v. 76 - Geological Association of Canada

JANUARY
2003
Issue 76
Trace Element Geochemistry of Ultramafic Intrusions in the
Thompson Nickel Belt: Relative Roles of Contamination and
Metasomatism
Daniel Layton-Matthews1
O. Marcus Burnham
C. Michael Lesher
1
Mineral Exploration Research Centre
and Department of Earth Sciences
Laurentian University
933 Ramsey Lake Road
Sudbury, Ontario P3E 6B5
[email protected]
Introduction
Most magmatic Ni-Cu-(PGE) sulfide deposits are interpreted to
have formed from sulfide-undersaturated mafic or ultra-mafic
magmas by incorporation of crustal S and/or by the assimilation
of country rocks, resulting in sulfide saturation and the formation
of an immiscible sulfide liquid (Lesher et al., 1984; Naldrett,
1989; Naldrett, 1999; Keays, 1995). As a result of such processes
and the distinctive, yet compliment-ary, differences between the
trace element compositions of magmas derived by melting of a
depleted mantle source and those of typical continental crustal
rocks, the host rocks of many magmatic Ni-Cu-(PGE) sulfide deposits exhibit geochemical characteristics that are indicative of
magma-crust interaction (e.g. Lesher and Burnham, 1999; Lesher
et al., 2001). Although the recognition of crustal contamination
signatures within mafic and ultramafic rocks associated with
magmatic sulfide deposits may be of considerable value in mineral exploration, many magmatic sulfide deposits and their host
rocks have been metasomatized during regional metamorphism
leading to mobility of many of the elements that have been enriched or diluted during contamination. Below we summarize results of a
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Letter from the Editor
3
CIM Field Trips
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Las Médulas
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Vancouver 2003
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Calendar of Events
18
Fig. 1. Gravity (colour overlay) and shaded magnetic map of Manitoba. The TNB
forms the north-northeasterly trending leg of the Superior Boundary Zone (see inset). The gravity shaded magnetic map was created by the combination of 1) magnetic image represents the residual total magnetic field intensity, based on data from
the holdings of the National Aeromagnetic Data Base maintained by the Geological
Survey of Canada, and 2) a shaded relief image was created by using the HILLSHADE function in ARC/INFO's Grid module with an azimuth of 135º, an elevation of 45º, and a vertical exaggeration of 8. Yellow inset outlines study area.
(Continued on page 4)
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January 2003 – Gangue No. 76
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Editors Message
Dear MDD Members,
I would like to introduce myself, Kathleen (Kay) Thorne, as the new
editor for the GANGUE Newsletter. It is with great pleasure and honour
that I have accepted the editorial responsibility and feel that it is a wonderful opportunity for me to meet people in the geological community as
well as to keep on top of current and upcoming issues. Although I have
helped Dave over the past year with THE GANGUE, I realize that it isn’t
going to be an easy task as I have rather large shoes to fill since Dave and
Steve have done a wonderful job in the past! However, I’m sure with
Dave’s help behind the scenes pestering people for articles, the GANGUE
will continue to be a success. But I also need your help! You as MDD
Members are what keeps this newsletter going by submitting your contributions such as adverts, short articles, short course reviews, etc. so let’s
keep them coming in. Advertising in the GANGUE is free and keep in
mind that it is accessible to anyone on the web!
For those of you who aren’t aware of my background, I recently became employed with the New Brunswick Department of Natural
Resources and Energy as a Metallic Minerals Geologist. During my
undergraduate years, I worked with NBDNRE as a field assistant and
upon receiving my first degree from the University of New Brunswick, I
became employed as an exploration geologist searching for gold in southern New Brunswick. During a down turn in the industry, I decided to
pursue a Masters degree under the supervision of Prof. David Lentz
(whom all of you know very well I’m sure!) at UNB working on the Clarence Stream gold deposit in southwestern New Brunswick. The valuable
experience that I have gained through my studies has been phenomenal! I
have attended numerous conferences, went on many exciting field trips,
and met a tremendous number of people. These experiences have allowed me to establish some invaluable contacts, which would not have been
possible without the support of industry, academe and government.
Many of us tend to forget that experience is the backbone of our discipline. It is so important to keep this in mind when we see an opportunity
to allow a young, aspiring geologist to gain some invaluable experience.
It has gotten many of us to where we are today.
That is all for now! You will be hearing from me a great deal in the
future issues. Please bear with me for these first few issues while I grasp
to get a handle on things! If any of you can do anything to help in the
way of contributions or ideas, it would be greatly appreciated! Also if
you have any questions or comments, please feel free to drop me a line.
Best Regards,
Kay Thorne
GANGUE Editor
January 2003 – Gangue No. 76
3
two-year study on the effects of metasomatism on the ultramafic
intrusions in the Thompson Nickel Belt (TNB) and the implications of this study on geochemical exploration in metamorphosed
terrane.
Pearce element ratio (PER) plot (Fig. 2). The majority of collected samples plot on, or close to, an olivine control line with
only a few samples plotting toward orthopyroxene and clinopyroxene control lines. Samples plotting close to the orthopyroxene
line represent mesocumulate harzburgites with intercumulus orRegional Geological Setting
thopyroxene, whereas samples that plot on the orthopyroxene line
The Proterozoic TNB occurs along the western margin of the represent orthopyroxenite layers within ultramafic bodies.
