series I- type peraluminous biotite- muscovite granites. Cassiterite is mined from alluvial deposits, pegmatites and quartz lodes, and wolframite from quartz lodes and bordering greisen (Chhibber, 1934b). Much production was from weathered material. Most of the wolframite is from the Mawchi mine, from Padatgyaung east of Nay Pyi Daw, and from the Tavoy (Dawei) region in southern Myanmar. Zircon U-Pb and the few Rb/Sr isotopic ages on the mineralised granites indicate late Cretaceous to Eocene ages (Cobbing et al.,1992, Mitchell et al., 2012), implying crustal melting younger than generation of the orogenic quartz- gold veins in the Slate belt. Many of the more productive tin- tungsten lode deposits are at high elevations, suggesting limited erosion and a stable landmass since the late Cretaceous. References Chhibber, H.L., 1934a. The Geology of Burma. Macmillan, London, 538p. Chhibber, H.L., 1934b. The Mineral Resources of Burma. Macmillan, London, 320 p. Cobbing, E.J., Pitfield, P.E.J., Darbyshire, D.P.F. and Mallick, D.I.J., 1992. The Granites of the South-East Asian Tin Belt. British Geological Survey, Overseas Memoir 10, H.M.S.O., London, 369p. Kyaw Win and Kirwin, D., 1998. Exploration, geology and mineralization of the Monywa copper deposits, central Myanmar. In Porphyry and Hydrothermal Copper and Gold Deposits: a Global Perspective. Proceedings of the Australian Foundation Conference, Perth, Australia, 61-74. Mitchell, A., Sun-Lin Chung, Thura Oo , Te-Hsien, and Chien-Hui Hung, 2012. Zircon U-Pb ages in Myanmar: Magmatic- metamorphic events and the closure of a neo-Tethys ocean. Journal of Asian Earth Sciences 56, 1-23. Mitchell, A.H.G., Win Myint, Kyi Lynn, Myint Thein Htay, Maw Oo and Thein Zaw, 2011. Geology of the high sulphidation copper deposits, Monywa mine, Myanmar. Resource Geology 61, 1-29. Steckler, M.S., Akhter, S.H. and Seeber, L., 2008. Collision of the GangesBrahmaputra Delta with the Burma arc: implications for earthquake hazard. Earth and Planetary Science Letters 273, 367-378. United Nations, 1978. Geology and Exploration Geochemistry of the Pinlebu-Banmauk area, Sagaing Division, northern Burma. Technical Report no. 2, Geological Survey and Exploration Project, United Nations Development Programme, DP/UN/ BUR-72-002, United Nations, New York, 69p. Win Swe, 1972. Strike-slip faulting in Central Belt of Burma. In: Haile, N.S. ( Ed.), Regional Conference on the Geology of Southeast Asia. Geological Society of Malaysia Newsletter 34, Annex, Abstracts, Kuala Lumpur, p.59. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 68 l Mineralisation Potential of the Kulu-Fulleborn Trend (Whiteman Range), New Britain Island, Papua New Guinea Chris J. Muller, Kieran Harrington, Hugh McCullough, Lindsay W. Bandy Mineralisation Potential of the Kulu-Fulleborn Trend (Whiteman Range), New Britain Island, Papua New Guinea Chris J. Muller1, Kieran Harrington1, Hugh McCullough1 and Lindsay W. Bandy1 Introduction Papua Mining plc controls exploration licences over an area of some 2,600 square kilometres along the Whiteman Range of New Britain Island, which stretches for 150 kilometres from Eleonora Bay on the north coast to the village of Fulleborn on the south coast. The geological setting is favourable for porphyry Cu-Au-Mo, high and lowsulphidation epithermal Au/Ag, high-grade skarn-type and volcanogenic massive sulphide mineralisation. Following the discovery of the Panguna deposit on Bougainville island in the mid-1960’s Conzinc Rio Tinto of Australia (CRA) commissioned a research vessel the CRAEStar to carry out a wide reaching survey of the Western Pacific Rim to explore for porphyry copper/gold deposits. The survey included reconnaissance geochemical surveys of New Britain Island and a series of stream geochemical anomalies were identified across the island including a number along the Whiteman Range. Since then sporadic follow-up exploration has been undertaken on New Britain by a number of companies. In 1968 Placer (PNG) Exploration Pty discovered a mineralised porphyry system at Plesyumi which it drilled in the early 1970’s. Subsequently, significant copper/gold/ molybdenum deposits were discovered at the Mt. Nakru and the Simuku areas. Most of the mineralisation discovered historically occurs within the Kulu-Fulleborn Trend, a corridor of Upper Oligocene-Pliocene intrusives and volcanics which follows the strike of the Whiteman Range (Fig 1.). The area has now emerged as one of the most prospective belts for Cu/Au mineralisation in Papua New Guinea. In recent years Australian junior Coppermoly Limited have reported a mineral resource at Simuku of 200 million tonnes at 0.36% copper, 61 ppm molybdenum, 0.06 g/t gold and 2 g/t silver. At the Nakru-1 deposit the same company has reported a resource of 38.4Mt at 0.82% copper equivalent. In July 2012 another junior explorer, Foyson Resources Figure 1. Map of New Britain Island, showing location of Papua Mining tenements with respect to deposits and prospects within the Kulu-Fulleborn Trend. 1. Papua Mining plc, Kula’s Place, Section 35 Alotment 13, Hibiscus Street (off Wards Road), Hohola, Port Moresby, National Capital District Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 69 l Mineralisation Potential of the Kulu-Fulleborn Trend (Whiteman Range), New Britain Island, Papua New Guinea Limited, reported that drilling by the company confirmed the presence of a significant mineralised porphyry system at Atui Prospect near Fulleborn. The exploration licence areas controlled by Papua Mining plc encompass approximately 70 percent of the KuluFulleborn Trend. Regional Geologic Setting The basement rock in the Kulu-Fulleborn Trend comprises Eocene – Oligocene Baining Volcanics, mainly consisting of andesitic lava flows and pyroclastic rocks interbedded with conglomerates and sandstones. The Kapuluk Volcanics (Oligocene – Miocene) are extensively exposed andesitic and dacitic lava flows and form the central Whiteman Range. The basement rocks were intruded by a series of gabbroic to dioritic stocks and plugs ranging in age from 29 – 22Ma (Page & Ryburn, 1977). The smaller dykes and plugs occur as elongate bodies aligned with regional NW and NE lineaments, suggesting a structural control during their emplacement. Simuku rocks possess arc tholeiite characteristics, while those from Plesyumi range from mafic, high-K gabbros to felsic, medium to low-K granodiorites (Horne, 2011). The Yalam Limestone was deposited around the flanks of the basement during a period of reduced volcanic activity in the Upper Miocence (22 – 10Ma) (Lindley, 1998). During a period of uplift and renewed volcanic/plutonic activity in the Pliocene period, the Mungu Volcanics and Kapiura Bed sedimentary sequences were laid down mainly to the north of the Whiteman Range. Volcanism continued intermittently from the Pliocene to present times. The Kimbe Volcanics (Pleistocene-Recent), consisting of ash and lapilli tuff, can blanket all lithologies including the basement rocks especially on the northern side of the Whiteman Range. In particular in lower areas several meters of cover could at times potentially mask the geochemical signature of mineralised bodies. Pre-Miocene structural deformation is dominated by almost orthogonal sets of NW to NE trending faults. The regional alignment of the basement and associated plutonic rocks closely relates to these prevailing trends, supporting structural control during igneous emplacement. PostMiocene deformation is dominated by NW-SE trending high angle horst and graben fault blocks. The Pre-Miocene faults seem to have been reactivated in most cases. Genetic Model for Intrusions and Associated Au/Cu Mineralisation Many Upper-Oligocene and Pliocene dioritic intrusives are localized in the Kulu-Fulleborn Trend and host porphyry copper, skarn and gold mineralisation (Titley, 1978). Significant zones of mineralisation include, from the northwest, Kavola East Prospect, Kulu-Simuku, Plesyumi Chris J. Muller, Kieran Harrington, Hugh McCullough, Lindsay W. Bandy and Mt. Nakru (Mackenzie, 1975; Hine and Mason, 1978; Titley, 1978). Local structural controls, superimposed on the prominent northwest trend, have clearly controlled Upper Oligocene emplacement. There is a general decrease in age of igneous activity in a northwest direction along the trend. This corresponds with a shallowing in the depth of formation of mineralization, from the deeper porphyry coppers at Kulu-Simuku and Plesyumi, to relatively shallow epithermal mineralization at Kavola East (Lindley, 2003). The two main recognised intrusive complexes at Simuku and Plesyumi are located approximately 70km from each other and are unlikely to have been separated by significantly greater distances in the past. However the complexes appear to be magmatically unrelated, being geochemically and isotopically distinct. The more felsic rocks of the Plesyumi Intrusive Complex possess geochemical characteristics that are typical of adakites. These differences may be explained through magma mixing, as opposed to fractional crystallisation (Horne, 2011). Slab melting formed adakitic melts and caused a pulse of melting in the aqueous fluidhybridized mantle wedge. K-rich magmas are commonly associated with Au deposits (e.g., Müller and Groves, 1993; Sillitoe, 2002; Blevin, 2002) and their presence as an end member in the Plesyumi mixing process raises the possibility that these magmas were the source of Au. Based on compilations of isotopic compositions for the western Pacific, the Oligocene to Miocene magmas of New Britain were derived from variable contributions of the mantle source of Pacific MORB (rather than Indian MORB) and ocean floor sediments comparable to Solomon Sea sediments. Exploration Strategy and Definition of Drill Targets From 2009-2010 Papua Mining plc completed a comprehensive historical technical data compilation exercise, collating all available geological, geochemical and remote sensing data. A study was completed on data from a 1982 Esso aeromagnetics and radiometrics survey which had covered the majority of the Kulu-Fulleborn Trend. Reduced to Pole (RTP) magnetic images highlight the KuluFulleborn Trend as several parallel structural linears and the known mineral occurrences are located on or proximal to these major lineaments. Most of the known porphyrystyle occurrences occur within well-defined magnetic low zones on the residual RTP magnetic image. Such zones may be related to hydrothermal activity associated with porphyry systems. These findings are significant in terms of exploration targeting, specifically for determining known mineralised trends from outside the concession area and, secondly, identifying new potentially mineralised areas. 