METALLOGENIC MODELS AND GOLD EXPLORATION

Size: px

Start display at page:

Download "METALLOGENIC MODELS AND GOLD EXPLORATION"

Blake Page
5 years ago
Views:

1 METALLOGENIC MODELS AND GOLD EXPLORATION Laurence Robb Dept. of Earth Sciences, University of Oxford, UK

2 RANDGOLD RESOURCES ANNUAL REPORT 2015 THE GOLD CYCLE...BOOM & BUST

3 ...and WHY GOLD? because is still offers such good returns on exploration investment... and although it is rare, it occurs in many different ore deposit types...but represents a challenge to find....after Robert et al., 2007 and Groves et al., 2016

4 GOLD ABUNDANCES... Wedepohl, 1978 Gold deposits 2-10 ppm

5 METALLOGENIC MODELS ARE GREAT...BUT YOU DO NOT WANT TO LOSE YOUR HEAD OVER THEM... THE NEXT MAJOR GOLD DISCOVERIES WILL BE MADE BY GEOLOGISTS WHO THINK OUTSIDE THE BOX

6 METALLOGENIC MODELS FOR GOLD Witwatersrand Basin Murantau Twangiza Murchison Burma Morila Damang Bushveld granites IOCG?? Bin Yauri...after F. Robert et al., 2007

7 OROGENIC GOLD SYSTEMS

8 CRUSTAL CONTINUUM MODEL NOT WIDELY PRESERVED THE NORM DIFFICULT TO FIND...after Goldfarb & Groves, 2015

9 TYPICALLY... Saunders et al., 2014 ORE SYSTEMS ASSOCIATED WITH STEEPLY DIPPING DUCTILE SHEARS (early reverse thrusting; later strike-slip) HOST ROCKS AT VARIOUS MET. GRADES, ORE DEPOSITION ON THE RETROGRADE P-T-t PATH ORES ASSOCIATED WITH QTZ-CARB VEINS; ALTERATION YIELDS ENRICHMENTS IN K, Rb, Na, As, W, Te FLUIDS - MIXED H 2 0-CO 2, LOW SALINITY via METAMORPHIC DEVOLATILIZATION ORE PRECIPITATION RELATED TO PRESSURE FLUCTUATIONS & CO 2 UNMIXING OR FLUID-ROCK REACTION (ph/eh shifts)

OROGENIC GOLD... The Birimian of West Africa Mine / Deposit Million oz Tarkwa 18.9 Damang 3.8 Morila 5.8 Loulo 10.94 Tongon 4.27 Iduapriem 3.5 Obuasi 33.43 Siguiri 4.95 Sabodala 3.51 Yatela 0.

10 OROGENIC GOLD... The Birimian of West Africa Mine / Deposit Million oz Tarkwa 18.9 Damang 3.8 Morila 5.8 Loulo Tongon 4.27 Iduapriem 3.5 Obuasi Siguiri 4.95 Sabodala 3.51 Yatela 0.34 Bibiani 7.32 Syama 7.8 Sadiola ~ 8.0 Lefa 3.87 Ahafo - Including Subika 15.4 Ahafo 9.7 Subika 6.4 Akyem 7.6 Bogoso/Prestea WEST AFRICA PRODUCES ca. 250tpa FROM A RESOURCE BASE >165Moz Au

11 OBUASI...a classic shear zone hosted orogenic Au deposit...over 8km long and 1.5km deep...has produced over 20Moz Au and still has 33Moz remaining

12 MORILA...but the Birimian is not only about conventional orogenic gold... tonalite DAMANG

conglomerates and quartzite Au mineralization is also hosted in and alongside

13 DAMANG... Au mineralization is hosted in palaeoplacer style Tarkwaian qtz-pebble conglomerates and quartzite Au mineralization is also hosted in and alongside sub-horizontal qtz-pyrite veins that introduce gold into the quartzites and overlying phyllites as well as mafic intrusions White et al., 2010 White et al., 2012a,b White et al., 2014

14 DAMANG...detailed IR spectroscopic study utilized to identify and map unusual rock-buffered alteration assemblages in amphibolite grade White et al., 2010

15 White et al., 2010 White et al., 2012a,b White et al., 2014

16 White et al., 2014

17 MORILA... amphibolite grade, flat lying structures and a tabular ore-body that does not crop out on the surface...alteration assemblage indistinct from the country rock HAMMOND ET AL., 2011 RANDGOLD RESOURCES ANNUAL REPORT 2015

18 MURCHISON GREENSTONE BELT, NE MPUMULANGA PROVINCE, RSA Cu-Zn LINE Jaguin et al., 2012,2013 MGB HOSTS 2 DISTINCT STYLES OF MINERALIZATION:- Orogenic style Au-Sb - ANTIMONY LINE VMS style Cu-Zn COPPER-ZINC LINE

19 RUBBERVALE Fm 2970 Ma (Brandl et al., 1996)

20 VMS (Cu-Zn) MINERALIZATION IN RUBBERVALE Fm. AND OROGENIC or INTRUSION RELATED Au MINERALIZATION IN ANTIMONY LINE ARE COEVAL

21 INTRUSION-RELATED GOLD SYSTEMS [IOCG]

22 IOCG...must be the most confused class of mineral deposit types, without a common link in terms of tectonic setting, emplacement level or age connotation... OR IS IT THAT THEY ARE ALL RELATED TO A SPECIFIC FERTILE MAGMA TYPE?...after GROVES et al., 2016

