PROTEROZOIC GOLD

PROTEROZOIC GOLD Vic Wall Vic Wall and Associates Steve Massey Western Geoscience Greg Hall Golden Phoenix Interna;onal REFERENCE Wall, V. J. 2005. TAG Thermal Aureole (Pluton related) Gold Systems. AIG journal February Granites-­‐Tanami: features •  Major Proterozoic gold province –  NT-­‐WA border area, Central Australia •  300km. (E-­‐W) x 200km. (N-­‐S) –  15-­‐20Moz. Au resources + produc;on –  current produc;on ~400-­‐500Koz. Au pa. –  several mul;million ounce deposit clusters •  The Granites, Dead Bullock Soak, Callie, Tanami •  styles good grade Granites-­‐Tanami: deposits (Callie: +5mozs)
Granites-­‐Tanami: features •  Recent discoveries (Old Pirate, Buccaneer) •  Ground access difficul;es –  major ground posi;ons –  na;ve ;tle –  remote •  Poorly exposed & mapped, but good regional geophysical datasets Granites-­‐Tanami: methodology •  Data integra;on –  aeromagne;c –  regional gravity –  regional geology –  mineral occurrences –  current tenure •  Regional geological interpreta;on •  Targe;ng –  empirical explora;on model –  TAG model Granites-­‐Tanami: regional geology •  Similar to Pine Creek and analogies with Hall’s Creek, but –  regional WNW strike of Palaeo-­‐Proterozoic –  flat, deeply weathered, windblown cover widespread Pine Creek: geology Pine Creek: plutons, structures & magne;cs Granites-­‐Tanami: regional geology •  Deposi;onal ages •  Archaean/Early Prot. gneissic basement •  circa. 1900Ma. metasediment-­‐dominated succession •  Deforma;on •  ~1860Ma, slate-­‐belt style, NNE-­‐SSW shortening – shallow dipping regional enveloping surface •  accompanied by lower greenschist metamorphism •  minor subsequent deforma;on, except around plutons Granites-­‐Tanami: regional lithostra;graphy Granites-­‐Tanami: RTP Y#Y#
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Granites-­‐Tanami: regional geology •  Plutonism –  1810-­‐1820Ma –  reduced, frac;onated I-­‐type suite –  emplaced 6-­‐10kms. depth •  Related broad thermal aureoles –  metamorphic & gravity evidence: •  extensive pluton roof zones •  Intrusion accompanied by, around/above pluton margins –  higher strain zones & faul;ng •  steep stretching linea;on (high temperature) •  brigle faults (lower temperature/mmic. grade) –  upwarping/doming of stra;graphy Tanami area: Y#
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Granites-­‐Tanami: geology model Granites-­‐Tanami: key deposits & geology •  ‘The Granites’ cluster –  hosted by iron forma;on/pelite package –  in high temperature, high strain zone •  proximal and subparallel to and wrapping around granitoid pluton margin (~E-­‐W trending) –  short strike length (<300m), long down plunge extent of ore zones/lenses •  7-­‐15g/t Au, average 11g/t Au underground grades •  bulk mineable widths –  bedding subparallel carbonate-­‐quartz & calc-­‐silicate veining •  related gold, arsenopyrite, pyrrho;te enrichment –  similar lithologies & parageneses to Musselwhite, Lupin, etc Cerberus Mi
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Dead Bullock Soak geology Callie geology Callie: Cross sec;on Callie lithologies Granites-­‐Tanami: key deposits & geology •  Callie (>7Moz.Au) –  hosted by reduced (carbonaceous) metasediments –  in faulted an;formal hinge zone (~E-­‐W trending) –  bedding subparallel-­‐ & steep quartz-­‐rich veinlet system •  7-­‐10g/t, bulk mineable widths –  moderate temperature •  bio;te stable, weak altera;on in metasediment hornfels –  in pluton roof zone above & structures subparallel to pluton margin –  Musselwhite-­‐like structural semng Callie area: bouger gravity/ RTP Avon
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Pluton-­‐related (Thermal Aureole) Gold 6
2
1
Ì
3
5
2
4
5km
GRANITOID INTRUSIONS
THERMAL AUREOLE
COUNTRY ROCKS
KEY STRUCTURAL ZONES
1
2
3
4
5
6
GOLD DEPOSIT SETTINGS
Fort Knox
Sukhoi Log, Kumtor
Pogo, Vasilkovskoye
Granites-Tanami
Muruntau
Obuasi, Telfer
TAG: Western Australia •  Telfer, >30 Moz. Au (-­‐Cu) deposit •  bedding parallel veins; discordant stockworks, breccias •  high grade quartz-­‐carbonate-­‐pyrite-­‐chalcopyrite veins –  hosted by ?mid Proterozoic siliciclas;c succession with some carbonates & evaporites –  fold-­‐thrust compressional deforma;on & greenschist metamorphism; •  reac;va;on of basement structures –  felsic pluton/batholith emplacement •  post main regional deforma;ons •  ~620Ma., similar isotopic age to Au mineraliza;on •  frac;onated I-­‐type suites Telfer Au-­‐Cu deposit Telfer: district geology TAG: Western Australia •  Telfer deposit localised in –  pluton roof zone (above pluton edge?) •  regional gravity signature •  note map pagern, nearby skarns & other pluton proximal deposits –  outer aureole semng –  mul;ply plunging, asymmetric, an;clinorial ‘domal’ structures •  reac;vated fold-­‐(blind) thrust system –  dila;on along bedding controlled by stra;graphy, small thrusts –  dila;on in discordant zones, related to small scale fault-­‐fold systems –  favourably thin-­‐bedded stra;graphy, in over more than 1km. thickness •  higher temperature altera;on & higher Cu with increasing depth •  highly saline fluids Telfer ‘dome’ Telfer cross secCon Telfer: ore zones Telfer: structural geology Telfer: structural interpretaCon Telfer gravity magne;c image W.A.
N.T.
Pluton-­‐related (Thermal Aureole) Gold 6
2
1
Ì
3
5
2
4
5km
GRANITOID INTRUSIONS
THERMAL AUREOLE
COUNTRY ROCKS
KEY STRUCTURAL ZONES
1
2
3
4
5
6
GOLD DEPOSIT SETTINGS
Fort Knox
Sukhoi Log, Kumtor
Pogo, Vasilkovskoye
Granites-Tanami
Muruntau
Obuasi, Telfer
Telfer bouger gravity Where next? W.A.
N.T.
PROTEROZOIC GOLD Vic Wall Vic Wall and Associates Steve Massey Western Geoscience Greg Hall Golden Phoenix Interna;onal