Superior Province and is a remnant of an Early Proterozoic (1.9 – Primary Processes
1.8 Ga) collisional orogeny that involved the amalgamation of Least contaminated and relatively ‘unmetasomatized’ ultramafic
several micro-continental plates of a Proterozoic magmatic arc- rocks in the TNB are characterized by flat to slightly LREE
turbidite terrane belonging to the Trans-Hudson Orogen and
orthogneisses and derived migmatites belonging to the Superior
Province (Bleeker, 1990). The TNB comprises infolded Archaean
gneisses of the Pikwitonei Group, metavolcanic and metasedimentary lithologies of the Ospwagan Group, mafic/ultramafic
dykes, and ultramafic intrusions (Weber and Scoates, 1978;
Scoates and Macek, 1978). The TNB constitutes a large portion
of the Manitoba section of the Superior Boundary Zone (SBZ)
and is expressed as a ~500 km long positive Bouger gravity
anomaly trending ~030o that is easily recognized on a gravityshaded magnetic map of Manitoba (Fig. 1). The northern end of
the TNB is marked by a sudden change in the orientation of the
SBZ, where the SBZ assumes a near easterly orientation toward
the Fox River Belt. The Ni-Cu-(PGE) deposits in the TNB occur
within or near ultramafic bodies that occur within Ospwagan
Group metasediments, with the majority of the economic deposits
occuring in the northern portion of the TNB. Successive phases
of deformation during collisional orogenesis have resulted in
polyphase deformation and boudinage of what were presumably
laterally extensive ultramafic sills (Bleeker, 1990).
Geochemical Model
In other areas of the Superior Boundary Zone (e.g., Cape Smith
fold belt in northern Québec), the identification of magma-crust
interaction and consequent sulfide saturation in ultramafic intrusions can be used to discriminate between mineralized and nonmineralized intrusions (Lesher et al., 1999; Lesher et al., 2001).
In this case, the low metamorphic grade and relatively simple deformational history have allowed the preservation of primary
igneous geochemical compositions of the host mafic/ultramafic
rocks. However, all of the rocks in the TNB have undergone variable intensities of metasomatism and regional metamorphism,
which have modified their primary igneous geochemical compositions. Multiple episodes of deformation and metamorphic
grades that reach granulite facies, amongst the highest of any NiCu-(PGE) sulfide deposit, have complicated the understanding of
elemental mobility in the TNB. In the case of the TNB, the modified chemical compositions should contain information on both
metasomatized crustally-uncontaminated and metasomatized
crustally-contaminated intrusions.
Thompson Nickel Belt Ultramafic Intrusions
Samples taken from the TNB ultramafic intrusions for this study
include two lithologies based on modal variations in olivine,
chromite and interstitial minerals (chiefly pyroxene): 1)
metadunites and 2) metaperidotites. The dominance of olivine as
a cumulate phase is evident on a (Fe+Mg+Mn)/Ti vs. Si/Ti
January 2003 – Gangue No. 76
Fig. 2. Pearce Element Ratio plot of (Fe+Mg)/Ti vs. Si/Ti
showing the dominant control of olivine in the majority of the
samples taken from ultramafic bodies from the TNB.
depleted mantle-normalized profiles (McDonough and Sun,
1995) with [Ce/Sm]mn and [Th/Nb]mn ratios <1. Conversely,
crustally-influenced (contaminated) ultramafic rocks are characterized by LREE enriched mantle-normalized profiles with [Ce/
Sm]mn ratios 2-10 and [Th/Nb]mn ratios >1 (Fig. 3).
In thin section, these rocks look similar and are surprisingly
unaltered, containing relict igneous olivine (Fo90 average) and
enstatite (En86 average). Chromite occurs as euhedral to subhedral inclusions within olivine and intercumulus grains between
olivine.
Secondary Processes
With the exception of the cores of many of the ultramafic intrusions, almost all of the ultramafic rocks in the TNB have been
pervasively hydrated and K-metasomatized to serpentine ± magnetite ± brucite and serpentine ± talc ± magnesite ± calcite ± biotite assemblages. Although some ultramafic rocks such as kimberlites are enriched in alkalis, the major and trace element geochemistry of these rocks, especially the least-altered rocks, indicates that they are not derived from alkali-rich magmas.
Serpentinization
Alteration and metasomatism in the TNB ultramafic bodies occur
on two scales, regional and local. Regional alteration and metasomatism occurs throughout the TNB and is controlled by regional metamorphism and fluid access. Local alteration and metasomatism occurs along structural breaks and intrusion margins
and is specific to individual ultramafic intrusions.