3D inversion models were generated on subsets of the dataset for the known mineralised areas. The compiled exploration data was used to generate ranked prospective target lists and the company embarked on a East Asia: Geology, Exploration Technologies and Mines - Bali 2013 70 l Mineralisation Potential of the Kulu-Fulleborn Trend (Whiteman Range), New Britain Island, Papua New Guinea Chris J. Muller, Kieran Harrington, Hugh McCullough, Lindsay W. Bandy major field exploration program along the Whiteman Range during 2010, with teams carrying out rock chip and soil sampling, geological mapping and topographic surveys. a strongly positive correlation with the IP results, with a well-developed zone of high conductivity within the high chargeability zone. More than 40 km2 in the Nakru area was geologically mapped, by experienced geologists with a knowledge of the surface expressions of porphyry and porphyry-related systems. Lithology, alteration and structure were classified and mapped along all drainages and other exposures, with the aim of recognizing favourable host lithologies, hydrothermal alteration related to porphyry development and conducive plumbing and dilational environments, respectively. References To date more than 10,000 soil geochemical samples have been collected. Typically the soil grid spacing used is 400 x 50 metres. Substantial copper in soil anomalies (>100 ppm Cu in soils) were identified at Nakru (the Tripela and Flying Fox Anomalies), at Kori-Dagi five kilometres east of the known Simuku deposits, and at Plesyumi South in the vicinity of the known Plesyumi porphyry system. The mapping data revealed a range of porphyritic intrusives, amid intercalated volcanic tuff and pyroclastic packages, to some degree with breccia development along the contact zones. Zoned alteration is obvious in the Nakru area ( Junction anomaly), where a silica cap is surrounded by intermediate argillic alteration characterized by dickitekaolinite-pyrite. Distally, these alteration assemblages give way to sericite and finally chlorite dominated country rocks. Simultaneous rock chip sampling (for a total of more than 2,500 samples) was carried out with outcrop samples returning assays as high as 29% copper at Flying Fox and 25% copper at the Tripela prospect, both areas feature the occurrence of extensive diorite intrusives with associated hydrothermal, heterolithic, milled breccias. Several trenches have been excavated within the mineralised zones and results are pending. Induced Polarisation (IP) and Electromagnetics surveys (EM) have been completed at the Junction target. IP results there have outlined a resistive, low chargeability core, flanked by an annulus of high chargeability, typical of the response one might expect from a porphyry body. The EM data shows Several strands of the exploration work completed by the company to date therefore point to the presence of a number of porphyry systems within the exploration area. Drill testing of the most advanced target is scheduled to commence in March. The company anticipates an initial drilling programme at Junction of three or four diamond core drillholes to test the chargeability/conductivity target. Blevin, P. L. (2002). The petrogenic and compositional character of variably K enriched magmatic suites associated with Ordvician porphyry CuAu mineralisation in the Lachlan Fold Belt, Australia. Mineralium Deposita, 37, 87-99. Hine, R., Mason, D.R. (1978). Intrusive rocks associated with porphyry copper mineralisation, New Britain, Papua New Guinea. Economic Geology, 73, 749-760. Horne, P. (2011). The Plesyumi and Simuku Intrusive Complex, New Britain (PNG): Contrasting Magma Sources and Evolution in a Subduction Zone. MSc (unpublished). Lindley, I.D. (1998). Mount Sinivit gold deposits. In: Berkman, D.A. and Mackenzie, D.H. (Eds), Geology of the mineral deposits of Australia and Papua New Guinea. Australasian Institute of Mining. Lindley, I. D. (2003). Echinoids of the Kairuku Formation (Lower Pliocene), Yule Island, Papua New Guinea: Spatangoida. Proceedings of the Linnean Society of New South Wales. Mackenzie, D.H. (1975). Uasilau and Kulu porphyry copper occurrences, New Britain, in Economic Geology of Australia and Papua New Guinea, 1. Metals, edited by C.L. Knight (Australasian Institute of Mining and Metallurgy, Melbourne), Mono. 5, 845-850. Müller, D., Groves, D. I. (1997). Potassic Igneous Rocks and Associated Gold-Copper Mineralization. Lecture Notes in Earth Sciences, v. 56, (2nd, updated and enlarged ed.). Spring-Verlag, Berlin Heidelberg. Page, R. W., Ryburn, R. J. (1977). K-Ar ages and geological relations of the intrusive rocks in New Britain. Pacific Geology, 12, 99-105. Sillitoe, R. H. (2002). Some metallogenic features of gold and copper deposits related to alkaline rocks and consequences for exploration. Mineralium Deposita, 37, 4-13. Titley, S.R. (1978). Copper, molybdenum and gold contents of some porphyry copper systems of the southwestern and western Pacific. Economic Geology, 73, 977-981. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 71 l Alluvial and Bedrock Platinum, East Asia Yulia Nazimova, Gregory Ryan Alluvial and Bedrock Platinum, East Asia Yulia Nazimova1 and Gregory Ryan2 The most productive economic deposits of alluvial platinum in the world are associated with ultramafic zoned complexes of Ural-Alaskan (UA) type. While a number of deposits ranging up to 180 tonnes of metallic platinum have been mined very profitably in Russia, Canada, Alaska and Australia, only in the Russian Far East (Kondyor and Galmoenan) are such deposits still being mined. Alluvial and bedrock platinum deposits associated with the Galmoenan and Kondyor UA intrusions are the main topic under consideration. Bed-rock Platinum Deposits UA complexes are pipe-like, concentrically zoned, ultramafic-mafic intrusions of dunitepyroxenite-gabbro formation, typically ranging in size from 12 to 80 sq km. They occur in two distinct geological settings. The majority occur within mobile belts close to continental margins (eg Galmoenan). Such intrusions are more or less deformed, and may also be partially tectonically dismembered. More rarely, UA complexes intrude the stable continental platform. In this case, the zonal structure and the pipe-like shape Figure 1. Locations of the Galmoenan and Kondyor intrusions and their satellite images. are normally perfectly preserved (eg Kondyor). Both the Galmoenan and Kondyor intrusions exhibit a zonal structure with a well-developed dunite core (about 75-80% of the volume), surrounded by a clinopyroxenite rim 50-500m wide and some gabbroid occurrences. In the case of Kondyor, a later phase of alkaline rocks has developed, forming a network of veins in the dunite and clinopyroxenite. The Late Cretaceous Galmoenan intrusion is located in the north of the Kamchatka peninsula, Russia (Fig.1). The intrusion is elongate in a northeasterly direction, being 14 km long and 2–3 km wide. Based on gravimetric data, the intrusion represents a tectonic outlier, which is estimated to have been displaced some 8–15 km from the main thrust [1]. The Kondyor intrusion is located in the Russian Far East, about 1100 km north of the city Khabarovsk. Forming a circular, chimney-like structure about 8 km in diameter and at least 10 km deep (Fig.1), the massif has a dunite core 5.5 km in diameter. Age determinations are inconclusive, ranging from Mesozoic to Archean–Early Proterozoic (about 2.5 Ga) [4]. The main source of platinum is the dunite core, particularly the coarse-grained part containing chromite accumulations. Several mineralised zones have been delineated on both Galmoenan [7] and Kondyor [unpublished company reports]. These zones are characterised by centimeter to metre-scale chromite segregations occurring sporadically within the dunite. Platinum distribution within the chromite segregations is very irregular, with variations up to 340% having been encountered in individual samples. The “nugget effect” (isolated assays up to 100s of ppm Pt) is very characteristic of this style of mineralisation. 1. Director/Principal Consultant, NZ Exploration Ltd, 33 Richmond Road, Takaka 7183, New Zealand Corresponding author: [email protected] 2. Director/Principal Consultant, NZ Exploration Ltd, 33 Richmond Road, Takaka 7183, New Zealand Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 72 l Alluvial and Bedrock Platinum, East Asia At both Galmoenan and Kondyor, Fe-Cu-Pt alloys comprise more than 90% of PGM, with isoferroplatinum (Pt3Fe) strongly predominant. Numerous publications describe the PGE mineralogy of both complexes [3, 5, 7-9]. Detailed applied PGE mineralogy has been carried out on bulk samples from strongly mineralised zones of the Galmoenan intrusion [7, 9]. Similar work is currently being carried out on Kondyor. In samples with low and “background” Pt content, PGM (mainly isoferroplatinum) are finely disseminated, commonly in a cubic crystal form, whereas high-grade samples exhibit clustered aggregates (up to several centimetres) of Pt–Fe alloys, cementing the chromite grains. The average grain-size of the PGM in the mineralized zones is 175 µm. Despite the presence of large quantities of small inclusions of PGM (50%, <0.05 mm), the bulk (70%) of the actual metal content is composed of grains >0.4 mm [7, 9]. There is potential for economically mineable platinum deposits to exist within UA intrusions, particularly in Kondyor and Galmoenan. Such deposits are likely to comprise aggregates of many mineralised clusters, occurring with sufficient density and grade to be viable. Using appropriate exploration techniques in such settings would be critical to success. In particular, the trench and drill samples should be no less than 250 kg per 1m interval, in order to give reliable and repeatable results [7, 9]. It is also necessary to generate average grades over relatively large blocks. Pilot processing of bulk (several tonnes) samples should be part of this process. A very positive feature of such intrusions is that the platinum can be recovered by simple gravity separation [2]. While considerable bedrock exploration has been carried out in the past at Galmoenan, exploration is currently in progress only at Kondyor. Alluvial Platinum Deposits Since 1993, eight platinum placers have been delineated at Galmoenan. Of the seven currently being mined, the biggest, Ledyanoy and Levtyrinvayam, have produced about 25 tonnes of platinum each. The Ledyanoy placers formed in several creeks close to the intrusion, with productive horizons typically 2-3 km long, 20-130m wide and 0.45m thick, with average grade varying from 0.4-7 g/m3. Overburden thickness varies from a few metres to 60m. Interestingly, the Levtyrinvayam placer commences 10km from the intrusion. Various theories have been proposed to explain this but none has been substantiated. With a length of 9 km, width of 250-400m and thickness of 2.5-4m, the average grade of the productive horizon varies from 0.8-5.2 g/m3. Overburden thickness is typically 7-8m [1, 6]. The Kondyor