Gidji Lake formation -

Transcription

1 Gidji Lake formation - Key Stratigraphic marker for World Class Gold Deposits of Kalgoorlie Presentation to CSIRO - July 2017 Please reference this document if the slides, figures or concepts are to be used externally: Tripp, G I, Stratigraphy and Structure in the Neoarchaean of the Kalgoorlie district, Australia: Critical Controls on Greenstone hosted Gold Deposits, PhD thesis (unpublished), James Cook University, Townsville.

2 Kalgoorlie Stratigraphy Major field program initiated by Placer Dome (2004), advanced by Barrick (2007) Key thing is we held most of the ground Principal new data sets: Geological mapping (John Crossing et al.) re-logging drill chips (2 senior geologists +2 years) lithogeochemistry (Halley + team) stratigraphic/structural core logging (Barrick) regional geophysics (John Coggan) structural analysis targeted geochronology Key Goal: make a FORMATION MAP from an extensive and detailed lithology map

3 Kalgoorlie Stratigraphy Major field program initiated by Placer Dome (2004), advanced by Barrick (2007) Key thing is we held most of the ground Principal new data sets: Geological mapping (John Crossing et al.) re-logging drill chips (2 senior geologists +2 years) lithogeochemistry (Halley + team) stratigraphic/structural core logging (Barrick) regional geophysics (John Coggan) structural analysis targeted geochronology Key Goal: make a FORMATION MAP from an extensive and detailed lithology map

4 Kalgoorlie Stratigraphy Major field program initiated by Placer Dome (2004), advanced by Barrick (2007) Key thing is we held most of the ground Principal new data sets: Geological mapping (John Crossing et al.) re-logging drill chips (2 senior geologists +2 years) lithogeochemistry (Halley + team) stratigraphic/structural core logging (Barrick) regional geophysics (John Coggan) structural analysis targeted geochronology Key Goal: make a FORMATION MAP from an extensive and detailed lithology map

5 Gold Camps ~100 Moz Au within 50 km radius of Kalgoorlie

6 Kalgoorlie a World Class gold district >100 Million ounces of gold from 8 mining camps in a 50 km radius Major camps include: Golden Mile Moz; Kambalda +12 Moz; Kanowna - +7 Moz; Kundana Moz; New Celebration +5 Moz ; Mount Pleasant - +3 Moz; Mount Monger +2 Moz-; Binduli - +2 Moz; Ora Banda +2 Moz and many other small occurrences that contribute to the total endowment. Robert et al. (2005) three recurring host-rock associations account for a majority of large Archaean Gold deposits globally: 1. Iron-rich mafic igneous rocks, 2. Iron-rich sedimentary rocks, and 3. Felsic to intermediate porphyry stocks and dikes Iron-rich rocks: high Fe / (Fe + Mg) content, are chemically favourable hosts (Fe-enriched dolerite, high-fe tholeiite, banded iron formation) Iron rich layers within differentiated dolerite sills and sedimentary rocks have a combined ironenrichment and rheological competence contrast Felsic intrusions, and the sedimentary rocks they intruded, can also host world class gold deposits - so Fe enrichment is a bonus, but not exclusive, and suggests that more fundamental processes are in play than just the host rock chemistry

7 Kalgoorlie district Max Au in drilling 2004 (>480,000 holes)

8 Kalgoorlie district Max As in drilling 2004 (>480,000 holes)

9 Stratigraphy, Structure and Gold Exploration So Why? Is the key question Why is almost half of the gold endowment of the EGP contained within 50 Km of Kalgoorlie? Majority at Fimiston.. ± Kanowna, HBJ and Victory-Defiance Placer and Barrick programmes were about understanding the geochemical, stratigraphic and structural features that coincide with major gold deposits PLACER: factual data collection field mapping, drill hole re-logging, lithogeochemistry, geophysics, 3D modelling FOR TARGETING BARRICK: stratigraphy to make a FORMATION MAP, identify major unconformities, exploit all previous high quality data sets to PROVIDE TARGETS

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11 Stratigraphy is key What do the favourable units look like, and where are they? There is a spatial relationship between World Class gold deposits and an unconformity in the the Black Flag Group A A

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14 Early Deformation Map-scale D1 deformation coincident with the two largest gold accumulations in Kalgoorlie

15 Early Deformation Map-scale D1 deformation coincident with the two largest gold accumulations in Kalgoorlie

16 Early Deformation Map-scale D1 deformation coincident with the two largest gold accumulations in Kalgoorlie

17 Kurrawang Unconformity Most important structural relationship in the Kalgoorlie district is that the Kurrawang unconformity, overprints F2 folded greenstones, Kurrawang is subsequently folded by F3 folds with an axial plane foliation S3