Two broad styles of serpentinization can be distinguished on the
basis of texture in thin-section: 1) permeability-controlled serpentinization and 2) fracture-controlled serpentinization. Permeability-controlled serpentinization occurs in two textures: pseudomorphic and non-pseudomorphic. Pseudomorphic serpentinization is characterized by preservation of relict cumulate textures,
whereas non-pseudomorphic serpentinization is characterized by
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January 2003 – G angue N o. 76
5
Alkali-Carbonate Metasomatism
Fig. 3. Contrasting trace element patterns of typical leastaltered and uncontaminated ultramafic rocks (grey circles)
versus typical least-altered and contaminated ultramafic rocks
from the TNB. Primitive mantle normalization values from
(McDonough and Sun, 1995).
a loss of relict igneous textures. The transitional relationship from
partial serpentinization through pseudomorphic complete serpentinization to complete non-pseudomorphic serpentinization has
been observed in several ultramafic bodies, in which core fragments of unaltered olivine give way with increasing serpentinization to pseudomorphic and then non-pseudomorphic textures.
Pseudomorphic serpentinization textures in the TNB ultramafic bodies are characterized by the replacement of relict igneous
olivine such that, in plane-polarized light, the serpentine retains
ovoid olivine grain shapes. Serpentine mineralogy is dominantly
lizardite, which forms mesh and rare hourglass textures. This
mesh texture appears to be controlled by hydration along olivine
grain boundaries and by fractures within olivine grains.
Non-pseudomorphic textures are characterized by complete
recrystallization of serpentine. Pseudomorphic • -lizardite recrystallized to elongate interpenetrating needles and blades of antigorite. Recrystallization of lizardite to antigorite generally results in
recrystallization of magnetite into discrete grains and veinlets that
no longer define original mesh textures along olivine grain
boundaries.
Fracture-controlled serpentinization occurs as veins and
veinlets that crosscut all primary and hydrous mineralogy and
fabrics. In several unaltered to serpentinized ultramafic bodies in
the TNB, sets of oriented antigorite veinlets have been identified,
in which antigorite forms blades, branching blades, and massive
grains that clearly crosscut relict igneous minerals and early serpentine. In the late veinlet style of serpentinization, magnetite
occurs along vein margins.
January 2003 – Gangue No. 76
Many of the ultramafic bodies in the TNB contain alkali-rich hydrous and/or carbonate minerals, consistent with subsolidus interaction of the ultramafic rocks with a CO2-bearing hydrous, alkalic, LILE-enriched metamorphic fluid. From the overgrowth textures and chemistry of the alteration minerals, it is inferred that
this fluid infiltrated these bodies during the late stages of metamorphism and alteration. Potassic alteration in the komatiitic
rocks in the TNB, is generally accommodated by modal increases
in biotite, which may exhibit two distinct morphologies: 1) porphyroblastic growths and 2) mineral intergrowths.
In serpentinized rocks, porphyroblastic biotite (primarily
phlogopite) forms >2 mm-sized subhedral grains that appear to
crosscut existing serpentinization fabrics. Importantly, phlogopite
is absent in rocks that exhibit little or no serpentinization (i.e. exhibit relict igneous mineralogy), indicating that it is not a relict
igneous phase. In late porphyroblasts of antigorite, biotite often
forms intergrowth textures that appear to lie along the |001| cleavage plane of serpentine minerals. These intergrowths are thin,
generally less that 5 mm, and are difficult to identify by X-ray
diffraction techniques because of their small size. Such very finegrained intergrowths are also difficult to analyze using microanalytical techniques, which give analyses that are compositional
mixtures of serpentine and biotite.
Carbonate minerals are commonly present as an alteration
phase in komatiitic rocks, particularly ultramafic cumulate rocks
(Beswick, 1983). Carbonate alteration is present in many of the
ultramafic rocks in the TNB and, unlike potassic alteration, appears to be unrelated to the degree of serpentinization. The dominant carbonate alteration mineral in ultramafic bodies in the TNB
is magnesite, which forms the youngest alteration type identified
in the TNB. Late cream-colored magnesite veins crosscut all primary and secondary fabrics, including late chrysotile veins. In
unaltered to partially-altered ultramafic lithologies, magnesite
commonly forms anhedral grains that crosscut relict igneous olivine and secondary • -lizardite. Talc is commonly associated
with magnesite, forming a ‘feathery-textured’ core to many of the
anhedral magnesite grains.
The degrees of serpentinization and carbonation vary within
and between the ultramafic bodies in the TNB. In general, there is
a trend of increasing LOI with increasing MgO content, in agreement with modal observations of hydrous minerals in thin section. Many of the samples from ultramafic bodies in the TNB
have LOI contents that exceed the structural H2O capacity of serpentine (~16 wt%). This suggests that samples with • 16 wt%
LOI contain other volatile-rich minerals. An examination of the
relationship of LOI with CO2 indicates that the presence of magnesite, which contains 71% CO2, explains the high LOI in many
samples.
Mobility of major and minor elements is evident in examination of their variations with MgO content. TiO2, Al2O3, and FeO
correlate with MgO and form well-defined trends that are consistent with fractionation and accumulation of Ol ± Opx ± Cpx ±
Chr. However, SiO2, K2O, and Na2O all show considerable scatter around fractionation and accumulation trends. The addition of
Si and K is characteristic of potassic alteration and reflects modal
increases in biotite content. The apparent addition of Na, up to 1-
ultramafic rocks. The increase of Na with the degree serpentinization suggests that it occurred during hydration and the presence
of saline fluid inclusions in serpentinite bodies may be samples of
the hydrating fluid.