placers occur both inside the ring structure (Kondyor River and its tributaries) and beyond the gorge through the ring, where the Kondyor flows into the Uorgalan River (Fig.1). Platinum placers are known to extend for 70 km downstream. Mining began in 1984 and annual production is still 3-4 tonnes. The average platinum Yulia Nazimova, Gregory Ryan grade varies from 0.5-5 g/m3 (up to 60-80 g/m3 in some parts) [3, 5]. At both Galmoenan and Kondyor, 70-95% of the platinum occurs in the basal wash, with minor quantities on “false bottoms”. Isoferroplatinum comprises 97% of the PGM, with grain size varying from 0.2-5mm close to the intrusion and from to 0.05-0.5mm more distant from the intrusion [1]. Grains also become more rounded with increasing distance from the intrusion. Typically 2.5% of the concentrates are composed of nuggets. Kondyor has produced more than 20 nuggets weighing more than 1 kg, the largest being 3.5kg [10]. The largest nugget from Galmoenan was 1.2 kg. Chromite and magnetite are also present in the concentrate and minor gold occurs at Kondyor. Alluvial platinum exploration employs similar techniques to those used for alluvial gold. Modern or fossil river channels must be delineated and then explored using bulk sampling methods, usually churn drill, cable tool rig or similar, or excavator, depending on depth to bedrock and ground conditions. Entire 1m samples are processed through a gravity separator such as goldsaver or small alluvial processing plant. The results are used to generate gradethickness contours and cross sections, to enable resource determination. Literature 1. Koryaksko–Kamchatsky region – a new platinum province of Russia.// Saint-Petersburg Cartographic Factory, VSEGEI Press, 283-315 (in Russian). 2. Bogdanovich A.V., Petrov S.V., Nazimova Yu.V., Vasilyev A.M., Urnysheva S.A. (2010): Peculiarities of processing minerals with high non-uniformity of valuable components distribution (example of platinum ores).// Obogashcheniye rud, 2, pp 3-8 (in Russian). 3. Mochalov, A.G. & Khoroshilova, T.S. (1998): The Kondyor alluvial placer of platinum metals.// Proc. Int. Platinum Symp. Theophrastus Press, Athens, Greece, pp 206-220. 4. Malitch K. N., Efimov A. A., Badanina I. Yu. (2012): The Age of Kondyor Massif Dunites (Aldan Province, Russia): First U–Pb Isotopic Data // Doklady Earth Sciences, Vol. 446, Part 1, pp. 1054–1058 5. Malitch, K.N. (1999): Platinum-Group Elements in Clinopyroxenite– Dunite Massifs of Eastern Siberia (Geochemistry, Mineralogy, and Genesis).// VSEGEI Press, St. Petersburg, Russia (in Russian). 6. Melkomukov V.N., Zaytsev V.P. (1999): Platinum placers of Seynav– Galmoenan knot (Koryak–Kamchatka province).// Platinum of Russia, III, pp 143-149 (in Russian). 7. Nazimova Yu.V., Zaytsev V.P., Petrov S.V. (2011): The Galmoenan massif, Kamchatka, Russia: geology, PGE mineralization, applied mineralogy and beneficiation// Canadian Mineralogist, v.49, 6, pp 1433-1453 8. Nekrasov I.YA., Lennikov A.M., Oktyabrsky R.A., Zalishchak B.L., Sapin B.I. (1994): Petrology and Platinum Mineralization of the Alkaline-Ultramafic Ring Complexes. Nauka, Moscow, Russia (in Russian). 9. Petrov S.V., Nazimova Yu.V., Bogdanovich A.V. (2010): Applied PGE mineralogy and ore beneficiation of the Galmoenan deposit, northern Kamchatka.// Proc. 11th Int. Platinum Symp. (Sudbury). 10. Sushkin L.B. (1996): Characteristic features of native metals from the Kondyor deposit.// Geology of Pacific Ocean, Vol. 12, pp 915–924. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 73 l The History of Coal Development in Indonesia A. H. (TONY) Osman The History of Coal Development in Indonesia A. H. (Tony) Osman The story of coal development and reconstruction in Indonesia over the past 150 years or so is one of the most remarkable that can be told today. Indonesia came from nowhere to its place in 2013 as the world’s largest exporter of thermal / energy coal. The narrative divides easily into several phases which are... 1. First beginnings to the Japanese occupation during the Pacific War 1942 2. Destruction and decline- 1942-1967 3. Reconstruction and the groundbreaking laws of 1/1967 (the foreign investment law) and 11/1967 (the general mining law) under the administration of President Soeharto. Emergence of Kalimantan as the location of export quality steam coal and discovery of high quality coking coal in Central Kalimantan. Sumatra with lower quality steam coal. 4. The concept of coal Cooperation Agreements, later to become Coal Contracts of Work. First, second and third generation, 1981 onwards. 5. Regional Autonomy legislation and the new mining law of 2009. The presentation outlines some of the present day challenges to coal investment by foreign investors especially the smaller companies. 1. PT Carsurin, Askrindo Building, Jln Angkasa, Block B-9, Kav.8 - Kemayoran, Jakarta 10601 Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 74 l Interpolating Assays and Physical Properties in Folded and Faulted Layered Geology Rod paterson Interpolating Assays and Physical Properties in Folded and Faulted Layered Geology Rod Paterson The GeoModeller Domain kriging algorithms, Guillen et al, 2011, implement two new methods for interpolating petrophysical properties (porosity, permeability, density, magnetic susceptibility) or chemical grades (Fe, Cu, Pb, Zn…) while honouring the geometry and internal structure of the host geological units. Traditional distance weighting interpolation methods that calculate the distance between samples using Cartesian coordinates (east, north and elevation) are not satisfactory in a folded and faulted stratigraphic unit or banded ore horizon. The distance between samples is no longer a straight line, Figure 1, Guillen et al, 2011. Current methods used to solve this problem involve unfolding prior to interpolation followed by reconstruction back to the original geometry. This can be a very difficult process in complex structural environments. Figure 1: Curvilinear distance between two points A and B: Point A is on the isovalue potA, point B is the isovalue potB. The distance dg (A, B) is the length of the arc AmBm (in blue) at isovalue potM = (potA + potB)/2. The distance dg (A, B) is therefore defined as dg (Am, Bm). The GeoModeller Domain Kriging algorithms are described below, Guillen et al, 2011. 1. When the variability of the parameter to study is mainly correlated with the pot coordinate (a metal deposited by a sedimentary process), the variogram in the space (pot, dg, q) is in reality a function of pot and we have: g(pot,dg,q) = g(pot) The normal coordinate to the isovalues, Figure 1, defines the potential coordinate (pot); it represents the value of the potential field function. Computation of potential distance (orthogonal to potential isovalues) between the two points A and B, pot (A, B) is very easy: it is the absolute value of the difference between pot (A) and pot (B). This can be thought of as a measure of formation thickness between points A and B. In this case, we have pure “zonal anisotropy” This algorithm is fast to compute due to its relative simplicity. 2. The General case: g(pot,dg,q) = g(pot,dgu,dgv) Where: • dgu,dgv represent respectively the geodesic distances along the u axis and the v axis, which are the axes representing the anisotropy in the xy plane. • dgu and dgv are the projection on the principal axes u and v of the geodesic distance dg and u and v are the directions of anisotropy on the plane xy rotated with an angle q from axis x and y. We may have a geometric anisotropy on the plane xy and zonal anisotropy along the pot coordinates and two pot different nugget effects for pot coordinate (C 0 ) and xy dg plane (C 0 ). Further work is required to improve the performance of this second domain Kriging algorithm in GeoModeller as it is computationally heavy. Data Import Storage, Validation and Kriging Procedures in GeoModeller GeoModeller allows the user to load 3D numeric drillhole data as from/to intervals attached to 3D drillhole desurveyed path objects where they can be viewed and compared with logged geology and the interpolated geology model computed by the dual co-kriging method, Lajaunie et al. 1997. A procedure to regularize (composite) irregular from/to sample intervals is available and should be used. Regularised drillhole numeric data is then transferred to a 3D vertex mesh for statistical/neighbourhood/variogram analysis and 1. B.Sc (Geology/Geophysics), FAusIMM, Intrepid Geophysics, Melbourne, Australia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 75 l Interpolating Assays and Physical Properties in Folded and Faulted Layered Geology interpolation. Alternatively 3D numeric point data derived from sources other than drillholes may be loaded directly into a GeoModeller 3D vertex mesh for analysis (surface and underground sampling, seismic velocity …). Geostatistical procedures follow the normal sequence of variogram analysis and cross validation followed by interpolation using the chosen Kriging method (1D, 2D, Domain Pot, Domain uvPot) or Sequential Gaussian simulation. An Inverse distance interpolator is also available. The Domain Kriging algorithms, by following the geology gradients, produce a tighter more natural distribution of interpolated physical values. Examples of the Application of Domain Kriging A folded and faulted resource example is presented to demonstrate the improvements that the new Domain kriging algorithms can make to more traditional classical Kriging interpolation results in this environment. The Domain Kriging method has also been used in the interpolation of physical properties (density and susceptibility) where the explorer wishes to determine whether his drilled resource target fully explains the observed geophysics (gravity and magnetic surveys). The interpolated physical property 3D grids or voxets are used as inputs to GeoModeller’s geophysical forward modeling and stochastic inversion. This is considered to be a more robust alternative to single property modeling of the resource geology. An ability to estimate geological uncertainty at all points in the 3D resource model is an extra independent capability of these techniques. Rod paterson Acknowledgements This work has been carried out on behalf of Intrepid Geophysics who is responsible for the commercialisation of GeoModeller through an agreement with BRGM, France. Many thanks to Antonio Guillen of the BRGM for his work in developing these new algorithms. References Guillen, A., Courrioux, G., Bourgine, B. (2011). 