Olympic Dam Geology New Insights

Transcription

1 Olympic Dam Geology New Insights Kathy Ehrig (Superintendent Geometallurgy) and Jesse Clark (Senior Mine Geologist) South Australian Exploration and Mining Conference RD m

2 Disclaimer Forward-looking statements This presentation contains forward looking statements, which may include statements regarding plans, strategies and objectives of management, future performance and future opportunities. These forward looking statements are not guarantees or predictions of future performance, and involve known and unknown risks, uncertainties and other factors, many of which are beyond our control, and which may cause actual results to differ materially from those expressed in the statements contained in this presentation. BHP s Annual Report on Form 20-F filed with the US Securities and Exchange Commission identifies, under the heading Risk Factors, specific factors that may cause actual results to differ from the forward-looking statements in this presentation. BHP does not undertake any obligation to update or review any forward-looking statements. No offer of securities Nothing in this presentation should be construed as either an offer to sell or a solicitation of an offer to buy or sell BHP securities in any jurisdiction, or be treated or relied upon as a recommendation or advice by BHP. 2

3 Acknowledgements BHP Olympic Dam +120 geoscientists who have worked at Olympic Dam University of Tasmania Dima Kamenetsky Jocelyn McPhie Maya Kamenetsky Olga Apukhtina- completed PhD 2016 Qiuyue Huang- completed PhD 2016 Alexander Cherry completed PhD 2018 PhD Students: Matthew Ferguson, Nathan Chapman CODES Laser Ablation Facilities University of Melbourne- Roland Maas CSIRO Land and Water, Adelaide- Mark Raven Geological Survey South Australia- Alan Mauger ARC Linkage LP The supergiant Olympic Dam uranium-copper-gold rare earth element ore deposit: towards a new genetic model University of Adelaide Nigel Cook Cristiana Ciobanu Edeltraud Macmillan- completed PhD 2016 (works for BHPB OD) Alkis Kontonikas-Charos- completed PhD 2017 Sasha Krneta- completed PhD 2017 PhD Students: Liam Courtney-Davies, Max Robert Verdugo Ihl, Marija Dmitrijeva, William Keyser, Danielle Schmandt, Mark Rollog Adelaide Microscopy South Australian Mining and Petroleum Services Centre of Excellence (Department of State Development) Trace elements in iron oxides project Copper Uranium Hub project (joint ARC project IH ) 3

4 Olympic Dam Cu-U-Au-Ag Deposit - Summary Modified after Ehrig et al. (2012) work in progress Key Points no surface expression of the deposit concealed by ~350m of unaltered cover sequence tectonic-magmatic-hydrothermal breccia-hosted Fe-oxide Cu-U-Au- Ag deposit (IOCG-U type) Olympic Dam Breccia Complex (ODBC) footprint ~50 km 2. hosted within the ~1593 Ma Roxby Downs Granite (RDG) deposit footprint ~6 km x 3 km x 800 m unequivocal spatial correlation between Fe, Cu, U 3 O 8, Au, and Ag across the deposit due to the co-precipitation of these elements Deposit-wide Mineralogical Zonation progressive increase in Fe from edge to centre Fe-oxide alteration (Fe +2 Fe +3 ). magnetite + apatite + chlorite hematite + sericite py cp bn cc siderite fluorite barite polymetallic Zn-Pb-Ag and granite-related Mo-Sn-W uraninite - coffinite brannerite three styles of gold mineralisation 4

5 Geological Map ~-350mRL pre-2018 version work in progress Ehrig et al. (2012) Modified after Ehrig et al. (2012) 5

6 Felsic / mafic-ultramafic rocks and bedded clastic facies RDG GRV-F MDY work in progress KASH KHEMQ VBx VASH KFMU HEMQ Modified after Ehrig et al. (2012) 6

7 ~1590 Ma felsic/mafic/um rocks components in BCF RDG KHEMQ VASH CA-ID-TIMS: zircons Ma ± 0.21 Ma CA-ID-TIMS: zircons ± 0.58 Ma GRV-F LA-ICPMS: zircons ± 6.9 Ma KASH CA-ID-TIMS: zircons Ma ± 0.30 Ma LA-ICPMS: zircons ± 7.4 Ma MDY GRV-UM KFMU LA-ICPMS: apatite ~1590 Ma Huang et al (2016) LA-ICPMS: zircons ± 11 Ma Cherry et al (2018): zircons 7

8 Progressive brecciation and alteration of RDG work in progress RDG ~3% Fe HEMQ Modified after Ehrig et al. (2012) 8 ~60% Fe

9 Brecciation and Fe-alteration Textural Inversion RDG KHEMQ VASH GRV-F HEMQ brecciation & Fe-alteration KASH MDY GRV-UM KFMU 9