The addition of trace amounts of phlogopite in the ultramafic
bodies of the TNB can have pronounced affects on the K abundances. However, as documented by other workers (Beswick,
1983; Kerrich and Wyman, 1996; Lesher and Stone, 1996), the
addition of potassium is often accompanied by the addition of
other LILE. In the TNB ultramafic bodies, modal increases in
phlogopite result in proportional increases in Cs, Rb, and Ba,
whereas HFSE and REE appear to be much less affected.
There is a broad rough trend of increasing [La/Sm]mn ratio
with increasing LOI in the serpentinized ultramafic bodies in the
TNB. However, several of the REE patterns of nonpseudomorphic serpentinized ultramafic rocks from the central
TNB ultramafic rocks show anomalously high [La/Ce]mn ratios
relative to [Ce/Sm]mn, which are not consistent with igneous
crustal contamination processes and suggest preferential mobility
of La and/or preferential adsorption of La during metasomatism.
An examination of the relationship of [La/Ce]mn vs. LOI indicates
that all samples with anomalously high [La/Ce]mn have elevated
LOI. This, coupled with a near-zero correlation of [La/Ce]mn with
K or CO2 and a positive association of La enrichment with increased H2O, suggest that serpentinization rather than Kmetasomatism or carbonation was the mechanism for La addition
in these samples. In the absence of an identifiable La-rich mineral
phase in this study, the La enrichment is interpreted to represent
preferential La adsorption onto serpentine, which is supported by
experimental work (Tatsumi et al., 1986).
Geochemical Model - Revisited
The enrichment of La by metasomatic fluids may be distinguished from crustal contamination by comparing [La/Nb]mn and
[Nb/Ti]mn. Increases in [La/Nb]mn can be attributed to addition of
crustal material during magmatic assimilation (resulting in
stronger enrichment of La relative to Nb) or to addition of La
during metasomatism (resulting in the relative enrichment of La
and immobility of Nb). Because both Nb and Ti should be significantly less mobile than La in metasomatic fluids, but because
Nb is slightly enriched over Ti in most upper crustal rocks, asFigure 4. a) Plot of [La/Nb]mn vs. [Nb/Ti]mn for ultramafic
similation will increase [Ti/Nb]mn, but metasomatism will leave it
rocks from the William Lake area of the TNB. All values are
unchanged. Several ultramafic samples from the TNB exhibit an
significantly above detection limits. Mantle normalization
increase in [La/Nb]mn without a corresponding increase in [Nb/
values from McDonough and Sun (1995). See text for disTi]mn, indicating the addition of La without dilution of Nb (i.e.
cussion. b) Plot of [La/Th]mn vs. [La/Nb]mn for samples from
metasomatism).
the William Lake (grey circles) and Pipe (black circles) ulIf samples from the southern and northern TNB are comtramafic rocks. Pipe ultramafic samples exhibit a general
pared with respect to [La/Nb]mn and [La/Th]mn ratios, La addition
trend of increasing La/Nb with slightly increasing La/Th,
and crustal contamination with fractional crystallization (AFC)
suggesting La addition by contamination. However, samples
can clearly be distinguished (Fig. 5). Ultramafic rocks that have
from the William Lake ultramafic bodies exhibit increasing
constant [La/Th]mn ratios and increased [La/Nb]mn ratios are most
La/Th and La/Nb ratios, suggesting La addition during allikely the product of igneous contamination, whereas ultramafic
teration.
rocks with higher [La/Th]mn ratios are likely produced by La addition during alteration. It is therefore most likely that high
[La/Ce]mn ratios are a product of serpentinization and recrystalli2 wt% Na2O in some samples, is more problematic because no zation, whereas the enrichment of the remaining LREE is a prodmetasomatic phase that contains Na was identified in the TNB uct of primary magmatic contamination by crustal rocks.
January 2003 – Gangue No. 76
Conclusions
In order to study the effects of AFC processes, whole rock chemical data should be filtered for anomalous SiO2, K2O, Na2O, and
CaO concentrations, as they are mobile during alteration and metasomatism. Variation in these elements away from AFC trends,
for the most part, can be attributed to potassic and carbonate alteration, both of which can be readily identified in petrographic
analysis.
The effects of serpentinization on major and minor elements
appear to be minimal once the data are recalculated volatile-free.
La appears to have been mobile during recrystallization of serpentinite in ultramafic intrusions in the TNB. As such, [La/Sm]mn
ratios may be unreliable indicators of LREE-enrichment resulting
from crustal contamination during AFC of mafic and ultramafic
magmas. The absence of any correlation between [Ce/Sm]mn ratios and a number of indices of trace element enrichment suggests
that Ce may have been less affected by metasomatic alteration in
the TNB and that [Ce/Sm]mn ratios may be a more reliable indicator of magmatic assimilation processes. For example, in comparing [Th/Nb]mn vs. [Ce/Sm]mn variations in the northern TNB with
those in the central and southern TNB (Fig. 5), the effects of metasomatism can be minimized and primary processes become apparent. The high [Th/Nb]mn and [Ce/Sm]mn ratios of the northern
TNB relative to the lower [Th/Nb]mn and [Ce/Sm]mn ratios in the
7th BIENNIAL SGA MEETING
Athens, Greece
24-28 August 2003
The 7th Biennial SGA Meeting "Mineral Exploration and Sustainable Development" will be held in Athens, Greece (August 24-28,
2003). Athens is the historical capital of Greece, a scientific and cultural center and the Host City of the Summer Olympic Games of
2004.