3D Kriging using potential fields surfaces, Proceedings IAMG 2011 conference September 5-9 2011, Salzburg, Austria Bertoncello, A., Caers, J.K., Biver, P., Caumon, G. (2008). Geostatistics on stratigraphic grids in Ortiz J et Emery X, Proc. 8th Geostatistics Congress, 2, 677-686 Calcagno, P., Chilès J.P., Courrioux G., Guillen A. (2008): Geological modelling from field data and geological knowledge: Part I. Modelling method coupling 3D potential-field interpolation and geological rules. Physics of the Earth and Planetary Interiors, Volume 171, Issues 1-4, December 2008, pp. 147-157 Chilès, J.P., Delfiner, P. (1999): Geostatistics: Modeling Spatial Uncertainty. John Wiley & Sons, New York, NY., 2nd Edition includes a proper introduction to the geology co-kriging estimation, at the core of Geomodeller technology. Jayr, S., Gringarten, E., Tertois, A.L., Mallet, J.L., Dulac, J.C. (2008): The need for a correct geological modelling support: the advent of the UVTtransform. First break 26. Lajaunie, C., Courrioux, G., Manuel, L. (1997): Foliation fields and 3D cartography in Geology 29, 571–584. Mallet, J.L. (2004). Space-time mathematical framework for sedimentary geology. Mathematical Geology 36, 1–32. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 76 l Porphyry Cu-Au Occurrences in Batulicin Area, Batangasai, Jambi Province, Indonesia Rusiana Permana, sufian nur hikmat, Yosafat P. Simanjuntak, Eratmadji, bronto sutopo Porphyry Cu-Au Occurrences in Batulicin Area, Batangasai, Jambi Province, Indonesia Rusiana Permana1, sufian nur hikmat1, Yosafat P. Simanjuntak1, Eratmadji1 and Bronto Sutopo1 Batulicin and Bujang prospect are located in Batang Asai district of Sarolangun region, Jambi province, Indonesia. The mineralization in Batulicin prospect is typified by CuAu comprising chalcopyrite in biotite-magnetite±Kspar alteration. Intermediate sulfidation epithermal overprint around Batulicin prospect produces quartz vein with galena, covellite, sphalerite and tennantite. Batulicin geology consists of volcanic and intrusive rocks. Volcanic andesite units, tuffs units (ash, accretionary lapilli, lapilli tuff-tuff breccia), crystal tuff, dacite porphyry, phreatomagmatic and phreatic breccia. There are three major intrusion consisting of diorite, porphyritic diorite and hornblend-quartz diorite (low altered-unaltered). The alteration is dominated by kaolinite. Weak sericitic-illite-kaolinite and illite-smectite appear in the west side of Batulicin, sericitic-illite±chlorite, chlorite-shreddy chlorite-sericitic±epidote, chlorite-biotitemagnetite±Kspar, sericite (muscovite-paragonite)illite-chlorite, advance argillic (pyrophyllite-alunitedickite-kaolinite±diaspore) and siliceous (massive-vuggy quartz) alteration appear in Batulicin upstream which forms Bujang lithocap. The porphyry veining is dominated by D vein, M vein, A vein, B vein, C vein also banded quartz vein which is overprints early vein. Meanwhile, the mineralization in Bujang prospect is typified by Cu-Au comprising covellite, chalcocite, and enargite in advanced argillic (pyrophyllite-alunite-dickitekaolinite±diaspore) and siliceous (vuggy-massive quartz) alteration. ASD Terra Spec™ used to delineate alteration zonation specially clay minerals (neutral to acid clays, low temperature to high temperature clays) as one of the vectors in fluid source interpretation. Bujang geology related to domediatreme complex which consist of coherent volcanic rocks (crystal tuff, volcanic andesite and dacite) also clastic rocks (phreatomagmatic breccia and hydrothermal breccia). The major mineralization in Bujang deep level of high sulfidation epithermal emerge in hydrothermal breccia and vein. The geophysics data like ground magnetic used to delineate high magnetic anomaly which is interpreted as biotite-magnetite alteration (prograde), low magnetic anomaly is interpreted as advance argillic and sericite alteration (retrograde). The resistivity used to delineate high resistivity anomaly which is interpreted as high silica alteration and the chargeability used to delineate high chargeability anomaly which is interpreted as pyrite shell. 1. PT. Aneka Tambang (Persero) Tbk. - Geomin Unit, Jl. Pemuda No.1, East Jakarta, Indonesia. Phone 021-4755380, Fax. 021-4759860 Corresponding author: [email protected], [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 Figure 1. Interpretative Geology-Alteration Map of Batulicin, Tangkui 77 l The Pani Gold Project: Geology and Mineralization C. Querubin, S. Walters, M. Papio, W. Satiyawan The Pani Gold Project: Geology and Mineralization C. Querubin, S. Walters, M. Papio, W. Satiyawan The Pani Gold Project is located in the central section of the north arm of Sulawesi, Indonesia, situated within the township of Hulawa, district of Buntulia, regency of Pohowatu, province of Gorontalo. The morphology within the area is typified by NE to NW trending ridges converging towards a central NW-SE oriented massif. Gunung Pani is viewed as a northeast trending ridge emanating from the central portion of this massif. Within the region, underlying Lower Miocene units are capped by sub-aerial rhyodacitic volcanics, which were later intruded by a Pliocene flow dome complex. Multi-phase emplacement of felsic magma in Pani is inferred to have been localized by Pliocene back-arc extensional rifting. The main lithologies within Pani comprise porphyritic to banded rhyodacites, lapilli tuffs, and fragmentals. Silicification is the type of alteration commonly observed and is exemplified by pervasive silica replacement of the rhyodacite groundmass. Pyroclastic units are generally argillized whereas heterolithologic volcanic breccias and porphyritic rhyodacites within the lower sections in the dome complex are mostly chloritized. Mineralization is strongly influenced by structural controls (i.e., extensional fractures) as well as by lithology (i.e., silicasericite altered porphyritic rhyodacites and pyroclastics, breccia fill, quartz-adularia-limonite veins, or disseminations in permeable volcanic lithologies and contacts). Concentric fractures rimming a 4 km wide diatreme towards the NW are assumed to represent sites most favourable for mineralization, especially at their intersections with district scale faults. 1. ??? 2. ???? Corresponding author: ??? East Asia: Geology, Exploration Technologies and Mines - Bali 2013 78 l Tectonics and Metallogeny of Mainland Southeast Asia – Framework for New Discovery Opportunities Neal Reynolds Tectonics and Metallogeny of Mainland Southeast Asia – Framework for New Discovery Opportunities Neal Reynolds The mineral industry of mainland Southeast Asia is underdeveloped and its mineral potential remains largely unrealised and generally not well understood. This reflects a range of factors from geological to historical and political. The present day operating and investment environment remains challenging in most jurisdictions; investment in exploration should minimise exploration risk through optimised understanding of metallogeny and discovery opportunities. From the Neoproterozoic into the Early Proterozoic, Southeast Asia was located on the northern Gondwana margin in the region of northern Australia. Mineral Southeast Asian metallogeny is intimately related to the long and complex history of accretion of Gondwanan terranes that formed the eastern part of the Asian continent. Due to substantial recent improvements in understanding, a metallogenic approach incorporating tectonic models and timespace reconstruction can provide a framework for regional- to belt-scale metallogenic targeting and a context for project assessment. Although significant uncertainties still exist, this understanding of metallogenic provinces can point to high priority areas with potential for new discoveries. The collage of cratonic and accretionary terranes that comprise Southeast Asia was derived from Gondwana in the Palaeozoic and amalgamated in the Mesozoic during Asian accretion. The Cathaysian terranes of South China and Indochina separated from Gondwana in the Early Palaeozoic, while the Sibumasu terranes separated in the early Permian. The Indochina and Sibumasu terranes are separated by accretionary arc belts developed on the active margin of Indochina from the Carboniferous to the Triassic. The Triassic to Jurassic Indosinian orogeny saw amalgamation of these terranes, together with North China and Tarim which accreted with Siberia across the Mongolian arc terranes forming the present day Asian continent. Post-Indosinian evolution of Southeast Asia reflects the development of fringing arcs, arc collision events, and the Cainozoic collision with India that had extensive far-field effects across the region. Figure 1: Summary terrane map of mainland Southeast Asia showing location of significant mineral deposits. 1. CSA Global, Perth, WA Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 79 l Tectonics and Metallogeny of Mainland Southeast Asia – Framework for New Discovery Opportunities Neal Reynolds systems in the Early Palaeozoic include Irish-type zinclead-silver and polymetallic VHMS in the Late Cambrian to Early Ordovician of the Sibumasu terrane, and Irishtype and SHMS zinc-lead in the Devonian of the South China terrane. SHMS zinc-lead mineral systems are also associated with rift and drift of Sibumasu from Gondwana in the Carboniferous. A-type in a continental arc setting and was associated with an evolving range of mineral systems including epithermal gold, intrusive-related gold, porphyry and skarn coppergold, carbonate-replacement zinc-lead-silver, sedimenthosted gold, and tin- and tungsten-polymetallic skarns and greisens. Indosinian orogenic gold is best seen in the Raub-Bentong zone of Malaysia. The culmination of the Indosinian orogeny in the Late Triassic saw development of the first phase of the Southeast Asian tin-tungsten belt related to late orogenic granites. Reactivation of old subduction zones in response to Indian collision saw development of Eocene to Miocene porphyry copper and epithermal mineral systems, especially in a belt from western Yunnan into Vietnam. The Late Carboniferous to Triassic saw development and accretion of arc and back-arc belts fringing the Indochina block. This is the most important metallogenic period in Southeast Asia with a range of mineral systems including VHMS, porphyry and skarn copper-gold, iron skarn, epithermal gold, and sediment-hosted gold. On the western Sibumasu margin, a second Late Cretaceous phase of tin-tungsten mineralisation in the southeast Asian tin-tungsten belt is associated with A-type magmatism in the Late Cretaceous. Porphyry copper-gold and epithermal systems developed in the central Myanmar arc belt in the Oligocene to Miocene with sediment-hosted gold systems in the back-arc in the Mio-Pliocene. Re-initiation of subduction outboard of the collision zones occurred along the western Sibumasu margin and eastern Indochina-South China margin in the Late Triassic to Jurassic. In South China and Indochina, JurassicCretaceous ‘Yanshanian’ magmatism evolved from I-type to The range of mineral systems in mainland Southeast Asia is broad and reflects the diverse and complex tectonic history of the region. The more-developed mining industry in contiguous belts in neighbouring southwest and south China provides a good indication of the remaining potential for discovery in Southeast Asia. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 80 l Age and O, Hf Isotope Systematics of the Yandera Porphyry Rocks - Constraints on Magma Sources, Crystallisation History and Crustal Evolution M. P. Roberts, R. A. Armstrong Age and O, Hf Isotope Systematics of the Yandera Porphyry Rocks - Constraints on Magma Sources, Crystallisation History and Crustal Evolution M. P. Roberts1 and R. A. Armstrong2 The Yandera Cu-Mo-(Au) porphyry deposit located on the northern flanks of Mount Wilhelm in the Papua New Guinean highlands is well-known (Figure 1). Exploration has been more or less on-going since ca 1965 and results covering such issues as structure and mineralisation have been published (Titley, 1978; Watmuff, 1978). Age dating using 1970s state-of-the-art Rb-Sr & Ar-Ar have also been of great help in unravelling the relationship between porphyry intrusions and country rock as well as the thermal effects on the latter (Page, 1976). In working with the Yandera porphyry rocks different companies have developed complex lithological classifications to deal with things such as bodies of breccia, rocks that look very similar to one another, contradictory cross-cutting relationships, textural variation and changes in mineralogy from the hydrothermal effects of overprinting mineralisation. Add to this the complexities from intrusion and crystallisation in an active structure, and the problems with lithological assignment are obvious. came from fresh core and surface exposures. It is worth pointing out that zircon chemistry is unaffected by surficial weathering processing and hence there is no prerequisite for fresh material although any contamination must be stringently avoided. Whole rock major and trace element analysis was also carried out on the fresh material as well as detailed petrology. The Yandera deposit is currently in advanced stages of exploration in the hands of Marengo Mining Limited with first production scheduled for 2016. The current resource comprises ca 5.2 billion Ibs Cu, 140 million Ibs Mo and 1.1 million oz Au. Chalcopyrite and bornite are the principal Cu-bearing species and molybdenite for Mo. The mineralisation occurs in well-defined structural domains along which the effects of alteration have been concentrated, and in certain areas within bodies of breccia. The importance In an effort to better define classification of the porphyry suite, an U-Pb zircon dating study using SHRIMP was undertaken. This was later extended to include Lu-Hf and O isotopes. The results of the dating and Hf-O isotope analysis and their petrogenetic and tectonic implications are presented here. It should be pointed out that this is work in progress and one of a plethora of different investigations currently underway. A suite of samples was collected covering the principal lithologies defined in the classifications under test. These samples Figure 1. Location of the Yandera deposit relative to other noteworthy deposits in Papua New Guinea. 1. Principal Geologist, Marengo Mining (Australia) Limited, 9 Havelock Street, West Perth, Australia Corresponding author: [email protected] 2 RSES, Australian National University, Canberra, Australia East Asia: Geology, Exploration Technologies and Mines - Bali 2013 81 l Age and O, Hf Isotope Systematics of the Yandera Porphyry Rocks - Constraints on Magma Sources, Crystallisation History and Crustal Evolution M. P. Roberts, R. A. Armstrong of ground preparation for mineralisation cannot be overemphasised and are part of ongoing research and modelling. The country rock for the Yandera deposit is the Bismarck Intrusive Complex, the most prominent member of which is a typical equigranular calc-alkaline I-type granodiorite with biotite and hornblende as its mafic minerals; some microgranular enclaves are present. An U-Pb zircon age of 10.42 Ma was obtained and no older inherited components were found in zircons from this rock. In contrast, U-Pb zircon ages from the Yandera porphyries are younger and define 3 groups spanning 7.1 to 6.3 Ma. The first group has ages between ca 7.1 to 6.9 Ma and are “equigranular” porphyries (plagioclase-phyric granodiorite) and one body of diorite, which may be an enclave from one of these contemporary granitoids. One sample hosts dessiminated chalcopyrite and may be evidence for an early stage of mineralising porphyry intrusion. The second group fall at ca 6.6 Ma and make up the bulk of the rock types sampled. These rocks cover a wide range of textural types from relatively equigranular porphyries (mistakenly assigned to the earlier phase in previous classification schemes) to quartz-phyric leucodacites. The former type have been found to underlay and form the matrix to some bodies of breccia. The youngest suite of dacitic porphyries have fragmental textures and date at ca 6.4 Ma. These rocks are cross-cut by mineralisation the age of which is unconstrained as yet. It is worth noting that no appreciably older inherited components apart from one Mesozoic age were found in zircons from these rocks. The major and trace element geochemistry of the porphyries show that these, like their country rock host, are typical calc-alkaline I-type granitoids. However, the younger group appear to have more tholeiitic chemistry. Overall, all of the porphyries are adakitic and there is a broad increase in Sr/Y ratio from oldest to youngest within the porphyry suite. The reason for this is unclear and may be due to any number of petrogenetic processes operating in the source region. The Lu-Hf and O isotopic analysis by SHRIMP, on the same spots in the zircons from which the ages were obtained, point to this source region as being juvenile, mantle-like in characteristic with a tight dispersion of eHf values and a looser mantle-like cluster for dO18. This feature of the O isotopes is most probably attributable to interaction with meteoric water in some cases and surficial weathering in others. Comparison of the Lu-Hf and O isotopes of the Yandera porphyries with those of the Ok Tedi Cu-Au deposit (Figure 2) (data from Van Dongen et al., 2010) show that the latter has a much greater crustal contribution and old inherited ages indicating that the source region for the Ok Tedi magmas was very different to that for the Yandera rocks. Crustal composition, thickness and depth to melting are important contributing factors to the metal budget observed at or near surface in porphyry systems. Van Wyck & Williams (2002) present U-Pb zircon data from the Omung metamorphics and Goroka formation Figure 2. InitialeHf vs d18O for the Yandera 1st and 2nd intrusive event rocks. Also included are the Hf and O isotopic compositions of zircons from Ok Tedi porphyries taken from Van Dongen et al. (2010) - data shown are those with intrusive ages and not Proterozoic inherited cores. also indicating Proterozoic contributions to rock formation. These authors suggest that the Markham Valley represents a major structural break separating older craton from newly accreted crust. The new data from the Yandera rocks dispute this and point to the break as lying to the south of the Bismarck range along the Bismarck fault. Timing of the Yandera magmatism appears to be at a similar age as the collision of the Ontong Java plateau with the Solomon Islands Arc postulated at ca 6 Ma (Petterson et al., 1997). This collision event could have caused the switch in motion sense of top to the SE to top to the NW along the Ramu-Markham and adjacent faults. A change in plate motion direction would cause the regional realignment of the stress field leading to rotation and dilation of preexisting structures, which are apparent from regional magnetic data over the Papua New Guinean highlands. These in turn could have formed the focus of magmatism and associated hydrothermal activity, and must have extended to lower crust - mantle depth to produce magmas of the type evidenced at the surface. Acknowledgements This abstract represents part of a technical paper in preparation. It forms one of a number of different research avenues currently underway and would not have got to this stage without input from the team of geologists currently or previously involved at Yandera - they are many. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 82 l Age and O, Hf Isotope Systematics of the Yandera Porphyry Rocks - Constraints on Magma Sources, Crystallisation History and Crustal Evolution References Page, RW, 1976. Geochronology of Igneous and Metamorphic Rocks in the New Guinea Highlands. Bureau of Mineral Resources, Geology and Geophysics. Report No: 162,117pp. Petterson, MG, Neal, CR, Mahoney, JJ, Kroenke, LW, Saunders, AD, Babbs, TL, Duncan, RA, Tolia, D and McGrail, B, 1997. Structure and deformation of north and central Malaita, Solomon Islands: tectonic implications for the Ontong Java Plateau-Solomon arc collision, and the fate of oceanic plateaus. Tectonophysics, Volume 283: pp. 1-33 Titley, SR, Fleming, AW, Neale, TI, 1978. Tectonic evolution of the porphyry copper system at Yandera, Papua New Guinea. Economic Geology, Volume 73: pp. 810-828. M. P. Roberts, R. A. Armstrong Van Dongen, M, Weinberg, RE, Tomkins, AG, Armstrong, RA, and Woodhead, JD, 2010. Recycling of Proterozoic crust in Pleistocene juvenile magmas and rapid formation of the Ok Tedi porphyry Cu-Au deposit, Papua New Guinea. Lithos, Volume 114: pp. 282-292. Van Wyck, N, and Williams, IS, 2002. Age and provenance of basement metasediments from the Kubor and Bena Bena blocks, central Highlands, Papua New Guinea: constraints on the tectonic evolution of the northern Australian cratonic margin. Australian Journal of Earth Science. Volume 49: pp. 565-577. Watmuff, G, 1978. Geology and alteration-mineralisation zoning in the central portion of the Yandera porphyry copper prospect, Papua New Guinea. Economic Geology, Volume 73: pp. 829-856. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 83 l Field Portable XRF – Good Techniques to Avoid Bad and Ugly Analyses. Stephen Sugden Field Portable XRF – Good Techniques to Avoid Bad and Ugly Analyses Stephen Sugden Field portable XRF (FP-XRF) instruments are a rapidly maturing technology which is revolutionising the exploration and exploitation of mineral deposits. The instruments offer a number of significant advantages to the geologist including: • Real-time, non destructive analysis in the field, reducing analysis turnaround times. • Integration of the instrument with GPS, mobile GIS devices and geochemical EDA packages such as ioGAS, enabling fast efficient interpretation of the analyses. • Results of interest and interpretations can be immediately acted upon, enabling program decision points to be brought forward. • Screening of samples to reduce analysis costs and prioritisation of shipment to remote laboratories. • The potential to undertake real time alteration and lithological mapping. To realise these benefits it is critical that users understand the limitations of FP-XRF instruments. These include: • Not all elements can be analysed, for example Na, while other light atomic mass elements such as Mg and Al may not be analysable on all instruments. • Analysis of some elements can be problematic due to spectral interferences. For example Fe with Co and Pb with As. • Limits of detection are often significantly higher compared to laboratory analyses. Depending on the instrument, detection limits for chalcophile elements such as Cu range between 5-30ppm, while lithophile elements such as K and Al range between 30ppm->1%. • The accuracy and precision of analyses are generally lower compared to laboratory analyses. It is rare that accurate readings are obtained without the application of calibration factors and reduced precision will be seen, depending on the degree of preparation undertaken. • Reductions in accuracy and precision are compounded by poor practises (e.g. short reading times and inadequate sample preparation). • Instruments have a number of modes of operation which are optimised for different suites of elements and concentration ranges (e.g. soil and mining) and some modes are not suitable for the analysis of geological samples (e.g. Alloy). The user therefore needs to select the mode/s most appropriate to their situation. Again reduced accuracy and precision will be seen if an inappropriate mode is used. A further consideration is compliance. The Table 1 checklist of the recently released 2012 JORC code now specifically mentions FP-XRF instruments, their calibration and reading parameters. Should analyses be released to the market then supporting discussion, detailing the underlying instrument set-up and analysis methodology will be required under the new “if not, why not” reporting requirements of the code. Many of these limitations however can be mitigated by completing a test and optimisation program to improve the accuracy and precision of the analyses and so demonstrate to the recipients of the analyses and regulatory bodies that they are “fit for purpose”. A typical test and optimisation program, used by ioGlobal, detailing issues to be considered is described below. 1. Selection and preparation of samples and/or standard reference materials for analysis. • Sample homogeneity. More homogenous samples will give more consistent results. The area measured by the instrument is around 1cm2 and the depth of penetration is generally limited to the surface for all except the lightest sample matrices. Biases therefore will result when analysing materials that are coarse grained and pulverising to produce a homogenous fine grained sample for analysis is almost always necessary. • Short cuts at this stage are the greatest source of error in FP-XRF analyses and ioGlobal considers good sample preparation to be a critical component in generating quality analyses and robust instrument calibrations. • Moisture content. Generally automatically corrected for by the instrument unless present in significant amounts. However moisture can cause dilution of 1. Principal Consultant, ioGlobal Pty Ltd, 369 Newcastle Street Northbridge, WA 6003 Australia. Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 84 l Field Portable XRF – Good Techniques to Avoid Bad and Ugly Analyses. results and impedes the ability to properly prepare samples. Laboratories always dry samples before analysis, so differences will be seen between field assays and check laboratory analyses when moisture is present. 2. Precision Assessment and Optimisation. • Instrument read time. XRF instruments measure the energy (KeV) and intensity (Counts/Second) of the secondary X-ray Fluorescence produced as a result of striking the sample with high energy X-rays. The energy emitted is characteristic for each element. As the intensity of the energy is measured in counts/ second, longer read times will generate a larger sampling set improving the ability to better resolve the energy spectrum produced, resulting in better precision and the ability (within limits) to analyse to lower concentrations. • Trials undertaken by ioGlobal have found that increasing read times often has the greatest impact in generating interpretable data. • Precision is assessed by analysing paired samples at different reading times and assessing the relative differences of the sample pairs. 3. Detection Limit Assessment. • The paired data is assessed using the detection limit calculation routine in ioGAS. • Ideally the majority of values for the elements of interest should be above the calculated detection limit and low enough that true background or grade cut off values can reliably be determined. • Should the detection limits not be suitable by either criterion, then reanalysis using longer reading times should be made. • It may not be possible to achieve suitable detection limits in which case the FP-XRF instrument analyses may not be “fit for purpose”. 4. Accuracy and Bias Assessment. • A selection of standards are analysed which: - cover the expected grade range, - have a similar sample matrix to the samples being routinely analysed, - are certified by a total analysis method for the elements of interest and - have concentrations for the elements of interest above the limits of detection limits previously determined. • Each standard should be analysed a number of times, using the reading time previously determined. The Stephen Sugden analyses are then compared to the certified value and ideally should be the same. • If there is an observed bias and the analyses have a suitable precision then a custom calibration factor may be calculated to improve accuracy. 5. Custom Calibration Factor Calculation. • Custom calibrations can be calculated by plotting either - a group of samples which have been analysed both by the FP-XRF instrument and a laboratory, using a total or near total analysis method, - or a set of standards which have been analysed using the FP-XRF. • The paired results are plotted on a scatter plot and a line of best fit calculated which is forced through the origin. The slope of the line (correction factor) is applied to the FP-XRF data to derive a corrected value. 6. Sample Packaging Signal Attenuation and Contamination Assessment. • Analysis of samples through plastic, fabric or paper bags, can impact on the accuracy of results and potentially introduce contaminants. Once the effect has been quantified then appropriate corrections can be applied to improve the ultimate accuracy of the analyses. • It has been noted (Innov-X 2010) that analysis through thin plastic bags can result in Cr, Ba and V values being lower by 20-30%. Test work by ioGlobal has also shown that for light atomic elements, analysing through plastic can degrade results by over 90%. Paper packets can also attenuate analyses and introduce contamination, for example Ti from paper whiteners. It has also been reported that some paper sample packets have high S contents. • To assess the effect of the packaging on accuracy, a series of samples are analysed in their packaging and by the laboratory. • Contaminant assessment is made by analysing a blank and noting if any contaminant elements are present. If the contaminant is an element of interest then a different packing material should be assessed to find a suitable replacement. References: Joint Ore Reserves Committee (2012). Australian Code for Reporting of Exploration Resullts, Mineral Resources and Ore Reserves. (The JORC Code 2012 Edition). Innov-X Systems (2010). User Manual, Delta Family: Hand Held XRF Analyisers. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 85 l A Lithocap in the Bujang Prospect, Jambi Province: Related or not Related to the Porphyry Cu – Au Mineralisation System Erric Sukmawan, Yosafat Palty Yudhistira Simanjuntak, Wanda Ilham Dani, Rusiana Permana, Bronto Sutopo A Lithocap in the Bujang Prospect, Jambi Province: Related or not Related to the Porphyry Cu – Au Mineralisation System Erric Sukmawan1, Yosafat Palty Yudhistira Simanjuntak1, Wanda Ilham Dani1, Rusiana Permana1 and Bronto Sutopo1 The Bujang prospect is an island arc setting located in the Southwest corner of Jambi Province in the Sunda Banda archipelago of Indonesia. The prospect is hosted in middle Tertiary volcanic and intrusive rocks within the Great Sumatran Fault Zone. Locally, sequence of andesitic dacitic volcanic and volcaniclastics breccias was cut by hydrothermal and phreatomagmatic breccias. Lithocaps exhibit heterogeneous distributions of mineral assemblages with each mineral showing a distinctive type of mineral deposition style. In Bujang Prospect, Jambi Province, the presence of massive-vuggy quartz indicates the development of epithermal - high sulphidation systems. This indication was followed by alteration mapping using short wavelength infrared (SWIR) reflectance spectroscopy methods that allows rapid identification of clay minerals which involves some key characteristics of these clays such as crystallinity and wavelength peak. This leads to a better understanding of the projects deposits systems, especially to interpret vector towards higher temperature zone of the systems and towards the proximal zone of the mineralisation. The host rocks are completely altered to advanced argillic and silicic alteration (lithocap) while low temperature, near neutral argillic is in the peripheral area. Lithocap in Bujang Prospect is dominated by acid alteration minerals formed in high temperatures such as alunite, pyrophyllite, kaolinite, dickite, diaspore. Four alteration zones lineated by these minerals, i.e., vuggy silica, advanced argillic, intermediate argillic dan sericitic zone hosted in andesitic to dacitic volcanic rocks and breccias. Hydrothermal breccia is one of the most intense mineralized host rocks that relate to high grade of Au, while phreatomagmatic breccia is related to high temperature pyrophyllite alteration that content juvenile-magmatic origin clast. Petrographic and mineragraphic studies of some selected mineralised host Figure 1. 1. PT. Aneka Tambang Tbk.