10 OD Deposit Setting: DATA Driven Change in Ideas 1990s 2010s early early 1980s 1980s 1990s 2010s Oreskes and Einaudi (1990) Roxby Management Services (1980s) modified Haynes et al. (1995) McPhie et al. (2011, 2016), Cherry et al. (2018) 10

11 OD Deposit Setting: DATA Driven Change in Ideas early 1980s early 1980s : Surface drilling only Roxby Management Services (1980s) Roberts and Hudson (1983) 11

12 OD Deposit Setting: DATA Driven Change in Ideas 1990s 1990s : Underground drilling : Surface drilling Oreskes and Einaudi (1990) modified Haynes et al. (1995) 12

13 OD Deposit Setting: DATA Driven Change in Ideas 2010s 2010s : Underground drilling : Surface drilling McPhie et al. (2011, 2016), Cherry et al. (2018) 13

14 Perspective is everything 6 Blind Men and the Elephant Story 6-blind-men-and-the-elephant-the-story-of-concussion 14

15 Our understanding has evolved, and continues to evolve : Underground drilling : Surface drilling work in progress Modified after Ehrig et al. (2012) 15

16 Long-section: NW-SE NW cover sequence unconformity Au > 1 ppm SE Cu > 1 wt% 500 m Jubilee Fault (locally Mashers Fault) Woodall Faults 16

17 Copper distribution Evidence of major faulting -350mRL -500mRL -650mRL Cu (wt%) 17

18 Quantitative Barite-Fluorite-Siderite (-350mRL) bar (wt%) flu (wt%) sid (wt%) 18

19 Woodall Fault Series evidence for >2.5 km of vertical offset work in progress The outer margins of the ODBC are defined by the last occurrence of biotite when progressing from fresh RDG into the deposit. altered RDG does occur in the area label as RDG, but biotite does not occur within the ODBC. in the northern part of the ODBC, transition from >5% Fe contour to the edge of the ODBC occurs over lateral distances of at least 2-3 kms. In the southern ODBC, this transition occurs over a distance <500m 1km. Reasonable to expect an alteration envelop of several kms wide around the deposit. Possible explanations: fault with at least several kms of lateral offset, but no preserved evidence of this in the regional geophysics RDG south of the ODBC was uplifted at least 2-3km relative to the ODBC. This also helps to explain why BCF near the southern margin of the ODBC occurs at a depth >1800m. Modified after Ehrig et al. (2012) 19

20 Woodall Fault Series >2.5 km of vertical offset A B work in progress B A Modified after Ehrig et al. (2012) 20

21 A bit of a conundrum brecciated, qtz-rich sandstone (Olympic Dam) post-1590 Ma units deep within the ODBC? How is this possible? RD2751 and RD1628 Pandurra-like Acropolis, Emmie Bluff, Oak Dam, Wirrda Well SAE6 Emmie Bluff RD m Cherry et al (2017) RD RD2751

22 Olympic Domain Mesoproterozoic to Cambrian Cover modified from Paterson (1986) flat lying, undeformed, unaltered, not mineralised helps to constrain fault re-activation at Olympic Dam can be variably mineralised Tapley Hill Formation (age = Sturtian) Pandurra Formation (~1490 Ma)* *Beyer et al (2018) Gairdner Dyke Swarm ~827 Ma thickness of the Whyalla Sandstone, Tapley Hill (TPF) and Pandurra Formations (PF) vary from absent to > 1 km. TPF and PF not preserved in the cover sequence above Olympic Dam. partially preserved at Wirrda Well, Acropolis, Oak Dam. Not to scale 22

23 Insight from the Cariewerloo Basin Cariewerloo Basin rift origin proposed by Beyer et al (2018) ~1500 Ma - rift initiation ~1490 Ma oldest diagenetic illite in Pandurra ~1440 Ma possible fault re-activation, far-field Kararan tectonism major fluid fluxes during Albany-Frazer orogeny and Musgravian orogenesis ~1.1 Ga - possible uplift/exposure of Pandurra ~686 Ma Pandurra probably re-buried, post-sturtian sediment loading on the Stuart Shelf. Beyer et al (2018) Mesoproterozoic rift sedimentation, fluid events and uranium prospectivity in the Cariewerloo Basin, Gawler Craton, South Australia 23

24 Conclusions Olympic Dam is a dismembered deposit Present orebody geometry does not reflect pre-mineralisation structural architecture rather remnants. Initially, at ~ Ma: intense, texturally destructive alteration and brecciation, and mineralisation Multiple regional- and local-scale deformation events spanning over 1 billion years ( Ga) Major sinistral wrench structural event at ca Ma(?); scale of vertical displacement unresolved. Major fluid remobilisation events corresponding to major supercontinental cycles, particularly orogenic events Complex geometries can be resolved by structural events that dislocate or rotate faulted blocks RD m 24

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