The meeting will be organized by the Society for Geology Applied
to Mineral Deposits (SGA) in cooperation with the Institute of Geology and Mineral Exploration, Athens Technical University, University of Thessaloniky and Geological Society of Greece (Section
of Economic Geology and Geochemistry).
Under the general theme "Mineral Exploration and Sustainable
Development" the organizers would like to bring together economic geology scholars and professional exploration and mining geologists to discuss current issues on ore geology, exploration and sustainable development. Participants are kindly invited to
offer papers for oral and poster presentations. There is an opportunity to have meetings and sessions of ongoing and planned Projects and Working Groups. Proposals for conveners and topics
of sessions are welcome.
Several pre- and post-meeting field trips will be organized and the participants will have the opportunity to visit different metallogenic provinces of Greece and neighboring countries.
The first circular will be available at the following address: www.igme.gr/sgaconference.html
Contact address
7th SGA Biennial Meeting
Secretary: Dr. Demetrios Eliopoulos
Institute of Geology and Mineral Exploration
70 Messoghion Str.
GR-115 27 Athens, Greece
Fax: 0030 - 1 77 73 421
e-mail: [email protected]
January 2003 – Gangue No. 76
central and southern TNB is consistent with the high proportion Manitoba Geological Survey, INCO Ltd., and Falconbridge Ltd.
of economic deposits in the northern TNB.
for their cooperation and logistical support during this study.
ACKNOWLEDGEMENT
REFERENCES
Support for this study was received from the Canadian Mining Beswick, A.E., 1983. Primary fractionation and secondary alteration within an Archean ultramafic lava flow. Contributions
to Mineralogy and Petrology, v. 82, p. 221-231.
Bleeker, W., 1990. Evolution of the Thompson nickel belt and its
nickel deposits, Manitoba, Canada. Unpublished Ph.D. thesis, University of New Brunswick, Fredericton, NB, 400 p.
Gromet, L.P., Dymek, R.F., Haskin, L.A., & Korotev, R.L., 1984.
The "North American shale composite": its compilation, major and trace element characteristics. Geochimica et Cosmochimica Acta, v. 48, p. 2469-2482.
Keays, R.R., 1995. The role of komatiitic and picritic magmatism and S-saturation in the formation of ore deposits.
Lithos, v. 34, p. 1-18.
Kerrich, R. & Wyman, D.A., 1996. The trace element systematics of igneous rocks in mineral exploration; an overview, in
Wyman, D. A., ed., Trace element geochemistry of volcanic
rocks; applications for massive sulphide exploration, Geological Association of Canada, Short Course Notes 12, p. 150.
Lesher, C.M., Arndt, N.T., & Groves, D. I., 1984. Genesis of
komatiite-associated nickel sulphide deposits at Kambalda,
Western Australia; a distal volcanic model, in Buchanan, D.
L. & Jones, M. J., eds., Sulphide deposits in mafic and ultramafic rocks.: London, United Kingdom, Institute of Mining & Metallurgy, p. 70-80.
Lesher, C.M. & Burnham, O.M., 1999. Mass balance and mixing
in magmatic sulphide systems, in Keays, R., R., Lesher, C.
M., Lightfoot, P.C., & Farrow, C.E.G., eds., Dynamic processes in magmatic ore deposits and their application to mineral exploration, Geological Association of Canada, Short
Course Notes 13, p. 413-449.
Lesher, C.M., Burnham, O.M., Keays, R.R., Barnes, S. J., &
Hulbert, L., 1999. Geochemical discrimination of barren and
mineralized komatiites in dynamic ore-forming magmatic
systems, in Keays, R.R., Lesher, C.M., Lightfoot, P.C., &
Farrow, C.E.G, eds., Dynamic processes in magmatic ore
deposits and their application to mineral exploration, Geological Association of Canada, Short Course Notes 13, p.
451-477.
Lesher, C.M., Burnham, O.M., Keays, R.R., Barnes, S.J., & Hulbert, L., 2001. Trace-element geochemistry and petrogenesis
of barren and ore-associated komatiites, in Barnes, S. -J.,
Fig. 5. Ce/Sm vs Th/Nb mantle normalized plot for the NorthCrocket, J.H., & Martin, R.F., eds., Ore-forming processes in
ern TNB (A) and central/southern TNB (B). Low Th/Nb and
dynamic magmatic systems. Canadian Mineralogist, v. 39, p.
Ce/Sm ratios should correlate with a low degree of ultrama673-696.
fic/contaminant interaction, whereas a high Th/Nb and Ce/Sm
Lesher,
C.M. & Stone, W.E., 1996. Exploration geochemistry of
ratios should correlate with a high degree of ultramakomatiites,
in Wyman, D. A., ed., Trace element geochemisfic/contaminant interaction. MORB (Sun and McDonough,
try
of
volcanic
rocks; applications for massive sulphide ex1989) and NASC - North American Shale Composite (Gromet
ploration,
Geological
Association of Canada, Short Course
et al., 1984).