- Unit Geomin, Jl. Pemuda No.1, Jakarta Timur Telp. 021-4755380, Fax. 021-4759860 Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 86 l A Lithocap in the Bujang Prospect, Jambi Province: Related or not Related to the Porphyry Cu – Au Mineralisation System rock shows the presence of enargite, pyrite and covellite associated with massive/vuggy silica. High grade Au is associated with partialy oxide rock that produces minerals such as jarosite, hematite and goethite. Advanced argillic zone associated with topaz showing the possibility of porphyry – related high sulphidation systems and then confirmed by the evaluation of several parameters, such as alunite wavelength peak and high magnetic anomaly in the center of Bujang Prospect. The identification of clay minerals in the surface by short wave length infra-red (SWIR) reflectance spectroscopy analysis shows alunite wavelength peak shifting from 1475 nm and reaching 1494.48 nm near JR 1 hill. Recent studies shows that the alunite wavelength peak shifts towards longer wavelength when it gets closer to the intrusive center (Arribas et al., 1995). Geophysics surveys in the Bujang lithocap shows Erric Sukmawan, Yosafat Palty Yudhistira Simanjuntak, Wanda Ilham Dani, Rusiana Permana, Bronto Sutopo several signatures where high resistivity is related to silicic alteration while low chargeability is barren, low sulfide content. First scout drilling in Bujang Prospect shows several mineral assemblages including pyrophyllite – paragonite, illite – smectite and kaolinite – smectite. These assemblages correlate with geophysics results, resistivity and chargeability, where each assemblages reflects certain colour in resistivity and chargeability sections. Two high magnetic anomalies (± 600 m width) that have a top of about 300 m below the surface were interpreted as intrusions that may host porphyry Cu systems in the center of Bujang diatreme complex. Further data and analysis from alteration mapping and test drilling will help with the understanding whether the high sulphidation systems in Bujang Prospect related to porphyry Au-Cu or not. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 l poster 87 Hydrothermal Alteration Study In Tertiary Volcanism Ayah Area, Southern Central Java Adi Sulaksono, Muhammad A. Luthan, Putu A. Andhira Hydrothermal Alteration Study in Tertiary Volcanism Ayah Area, Southern Central Java Adi Sulaksono1 ,†, Muhammad A. Luthan1, and Putu A. Andhira2 The Ayah Area is located in Kebumen Regency, Southern Central Java as a part of the Tertiary volcanism site in Sunda arc ( Java Island) Indonesia. Observations based on the aerial photographs show that more than 60% of the research area is volcanic terrain that controlled by geological structure indications with NW-SE relative trending. This situation becomes important because in many cases, hydrothermal alteration is mostly controlled by volcanic activity and geological structures. Many epithermal deposits are regionally associated with volcanic-related structures (Rytuba, 1981). Stratigraphically, the research area is composed by Late Oligocene – Early Miocene andesite intrusive unit as a feeder of paleovolcanism, Late Oligocene – Early Miocene volcanic breccia unit of Gabon Formation and disconformity Middle Miocene limestone unit of Kalipucang Formation (Asikin, 1994). Structural control of the research area such as NW-SE strike slip faults and joints (including sheeting joints in the intrusive rocks). In this condition, the role of joints is very important as the porous zone in hydrothermal system that cause strongly altered andesite. Some of faults are important as the pathways or porous zones for hydrothermal fluids that affect the pattern of alteration and alteration zoning. Several locations showed that along the river (fault zone) is the strongly altered rocks. The geological heritage of paleovolcanism is shown by the presence of volcanic activity products, include: intrusive rocks (andesite and basalt), vent breccia, andesitic lava, tuff breccia, lapilli tuff, laharic breccia, and pebbly sandstone. Referring to the volcanic depositional environment scheme by Bogie and Mackenzie (1998), Ayah area is the central to distal facies of a paleovolcanic system. This setting becomes interesting because the character of volcanic settings which host epithermal deposits is most commonly central to proximal, with volcanic- Figure 1. Surface alteration map (A) and cross-section (B) of the Ayah area, Kebumen Regency, southern Central Java. hosted deposits typically occurring with effusive or pyroclastic rocks (Sillitoe and Bonham, 1984). The end of Tertiary volcanic activity showed by Middle Miocene carbonate rocks of Kalipucang Formation. Because it was occurred after 1 Student of University of Pembangunan Nasional ”Veteran” Yogyakarta 2 Student of Padjajaran University † Author and presenter of poster East Asia: Geology, Exploration Technologies and Mines - Bali 2013 88 l Hydrothermal Alteration Study In Tertiary Volcanism Ayah Area, Southern Central Java the Tertiary volcanism activity, disconformity Kalipucang Formation is a barren zone. Evaluation based on hand specimen observations, petrographic analysis, and powder X-Ray diffraction analysis of some Gabon Formation’s altered rock samples show three hydrotermal alteration types (refer to Thomson and Thomson (1996)); chlorite - calcite ± epidote ± pyrite zone (propylitic type), quartz - montmorillonite ± sericite ± pyrite zone (argillic type), and kaolin - alunite - cristobalite zone (advanced argillic type). The outcrops of propylitic type is characterized by green to gray color. In the Ayah area, this altered rock zone has more extensive coverage than other types (> 60%). Based on field interpretation the propylitic zone is located on the outside of argillic zone. The argillic type is characterized by the presence of stockwork zones and quartz vein that show some Adi Sulaksono, Muhammad A. Luthan, Putu A. Andhira textures including: crustiform, banded, massive chalcedonic, vuggy quartz, sugary texture, and comb structure. Vein type mineralization associated with pervasive alteration of this type. In some locations, the pattern and distribution of this alteration zone is controlled by strike slip fault. The presence of advanced argillic alteration type is overprinting on the argillic zone. This alteration is characterized by the mineral assemblage: kaolin - alunite - cristobalite. The origin of alunite or this acid-sulfate alteration is formed by atmospheric oxidation of H2S in the vadose zone over the water table, associated with fumarolic discharge of vapor released by deeper boiling fluids (steam-heated) (refer to Bethke (1984) and Rye et al. (1992)). In the other hand, the presence of boulder vuggy silica at the surface of the research area confirms that there is an involvement of acidic hydrothermal condition that also forms advanced argillic type. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 89 l Cirianiu Epithermal Au, Vanua Levu, Fiji Geoff Taylor, Greg Corbett, Grace Cumming Cirianiu Epithermal Au, Vanua Levu, Fiji Geoff Taylor, Greg Corbett and Grace Cumming Introduction Detailed Geology Fiji is an isolated nation in the South Pacific Ocean approximately 3,000 kilometers north east of Australia. Vanua Levu is the second larger of the two major islands. North east Vanua Levu hosts a number of polymetallic and Au occurrences localized within a 15 km long graben formed by extension along the Nubu Fault, which is a major north east trending basement structure. The Cirianiu prospect which lies in the center of the graben comprises low sulphidation epithermal Au mineralization currently under investigation by Kalo Exploration. Previous explorers used vertical drilling to evaluate a model based upon flat lying replacement mineralization, whereas steep faults are now interpreted to have introduced mineralization which has been remobilized into a flat lying supergene blanket. The stratigraphy at Cirianiu has been divided into four recognizable units including: The Upper Sandstone Package, The Upper Qiriyaga, The Lower Qiriyaga and Lower Sandstone Package. Although most prominent in the Upper Quiriyaga Unit, allochthonous limestone blocks occur erratically throughout the sequence. The Upper Qiriyaga is dominated by lithic fiamme tuffs and breccias passing downwards to the Lower Qiriyaga boulder breccias and andesite fiamme breccia. A massive flat lying feldspar phyric andesite sill has gradational contacts into fractured andesite and in situ and clast rotated andesitic breccias. Hydrothermal Geological Setting The coalesced Mio-Pliocene volcanic fields which make up north eastern Vanua Levu are cut by the NE trending Nasavu and Nubu Faults formed as arc-parallel graben bounding faults. At Cirianiu NNE trending dilatant fractures have developed by a component of sinistral strike-slip movement during extension on the Nubu Fault. The volcanic vents erupted above and below sea level and were accompanied by the resedimentation of volcanic facies in a shallow marine environment. Large volume explosive eruptions are probably related to caldera collapse. A period quiescence followed evidenced by the deposition of fine grained sedimentary facies. Figure 1. Cross section 500N showing the development of high grade supergene Au overlying feeder structures. Note the exact dip on these structures remains unknown. 1. Geoff Taylor, Consultant, Savusavu, Fiji. Corresponding author: [email protected] 2. Greg Corbett, Consultant, Sydney, Australia 3. Grace Cumming, Consultant, Hobart, Australia East Asia: Geology, Exploration Technologies and Mines - Bali 2013 90 l Cirianiu Epithermal Au, Vanua Levu, Fiji breccias are fault related, steep dipping and flare upwards as funnels. The main hydrothermal breccia, the 17 breccia occurs on the F1 fault and parallel faults F1, F2, F3 and F4 all host supergene enriched high grade gold mineralization. Alteration Argillic alteration, illite-chlorite with variable silica pervasively floods the permeable volcanic and volcaniclastic rocks and commonly reduces the rock competency. Manganese is common and occurs as mounds and pervades the mudstones and fiamme tuffs and breccias. Silicification associated with argillic alteration floods along the flat bedded fracture planes and most importantly as intense silicification within the silica injection phase of the breccia pipes. The intense silicification makes the host rocks competent and amenable to cracking during Au mineralization. The silicified bedded sediments and coral clasts suggest this silicification has been formed by replacement of limestone and carbonate breccias. Inner propylitic alteration recognized as epidote veins and outer propylitic as chlorite-carbonate on the margins of the alteration system, are indicative of intrusion activity. Mineralisation Low grade Au mineralisation with hypogene grades of < 1.0 g/t Au occurs within pyritic illite altered breccias. It is mostly of the low sulphidation epithermal quartz - sulphide Au style. Gold is contained within the coarse cubic pyrite. The low grade ore is similar to Round Mountain (Nevada) style Au deposits and is amenable to heap leaching. Higher Au grades occur on faults at depth within more competent host rocks. Carbonate base metal Au mineralisation contains low temperature yellow sphalerite, galena and minor chalcopyrite which formed by the mixing of ore fluids with bicarbonate waters at low temperatures. Primary bonanza Au grades have not been recognized yet, but could develop in the