18 Kurrawang Unconformity Most important structural relationship in the Kalgoorlie district is that the Kurrawang unconformity, overprints F2 folded greenstones, Kurrawang is subsequently folded by F3 folds with an axial plane foliation S3

19 The Conglomerate/Gold relationship Spatial relationships between late clastic unconformable conglomerate and major gold districts documented in all Neoarchaean terranes globally Western Australia: Kurrawang Abitibi: Timiskaming LVGF: Kavirondian Dharwar: Palkanmardi Late clastic rocks mark the onset of orogenesis in greenstone belts (Robert et al. 2005) developed as syn-orogenic basins demonstrated by strong linear distributions of lithofacies with major fault controls on at least one margin (Krapez et al. 2010)

20 Three possible explanations SEALS late clastic sequences covered a much wider lateral area than the present day linear remnants; major gold deposits located in the upper parts of the greenstone stratigraphy, sedimentary rocks acted as a sub-regional hydrothermal seal ; allowed upper greenstone segments to overpressure, fracture and release magmatic sourced, metal rich oxidised fluids that would mix with basinal reduced fluids MAJOR FAULTS major shear zones controlled the linear distribution of late clastic rocks, and conglomerate-gold relationship could be one in which the fault-preserved conglomerate remnants identify major crustal-tapping structures that were long-lived and controlled major fluid flow and gold precipitation. Linear distribution of gold deposits within a certain proximity to major shear zones is an empirical criterion commonly applied in exploration for gold deposits (Groves 2000; Weinberg et al. 2004) PRESERVATION areas with the youngest stratigraphic units have the potential to preserve the thickest sections of greenstone stratigraphy. In many Archaean sequences worldwide, the presence of multiple mineralisation styles and timings is well documented. Since those styles include some syngenetic deposits and high-level intrusion-related systems, the potential to preserve early mineral systems will require extensive depocentres that were not significantly eroded during the orogenic phase, and the presence of thick sequences of the youngest syn-orogenic sedimentary rocks will identify those areas of preferential preservation.

21 SUMMARY: The Conglomerate/Gold relationship Remnant unconformable late coarse clastic rocks indicate stratigraphic preservation and potentially preservation of early formed mineralisation components (at a REGION scale) EGP (Kurrawang Unconformity) Abitibi (Timiskaming Unconformity) Lake Victoria Goldfields (Kavirondian Unconformity) Dharwar India (Palkanmardi Unconformity) But at a CAMP scale, there is an earlier stage unconformity that has spatial association with major gold deposits; Golden Mile/Kanowna Belle/Binduli; also documented at Gokona,Tanzania LVGF (6 Moz; Lower to Upper Nyanzian unconformity Au in vein clasts in conglomerate) IMPLICATION: Major gold camps have multiple mineralisation events in the same geographic area separated by time and geological events = fundamental and long-lived structural controls, revealed by the stratigraphy

22 Binduli two distinct gold events Au.Ag.Bi.Te.Zn (±Mo.Pb.Hg)

23 Centurion Mine Two main ore styles

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27 Kanowna Belle Two stage mineralisation Red Hill, Robinsons, BLC, White Feather, Palaeochannels KANOWNA BELLE Carbonate vein hosting tellurides and free gold L Red Hill Post foliation orogenic flat veins

28 Kanowna Belle Au > Ag, Mo, Te, As, Bi, V Rogers et al. (2004) 0 GEOLOGICAL LEGEND : Golden Valley Conglomerate QED Rudite Footwall Grit Grave Dam Grit Lowes Sandstone Ultramafics Hangingwall Basalt Aphyric Intrusion Kanowna Belle Porphyry Fault Shears Open Pit Benches MINERALISATION > 4g/t Au 1-4g/t Au 200m

29 Multiple timings of mineralisation Kanowna Belle 1. Epithermal Au clasts in footwall conglomerate 2. Stockwork vein and disseminations in KB Porphyry; Crustiform Au-Te carbonate veins and breccias 3. Folded Au-Te carbonate veins with S3 axial planar cleavage, and syn-d3 pressure shadow and fracture gold 4. Late Red Hill flat veins

30 1. Epithermal Au clasts in footwall conglomerate 2. Stockwork vein and disseminations in KB Porphyry; Crustiform Au-Te carbonate veins and breccias 3. Folded Au-Te carbonate veins with S3 axial planar cleavage, and syn-d3 pressure shadow and fracture gold 4. Late Red Hill flat veins