Notes 12, p. 153-204.
McDonough, W.F. & Sun, S.S., 1995. The composition of the
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gineering Research Council of Canada. The authors thank the Naldrett, A.J., 1989. Magmatic sulfide deposits. Oxford, United
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Kingdom, Oxford University Press, 186 p.
and Geothermal Research, v. 29, p. 293-309.
Naldrett, A.J., 1999. World-class Ni-Cu-PGE deposits; key fac- Weber, W. & Scoates, R. F. J., 1978. Archean and Proterozoic
tors in their genesis. Mineralium Deposita, v. 34, p. 227metamorphism in the northwestern Superior Province and
240.
along the Churchill-Superior boundary, Manitoba, in Fraser,
Scoates, R.F.J. & Macek, J.J., 1978. Molson dyke swarm. ManiJ. A., and Heywood, W. W., eds., Metamorphism in the Catoba Department of Energy and Mines, Mineral Resources
nadian Shield. Geological Survey of Canada Paper 78-10, p.
Division, 53 p.
5-16.
Sun, S.-S. & McDonough, W. F., 1989. Chemical and isotopic
systematics of oceanic basalts: implications for mantle com- Editors’ Note: This was one of three Boldy Award presentations
position and processes, in Saunders, A.D. & Norry, M.J., at the Saskatoon 2002 GAC-MAC annual meeting.
eds., Magmatism in the Ocean Basins. Geological Society of
London Special Publications 42, p. 313-345.
Tatsumi, Y., Hamilton, D. L., & Nesbitt, R. W., 1986. Chemical
characteristics of fluid phase released from a subducted lithosphere and origin of arc magmas: evidence from high pressure experiments and natural rocks. Journal of Volcanology
May 4 to 7, 2003
For more info, visit www.cim.org
Conference themes
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Premeeting
Workshops
Postmeeting
Field Trips
1. Valuation of Mineral Properties
2. Covers for Reactive Tailings and Waste Rocks: Recent
Developments and Applications
3. Practical Exploration Geochemistry
4. Applied Mineralogy Related to Exploration and
Exploitation of Ore Deposits.
5. Workshop on Environmental Management System
(ISO 14001) implementation
6. Asset Reliability
7. Knowledge Management
8. "The Lubrication Aspect of Machinery Health
Management"
9. A How-To Guide in Mine Ventilation
10. System Thinking for Quality Management and Continuous Improvement
11. Integrated Methods in Mineral Exploration; Applications
in the Use of Remote Sensing
12. Blasting Technology
13. Workshop on Diamond Exploration
Trip No. 1 - From a Monteregian Hill to the
Appalachian Mountains; 400 Million Years of Earth History
January 2003 – Gangue No. 76
Trip No. 2 - Excursion to the Brunswick #6 and #12,
Caribou, and Restigouche Base-Metal deposits and
regional geological setting, Bathurst Mining Camp,
Northern New Brunswick
Trip No. 3 - Gold Deposits Associated with Felsic
Intrusions in Southwestern New Brunswick
Trip No. 4 - Niobium Mineralization in Niocan’s S-60 Zone,
Oka Carbonatite
Trip No. 5 - Volcanic Construction and Gold-Rich Deposits
of the Doyon-Bousquet-LaRonde Mining Camp
Trip No. 6 - The Matagami Mining Camp
Las Médulas
David R. Lentz
Department of Geology, University of New Brunswick, Fredericton, NB
Las Médulas is one of UNESCO’s 730 World Heritage Sites (WHS)
and one of now 37 WHS in Spain; Spain has the most WHS of any
country in the world. Accepted in 1997 into the WHS list, Las Médulas
is a spectacularly preserved alluvial gold mining area (2000 hectares)
with more than 50 archaeological sites recorded. It is located 20 km
WSW of Pontferrada and just south of Lake Carucedo and is accessed
through the town of Carucedo. Wonderful landscape and architecture
typify the region, and numerous museums have information on Las
Médulas. Two routes exist, one to Las Médulas near the base of the
“deposit” and one to the top of the remaining mountain and deposits
through the historic village of Orellán; the latter route provides a spectacular view from Mirador de Orellán of the remains of the mined
mountain with a reddish glow that is particularly accentuated by the
late afternoon to evening sunset. Details of this archaeological site are
rarely in English and French, although both English and French booklets on Las Médulas and the region have been produced by Junta de
Castilla y León; much of this information is gleaned from that book by
D.G. López, P. Lozano, and M. Sánchez and from a site visit. There is
abundant information in Spanish on various websites and links through
UNESCO’s WHS list.
During the reign of Augustus, the Roman Empire went to a gold
standard (7.8 gram gold coin, aureus), thus increasing the demand for
the metal. The Asturs, the last people to be enslaved by the Romans in
Spain & Portugal, were forced to mine various parts of their region;
Las Médulas was probably the largest gold mining area in the Roman
Empire for almost 200 years, ending in the early part of the 3rd century
AD; it contributed over 5% to the Roman treasury.