23 BUSHVELD COMPLEX...one of the great metallotects of the World (PGE- Cr-Fe/Ti/V-Cu-Ni)...also has an overlying granitic phase that is the host to numerous polymetallic IOCG like deposits (Fe-Cu-Ag/Au-U)

24 BOSCHHOEK... a high-level Fe-Cu-Zn-Ag-Au system 24

25 INTRUSION-RELATED GOLD SYSTEMS [REDUCED W-Bi-Te] RIRGS

26 Robert et al., 2007 UZBEKISTAN Muruntau 200 Moz ALASKA: Fort Knox 8 Moz Donlin Creek DO THEY OCCUR ELSEWHERE?

27 MURUNTAU... RIRGS The association of Au with Bi-W-Te etc points to a very specific magma source Koneev et al., 2005; IGCP PROJECT 486 Morelli et al., 2007

TWANGIZA-NAMOYA GOLD BELT, DRC (Kivu Provinvce) Kibaran orogenic belt (1300-900 Ma) Sn, W,

Twangiza may also be related to younger intrusions at 750 Ma Au mineralization hosted in folded

28 TWANGIZA-NAMOYA GOLD BELT, DRC (Kivu Provinvce) Kibaran orogenic belt ( Ma) Sn, W, Ta-Nb, Au-Bi mineralization associated with the 975 Ma G4 S-type granites Mineralization at Twangiza may also be related to younger intrusions at 750 Ma Au mineralization hosted in folded Mesoproterozoic sediments and porphyry sills TECHNICAL REPORT PHASE 1 TWANGIZA GOLD PROJECT DRC, 2011 (BANRO)

29 BURMA Potentially one of the most prospective unexplored mineral jurisdiction on the planet Hugely rich in a variety of commodities Au, Pb-Zn, Sn-W, Cu-Ag, Opening up of country prompted re-interest However limited recent geological work

30 Two major orogenic events: W EARLY- MIDDLE PERMIAN Shelf Carbonates Gondwana Sibumasu Palaeo-Tethys SUKHOTHAI ARC Back-Arc Basin Indochina E - Closure of Palaeo- Tethys leading to Indosinian Orogeny LATE PERMIAN 260 MA Shelf Carbonates Sibumasu Palaeo-Tethys SUKHOTHAI ARC Back-arc collapse Indochina LATE TRIASSIC - EARLY JURASSIC MA MAIN RANGE PROVINCE Palaeo-Tethys Sediments Sibumasu SUKHOTHAI ARC Nan Suture Indochina S-Type Chiang Rai Line PALAEO-TETHYS SUTURE -Closure of Neo-Tethys leading to Himalayan Orogeny LATE CRETACEOUS 70 MA India Neo-Tethys WUNTHO- POPA MMM ARC BELT I-Type S-Type MAIN RANGE PROVINCE SUKHOTHAI ARC Chiang Rai Line PALAEO-TETHYS SUTURE Nan Suture Indochina

31 The geology and metallogeny of Burma is dominated by the presence of 2 magmatic arcs:- Wuntho-Popa Arc (I-type, oxidized, Cu-Ag) Mogok-Mandalay-Mergui Belt (S-type, reduced, W-Sn, Au)

32 PALAEO-PLACER GOLD SYSTEMS

mankind (>55 000 t) has come from the Wits Basin.

Phillips,2013 Basin lie in re-examining the prevailing

33 WITWATERSRAND... Over 30% of all the gold ever mined in the history of mankind (> t) has come from the Wits Basin... magnetics Phillips,2013 Does the future of the Wits Phillips,2013 Basin lie in re-examining the prevailing metallogenic models? Lawrie Minter Basal Reef gold and pyrite along foresets octohedral gold crystal in quartz vein, Rose Deep

34 BUT... WHAT HAS BEEN LARGELY OVERLOOKED IS THE SCALE NATURE TIMING OF GOLD REMOBILIZATION IN THE HOST SEDIMENTS

35 ONE FLUID TYPE THAT HAS BEEN OVERLOOKED IN TERMS OF ITS METAL-CARRYING CAPACITY AND EXTENSIVE FLUID PATHWAYS IS AQUEO-CARBONIC AND ASSOCIATED WITH HYDROCARBON FORMATION... Drennan and Robb, 2006 Oberthur, 2013

36 PIXE micro-maps of bitumen nodules suggest that the aqueo-carbonic fluids contained organo-metallic complexes capable of transporting significant quantities of Au, U, Th, As, Fe and Cu Drennan and Robb, 2006

37 THESE AQUEO-CARBONIC FLUIDS COULD HAVE TRANSPORTED GOLD TO A VARIETY OF STRUCTURAL AND/OR CHEMICAL TRAP SITES...

38 METALLOGENIC MODELS & GOLD EXPLORATION MODELS...very useful but need to be applied imaginatively in exploration Conventional exploration models still very applicable, but new discoveries might require looking at things differently... intrusion-related gold in orogenic belts understand IOCG systems better late, extensional, flat-lying structures relationship between exhalative and orogenic processes redox trap sites in palaeo-placer deposits...where ARE THE NEW GOLD TARGETS? Palaeoproterozoic of West Africa - Borborema Central Asian Orogenic Belt Tethyan Orogenic Belt Russian far east

Bulyanhulu: Anomalous gold mineralisation in the Archaean of Tanzania. Claire Chamberlain, Jamie Wilkinson, Richard Herrington, Ettienne du Plessis

Bulyanhulu: Anomalous gold mineralisation in the Archaean of Tanzania Claire Chamberlain, Jamie Wilkinson, Richard Herrington, Ettienne du Plessis Atypical Archaean gold deposits Groves et al., 2003 Regional