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32 Early stockwork overprinted by Au-Te carbonate breccia

33 Golden Mile Fe-rich rocks (Mount Charlotte, Mount Percy, Hannan s North) Golden Mile Dolerite the most important Archaean Greenstone gold host-rock on the planet Metal signature - Au > Ag, Te, V, Hg Differentiated mafic intrusion with a favourable layer of Fe-rich quartz dolerite Fimiston contains the bulk of the gold in early deformed breccia zones and veins >55 Moz Mount Charlotte vein stockworks ~6 Moz Mount Percy porphyry hosted veinlets ~< 1 Moz Hannan s North crustiform and mesothermal veinlets

34 Long Section (H. Poulsen) Two stage mineralisation Early Fimiston, Late, post foliation Mt Charlotte

35 Multiple timings of mineralisation Golden Mile Early Fimiston crustiform Au-Te veins and breccia lodes deformed by penetrative foliation Late Mt Charlotte qz-carb-au veins cut regional foliation EVENTS BLACK FLAG BEDS Golden Mile Dolerite FP DYKES FIMISTON GOLD HP DYKES QUARTZ-CARBONATE VEINS STEEP REVERSE FAULTS SHALLOW REVERSE FAULTS NNE STRIKE SLIP FAULTS LAMPROPHYRE DYKES Kalgoorlie anticline-syncline 2681+/-5Ma 2675+/-2Ma 2676+/-3Ma NW FOLIATION /-11 Ma Mt-Charlotte 2636+/-4Ma TIME Timing of Fimiston style mineralisation is bracketed between two separate compressional events. Maximum age constrained by Ma plagioclase porphyry dykes, minimum age constrained by 2662 Ma dyke cutting Fimiston vein. Most likely age around close to average age of plagioclase-hornblende porphyry. - L. Gauthier (2007)

36 Multiple timings of mineralisation Golden Mile Early Fimiston crustiform Au-Te veins and breccia lodes deformed by penetrative foliation Late Mt Charlotte qz-carb-au veins cut regional foliation EVENTS BLACK FLAG BEDS Golden Mile Dolerite FP DYKES FIMISTON GOLD HP DYKES QUARTZ-CARBONATE VEINS STEEP REVERSE FAULTS SHALLOW REVERSE FAULTS NNE STRIKE SLIP FAULTS LAMPROPHYRE DYKES Kalgoorlie anticline-syncline 2681+/-5Ma 2675+/-2Ma 2676+/-3Ma NW FOLIATION /-11 Ma Mt-Charlotte 2636+/-4Ma TIME Timing of Fimiston style mineralisation is bracketed between two separate compressional events. Maximum age constrained by Ma plagioclase porphyry dykes, minimum age constrained by 2662 Ma dyke cutting Fimiston vein. Most likely age around close to average age of plagioclase-hornblende porphyry. - L. Gauthier (2007)

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38 Golden Mile Camp

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40 D.Nixon

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43 Mt Charlotte Mueller (2015)

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47 Well known crosscutting between Fimiston and Mount Charlotte ore styles

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49 Gidji Lake formation Early gold event synchronous with volcanism ~2660 Ma Spatial association of unconformity with major gold systems is a potential indicator of syn-volcanic faults

50 Gidji - stratigraphic columns

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52 Gidji Unconformity at the Golden Mile Recent deep drill holes intersected typical Gidji stratigraphy in the south end with (?)paragonitechloritoid flooding alteration of Paringa Basalt

53 Clout (1989)

54 Larcombe (1912) documented intermediate to high sulphidation state mineralogy in the Great Boulder Mine. Early high level mineralisation is mined out Gentle S-plunge of Kalgoorlie Anticline means most of the high level mineralisation was eroded off the system

55 Photos (D. Nixon)

56 Photos (D. Nixon)

57 Photos (D. Nixon)

58 Photos (D. Nixon)

59 Photos (D. Nixon)

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62 Conclusions 1. Spatial association of major gold deposits with unconformity in the Black Flag Group 2. Relationship is more than just spatial syn-volcanic early phase mineralisation 3. Mapping the unconformity defines a search space for syn-volcanic 2660 Ma live faults STRATIGRAPHY is the key for explorers 4. Early high level mineralisation styles of intermediate to high sulphidation state at the Golden Mile (Larcombe) now eroded 5. Overprinting by orogenic phase is crucial to World Class systems multiple events in the same location = fundamental early structures hit again and again