The alluvial gold deposits are hosted in the conglomeratic parts of the red Miocene fluvial (or glacial-fluvial) deposits; gold-bearing quartz, dust,
platelets, and nuggets were described. Obviously,
these deposits formed from the intense weathering
and subsequent erosion of Hercynian gold deposits
that are famous in northwestern Spain. In fact following the historical areas of mining by the Asturs during Roman times has lead to more recent gold discoveries in the region. The geographer and naturalist,
Pliny the Elder (who died near Pompeii in the 79 AD
eruption of Vesuvius); his nephew (Pliny the
Younger) recorded the “Plinian” eruptions from the
west of Vesuvius) noted in his book Naturalis Historia that this region supplied over 6500 kilograms of
gold per year. In the same book, Pliny detailed the
mining methods of the region, which included building huge canals (400 kms of canals) from the moun-
January 2003 – Gangue No. 76
tain tops and rerouting rivers (River Oza) so as to wash the mined material into the panning fields near the town at the
base of the mountain, Las Médulas. Between 100 and 230 million m3 were mined from the area and tailing heaps typify
the lower regions. Interestingly, this was one of the main arguments against making this a WHS, because it was argued
that it represented the ecological destruction of the region, although it is definitely not like other historical mining areas
with exposed sulphides to contend with. Rather, what is left is a snapshot of the region’s mining heritage and economic
endowment, albeit at the hand of their Roman captors, where wealth was created for the Romans at the expense of the
people of the region. Much earlier estimates indicated about 1 ppm gold per tonne, with up to 10 ppm (probably locally),
although recent average estimates are much lower near 50 mg/ m3 (several hundred ppb); therefore estimates of the
amount of gold extraction would be much lower. Mining ended abruptly as a result of the problems in the Roman Empire and the change from the gold currency standard.
January 2003 – Gangue No. 76
January 2003 – Gangue No. 76
SYMPOSIA
SUSTAINABLE DEVELOPMENT IN THE MINERAL RESOURCES SECTOR: AN OXYMORON OR GOLDEN
OPPORTUNITY? - Jeremy Richards (University of Alberta). Sponsored by SEG, GAC and MAC.
METALS IN THE ENVIRONMENT
Bill Price (British Columbia Ministry of Energy and Mines) and John Jambor (University of British Columbia, and
Leslie Research and Consulting). Sponsored by MAC.
GIS: A LEADING EDGE FOR GEOSCIENTISTS IN THE 21ST CENTURY
Jeff Harris (Geological Survey of Canada) and Danny Wright (Geological Survey of Canada).
Sponsored by GIS Division (GAC).
SPECIAL SESSIONS
MASSIVE SULPHIDES ON THE EDGE: THE FORMATION OF VMS AND SEDEX DEPOSITS WITHIN EVOLVING
CONTINENTAL MARGINS — Steve Piercey (Laurentian University) and Jim Mortensen (University of British
Columbia). Sponsored by Mineral Deposits Division (GAC) and SEG.
TECTONIC CONTROLS ON PALEOPROTEROZOIC MINERALIZATION
Chris Beaumont-Smith (Manitoba Industry, Trade and Mines, Geological Survey Branch), Alan Bailes (Manitoba
Industry, Trade and Mines, Geological Survey Branch) and Alan Galley (Geological Survey of Canada).
Sponsored by Precambrian Division (GAC).
CANADIAN DIAMOND DEPOSITS: HISTORY AND TECHNIQUES OF THEIR DISCOVERY
Felix Kaminsky (KM Diamond Exploration Ltd. and University of British Columbia). Sponsored by SEG & MAC.
NEW PERSPECTIVES ON THE EVOLUTION OF THE PLATINUM GROUP ELEMENTS IN MAGMAS
AND ORE DEPOSITS - James Scoates (University of British Columbia) and David Peck
(Anglo American Exploration) Sponsored by SEG and Mineral Deposits Division (GAC).
ORE-FORMING PROCESSES IN THE PORPHYRY COPPER (GOLD) AND EPITHERMAL GOLD ENVIRONMENTS:
WHAT DO WE REALLY KNOW? - Stephen Rowins (University of British Columbia) and Anthony WilliamsJones (McGill University). Sponsored by SEG, Mineral Deposits Division (GAC), and MAC.
WORKSHOPS
SEG WORKSHOP: UNDERSTANDING GEOPHYSICAL INVERSIONS FOR MINERAL EXPLORATION
Instructors: Douglas Oldenburg and Francis Jones (The University of British Columbia - Geophysical Inversion
Facility). Sponsored by the Society of Economic Geologists
SHORT COURSES
THE ANALYSIS AND INTERPRETATION OF FLUID INCLUSIONS (May 24 - 25, 2003)
Organizers: Iain Samson (University of Windsor), Alan Anderson (St. Francis Xavier University,
and Dan Marshall (Simon Fraser University). Sponsored by MAC
ALKALINE Cu-Au PORPHYRIES AND Fe-OXIDE Cu-Au DEPOSITS: DISTINCT DEPOSIT TYPES, A CONTINUUM
OR GENETIC LINKAGE? (May 24 - 25, 2003)
Organizers: Dick Tosdal, Moira Smith and Murray Hitzman. Sponsored by GAC-MDD and MDRU
January 2003 – Gangue No. 76
January 2003 – Gangue No. 76
Short Course Announcement:
ALKALINE Cu-Au PORPHYRIES AND Fe-OXIDE Cu-Au DEPOSITS: DISTINCT
DEPOSIT TYPES, A CONTINUUM OR GENETIC LINKAGE?