cooler portions of the poorly eroded hydrothermal system. Geoff Taylor, Greg Corbett, Grace Cumming Supergene Gold Enrichment Significant supergene Au enrichment has concentrated collapsing down steep dipping faults and breccias to concentrate at the base of oxidation by both chemical and mechanical processes. The Ag: Au ratio is lower within supergene ores and displays a higher Au fineness than the hypogene mineralisation. Significant drill hole intersections in this zone of supergene enrichment include 86.0m @ 5.19g/t gold including 6.75m @ 37.8g/t gold and up to 2m @ 102g/t gold. The Model • Dilatant structures localize ore zones and are best recognized by northerly flexures within the major north east trending graben. • Parallel near vertical faults, F1, F2, F3 and F4 localize the ore bearing fluids and provide conduits for Au mineralization. • Both flat bedded silicification and fracture controlled silicification allow mineralizing fluids to crack the competent hosts and contain higher Au grades. • Significant supergene Au enrichment occurs at the base of oxidation and above the water table in these funnels. • The supergene high Au grade zones can contain exploitable heap leachable Au on the parallel structures and could represent a mineable gold resource. • Hypogene carbonate-base metal Au and quartz-sulphide Au mineralization has not been fully explored and low temperature sphalerite here indicates possible bonanza gold at higher levels of a poorly eroded hydrothermal system. • I.P. and resistivity surveys are likely to indicate coincident anomalies as drillable targets. East Asia: Geology, Exploration Technologies and Mines - Bali 2013 91 l Resource Estimation for the Aurukun Bauxite Deposit Andrew J. Vigar, Ian Taylor, Greg MacDonald Resource Estimation for the Aurukun Bauxite Deposit Andrew J Vigar, Ian Taylor, Greg MacDonald The resource estimation of lateritic deposits, such as Aurukun, presents specific issues related to the lateral changes in thickness and elevation of the various horizontal layers (or zones) within the deposit where the x and y dimensions are orders of magnitude greater than the z dimension. The objective was to develop a three dimensional (3D) block model that retained the vertical and lateral variation inherent in deposits of this type to allow full optimisation of the production plan without prior selection of an economic portion (enriched bauxite layers) of the profile at the resource estimation stage. The Aurukun bauxite deposit was held by Chalco Australia Pty Ltd (Chalco) until it withdrew from the agreement with the Queensland government in 2010 and it is now open for tender. The deposit forms part of the world class Weipa bauxite province, Cape York Peninsula, Queensland, Australia. The bauxite is predominantly pisolitic with an upper boehmite-rich zone and lower gibbsite-rich zone. The bauxite consists of both in-situ and reworked domains, is overlain by a thin soil horizon and has kaolinite clay as a transitional base. A Portable Infrared Mineral Analyser (PIMA) was utilised on site, in additional to elemental assay, on each drill sample to determine the mineralogy, in particular levels of boehmite, gibbsite, kaolinite and reactive silica. As part of the scope of work, a field program was undertaken using large diameter Boart Longyear Sonic drilling to acquire detailed density measurements across the deposit to allow compliance with Joint Ore Reserves Committee ( JORC) reporting requirements. Interpretation of the stratigraphy was conducted on a hole by hole basis with definition of the zone layering based on stratigraphy, geochemistry and mineralogy. The zone boundaries were then modelled as 3D surfaces and used to constrain a block model. The block model estimation used the Ordinary Kriging method, with the estimation done in unfolded space and then refolded, therefore maintaining the zones irrespective of thickness or orientation. The unfolding process converts the real-world positions for both blocks and informing samples to a scaled position relative to the roof and floor of each zone. Analysis of the data and variography were also undertaken in unfolded space. The x and y dimensions are unchanged, but the z dimension is a relative position. The effect of the unfolding and limits on number of samples per hole is to “push” the informing sample search sideways but within the stratification, rather than vertically. This honours the strong vertical zonation within the bauxite profile. The JORC code requires that the stated resource must have “reasonable prospects for economic extraction”. This is a qualitative rather than quantitative definition. A number of selection criteria to define a resource roof and floor were developed in consultation with the project engineers and owners to meet these criteria. The vertical selection of material to include in the resource highlights the variation in the development (and destruction) of the bauxite profile from area to area within the deposit. 1. ??? 2. ???? Corresponding author: ??? East Asia: Geology, Exploration Technologies and Mines - Bali 2013 92 l Developments in Microwave Digestion for Geochemical Analysis Brad Whisson Developments in Microwave Digestion for Geochemical Analysis Brad Whisson1 Digestion of mineral samples in acid has traditionally been regarded as a “low-tech” process, and there has been little development in this field over the past 30 years, prior to the advent of microwave digestion systems. The rapid energising of molecules and consequent acceleration of chemical reactions by absorption of microwave radiation has logically led to the use of microwave heating in chemical applications such as synthesis and digestion. Microwave-assisted digestion of mineral samples has been developed to a usable technique over the past decade, with several manufacturers continually refining their approaches and equipment. Samples are digested in sealed, PTFE-lined, microwavetransparent pressure vessels, and digest conditions are monitored via infra-red sensors and internal sensors. Digestions can be controlled with respect to microwave power, vessel temperature and pressure, which enables achievement of reproducible digestion conditions across a wide range of sample materials. Microwave-assisted digestion techniques have now been accepted by the scientific community in many areas, and are incorporated into various USEPA methods. A microwave-assisted digestion will typically reach completion in one tenth of the time taken by an equivalent hotplate method, which largely mitigates the capacity limitation of the equipment. The approach offers excellent recoveries for most mineral matrices when compared to other acid digest techniques. Microwave digestions are performed in sealed vessels at temperatures typically around 200°C and pressures of approximately 20 Bar, which has technical, environmental and operational benefits. As the oxidising power of acids generally increases with temperature, the oxidising effect of the acids is far greater in the microwave-assisted digestion than in atmospheric pressure digests. Microwave digestions are therefore very effective at decomposing sulphides, silicates and other resistant matrices. The use of sealed vessels in these digestions has the additional benefits of retaining volatile elements such as mercury and germanium in the digest vessel, and preventing cross-contamination from spitting. Although the technique is limited to sub-1 gram sample aliquots for practical purposes, modern sample preparation techniques reliably reduce particle size to the point where multielement analysis can be satisfactorily performed on a few tenths of a gram of sample. The sample size limitation precludes routine analysis for gold, due to sampling and detection limit constraints. LabWest adopted microwave assisted digestion as its primary decomposition technique from the start, developing methods that reliably catered for a wide range of geological materials, and has now analysed some 150,000 geochemical samples in its microwave systems. These have covered a wide range of sample types, and valuable insights to the strengths and potential of the technique have been gained. The analytical strengths of ICP-Optical Emission Spectrometry (ICP-OES) and ICP-Mass Spectrometry (ICP-MS) combined with microwave-assisted digestion enable determination of most metallic elements down to low detection limits. Aqua-regia-based, microwave assisted digests give consistently high recoveries for base metals, readily decomposing sulphides and most organic matter, and provide a cost-effective means of obtaining a wide range of information for the explorer. Hydrofluoric acid (HF) based digests are used where total decomposition of the host rock matrix is necessary, and good whole-rock approximations can be achieved with these digests. The ability of microwave-assisted digestion techniques to achieve high recoveries of the metals that are traditionally harder to extract by acid digestion (eg. Hf, Nb, W, Zr, RareEarths) lends itself nicely to litho-geochemical studies. A single digest solution can therefore be determined by combined ICP-OES and ICP-MS for suites of up to 63 elements, including base and trace metals, major rock-forming oxides and rare-earths. This has significant cost-saving implications, and enables exploration geologists and geochemists to gather a very detailed picture of the mineral environment in one step. Uranium exploration is particularly well catered for. Microwave digestion, when coupled with ICP-MS, offers very good recoveries of the rare-earths with typical detection 1. LabWest Minerals Analysis Pty Ltd, Perth, Western Australia Corresponding author: [email protected] East Asia: Geology, Exploration Technologies and Mines - Bali 2013 93 l Developments in Microwave Digestion for Geochemical Analysis limits of 0.05ppm or better. Parallel analysis of standard materials against the traditional techniques shows excellent recoveries for REEs and the more refractory elements. Microwave-assisted digestion offers a well-priced alternative to alkaline fusion or XRF for whole-rock analysis. Under microwave digestion conditions, appropriate acid mixtures containing HF completely dissolve most common rockforming minerals. The major oxide forming elements (Na, K, Ca, Mg, Fe, Al, S, P, Si) are determined from low levels (0.01%) up to high percentage levels in the rock. Brad Whisson Microwave digestion is also well suited to analysis of plant materials for trace elements. Plant materials are readily analysed for the full range of elements determined on mineral samples, including gold, and the very low detection limits required by geochemical exploration applications are achieved with ICP-Mass spectrometry. Future research and development directions will be discussed. East Asia: Geology, Exploration Technologies and Mines - Bali 2013