Vancouver, B.C., May 24-25, 2003 (immediately preceding the GAC-MAC-SEG Joint Annual Meeting)
Organizers: Dick Tosdal ([email protected]), Moira Smith ([email protected]),
Murray Hitzman ([email protected])
Sponsored by: MDD-GAC and MDRU
Fe-oxide Cu-Au deposits and alkaline porphyry systems can share a number of characteristics,
including overlaps in mineralogy, geochemistry and alteration types. A number of deposits, including
Lorraine (BC), Rio Grande (Argentina) and Yerington District (Nevada) appear to share attributes of
both deposit types. This 2 day short course will be presented by some of the leading researchers in
porphyry and Fe-oxide Cu-Au deposits, and will explore the similarities, differences and possible
linkages between the two. We will have space available for posters and rock specimens, open to all
who wish to contribute.
Please visit the GAC-MAC Vancouver 2003 website www.vancouver2003.com or contact one
of the organizers for details.
Irish Carbonate Hosted Zinc-Lead deposits: 4-6 September 2003; Rehabilitation of
mine site: 4-6 September 2003; Iberian Pyrite Belt: 4-6 September 2003; South Greenland:
20-27 August 2003 (Pre-conference)
)LH
)LHOO G 7ULSV
For general information on accommodation and registration, please contact:
Nicola Meenan, Conference Partners Ltd.
96 Haddington Road
Ballsbridge
Dublin 4, Ireland
Tel: +353 1 6677188
Fax: +353 1 6643701
E-mail: [email protected]
January 2003 – Gangue No. 76
January 2003 – Gangue No. 76
MEETINGS, WORKSHOPS, & FIELDTRIPS
2003
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•
•
•
•
•
•
•
•
•
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•
February 24- 26 - Society for Mining, Metallurgy and Exploration (SME) Annual Meeting, Cincinnati, OH, USA; Tel: (800) 763-3132; email: [email protected]
March 9 - 12 - Prospectors and Developers Association of Canada (PDAC) Meeting, Toronto,
Ontario, www.pdac.ca; email: [email protected]
March 26 - 30 - N.E. Section GSA and Atlantic Geoscience Society, Metallogeny of the Northern Appalachians, Westin
Hotel, Halifax, Canada; www.geosociety.org; Contact: [email protected]
April 26-28 - Third Annual Workshop in Mineral Exploration: Gold Exploration, Sponsored by Laurentian University
SEG Student Chapter; http://laurentian.ca/geology/SEG; contact: Natalie Lafleur-Roy; email: [email protected]
May 3-11 - Field Environmental Geochemistry Course, Iberian Pyrite Belt, Portugal and Spain, http://www.segweb.
org/IberianCourse.htm
May 4 - 7 - CIM Montreal 2003 Annual General Meeting, Montreal, Quebec; Website: www.cim.org
May 18 - 24 - 39th Forum on the Geology of Industrial Minerals, Nevada Bureau of Mines and Geology, Nevada Division of Minerals and Nevada Mining Association. www.nbmg.unr.edu/imf
May 25 - 28 - GAC-MAC/SEG Joint Annual Meeting, Vancouver, BC. www.Vancouver2003.com
August 24 - 28 - 7th Biennial Society for Geology Applied to Mineral Deposits (SGA), Contact: Demetrios Eliopoulos,
Inst. of Geology and Mineral Exploration, Greece; email: [email protected]
August 29-Sept 3 - IGES/NAMS 2003: 21st International Geochemical Exploration Symposium (IGES) and 3rd
North Atlantic Minerals Symposium (NAMS), University College, Dublin, Ireland; http://www.aeg.org
September 24-25 - CIM Field Conference: Ore Deposits at Depth-Challenges and Opportunities, Timmins, Ontario
Contact: Mr. Damien J. Duff, Falconbridge Limited, Timmins, Ontario; email: [email protected]
November 2-5 - Geological Society of America (GSA) Annual Meeting, Seattle, WA, USA; http://www.geosociety.org/
2004
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•
May 15-17 – GAC/MAC Annual Meeting, Brock University, St. Catharines, Ontario
August - IGC Italia 2004 - 32nd International Geological Congress, Florence, Italy
NORTHEASTERN SECTION -GSA and ATLANTIC
GEOSCIENCE SOCIETY (AGS) meeting
38th Annual Meeting
Westin Hotel, Halifax, Nova Scotia, Canada
March 27-29, 2003
5 Field Trips, 3 Short Courses,
1 Workshop, 5 Symposia, 12 Theme
Sessions, plus more!
DETAILED INFORMATION
For further information, see www.geosociety.org, contact the General CoChairs Marcos Zentilli, [email protected], and David B. Scott,
[email protected] or Administrative Assistant Jane Barrett, jane.
[email protected], Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 3J5; Tel: (902) 494-2358, Fax: (902) 4946889.
January 2003 – Gangue No. 76