Olympic Dam

South Australia, SA, Australia

Main commodities: Cu U Au
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The Olympic Dam copper-gold-uranium-REE ore deposit is located some 550 km NNW of Adelaide and 275 km NNW of Port Augusta, in northern South Australia (#Location: 30° 26' 24"S, 136° 53' 22"E).

Olympic Dam and all of the other significant known IOCG mineralised systems of the Mesoarchaean to Mesoproterozoic Gawler Craton are hosted within Palaeo- to Mesoproterozoic rocks, and are distributed along the eastern rim of the currently preserved craton to define the Olympic IOCG Province (Skirrow et al., 2007).   Olympic Dam lies below the Neoproterozoic Stuart Shelf, where >300 m of flat lying, barren, Neoproterozoic to lower Palaeozoic sedimentary rocks unconformably overlie both the craton and the ore deposit. Some 75 km to the east, this cover sequence expands over the major NNW trending Torrens Hinge Zone at the edge of the craton, into the thick succession of the north-south aligned Neoproterozoic Adelaide Geosyncline rift basin, that masks the mid- to late-Palaeoproterozoic suture between the Gawler craton and Palaeo- to Mesoproterozoic Curnamona Province to the east.

The oldest basement rocks in the Gawler craton are Meso- to Neoarchaean gneisses (to the west) and metasedimentary and meta-volcanosedimentary rocks, and deformed granites correlated with the Palaeoproterozoic 1.96 to 1.85 Ga Hutchison Group, the 1.79 to 1.74 Ga Wallaroo Group, and the 1.85 to 1.69 Ga Lincoln Complex (Donington Suite) granitoids, respectively. These rocks are intruded by the widespread Mesoproterozoic A- and I-type granitoids of the ~1.59 Ga Hiltaba Suite (with the former dominating in the Olympic IOCG Province) and are overlain by comagmatic bimodal volcanic rocks of the areally extensive Gawler Range Volcanics (GRV).

Mineralisation at Olympic Dam is hosted by the 50 km2 Olympic Dam Breccia Complex (ODBC) that is developed within the Mesoproterozoic (1600 to 1585 Ma) Roxby Downs Granite. The Roxby Downs Granite is a pink to red coloured, undeformed, unmetamorphosed, coarse to medium grained, quartz-poor syenogranite with A-type affinities that is petrologically and petrochemically similar to granitoids of the Hiltaba Suite. Other lithologies within the ODBC comprise a variety of granite- to hematite-rich breccias, sedimentary facies, felsic/mafic/ultramafic dykes, volcaniclastic units, basalts and their altered/mineralised equivalents. The ODBC and the surrounding Roxby Downs Granite form a local basement high on a broader regional basement uplift.

Within the overall alteration envelope, the distribution of mineralisation and alteration exhibits a downward and outward zonation, while the ODBC correspondingly comprises a downward narrowing, funnel-shaped body of fractured, brecciated and hydrothermally altered granite which has resulted in a great variety of granitic, hematitic and siliceous breccias. The complex has a conical, downward tapering, central "core" of barren, but intensely altered hematite-quartz-breccia, passing outwards through concentrically zoned breccia types, including heterolithic hematite breccias (with clasts dominantly of granite and recycled hematite breccias, and domains where abundant sedimentary and volcaniclastics rocks predominate locally), to monoclastic granite breccias with a magnetite/hematite matrix, to weak incipient microfracturing of the RDG on the outer margins. A halo of weakly altered and brecciated granite extends out approximately 5 to 7 km from the core in all directions to an indistinct and gradational margin with the host granite. This progression represents an outward decrease in the degree of brecciation and intensity of iron metasomatism away from the core of the complex. The quantity of recycled hematite breccia, GRV and sedimentary rock clasts within the heterolithic hematite breccias decreases from shallow to deep levels (Ehrig, 2010; McPhie et al., 2010). The areal extent of more intensely hematite altered breccias within the complex is >5 km in a NW-SE direction, up to 3 km across, and is known to extend to a depth of at least 1400 m.

The development of the ODBC, which shows textural evidence of polycyclic alteration and brecciation events, can be considered as having formed by the progressive hydrothermal brecciation and iron metasomatism of the host granite. In detail, alteration assemblages are highly variable with complex mineral distribution patterns resulting from the polycyclic nature of the hydrothermal activity. Never-the-less, there are systematic patterns of alteration that are recognised across the deposit as a whole, and at the scale of individual breccia zones, with the degree of alteration intensity being directly related to the amount of brecciation.

The bulk of the mineralisation within the Olympic Dam deposit is associated with an assemblage of hematite-sericite-fluorite-barite-chalcopyrite-bornite-chalcocite (djurleite), the outer margin of which largely corresponds to the limits of the ODBC, where a deeper magnetite-carbonate-chlorite-pyrite±chalcopyrite zone marks the transition to the more regional magnetite-K feldspar±actinolite±carbonate assemblage (Ehrig, 2010). No associated sodic metasomatism has been observed.

The better mineralisation and strongest alteration outside of the barren core corresponds to the best-developed hematite-granite breccias. The concentric, moderate to steeply inward dipping breccia zones of the ODBC are cut by a convoluted, but overall roughly horizontal, ~50 m thick layer characterised by chalcocite and bornite, ~100 to 200 m below the unconformity with the overlying Neoproterozoic cover sequence. Both the upper and lower margins of this zone are mappable. Above the upper margin, sulphides are rare and little copper mineralisation is found in the same hematitic breccias. The lower margin marks a rapid transition to chalcopyrite, which decreases in copper grade downwards, corresponding to an increase in the pyrite:chalcopyrite ratio. While this zone is largely horizontal, as it approaches the central barren core it steepens markedly, but is still evident at depths of >1 km below the Neoproterozoic unconformity (Reeve et al., 1990; Reynolds, 2000; Ehrig, 2010). The geometry of this mineral zonation, strongly suggest interaction between upwelling and downward percolating fluids. For all fluids related to hematite alteration, fluid inclusion homogenisation temperatures are mostly between 150 and 300°C and salinities range from ~1 to ~23% NaCl equiv. (Knutson et al., 1992; Oreskes and Einaudi, 1992; Bastrakov et al., 2007).

The higher grade underground resource occurs as up to 150 separate bodies distributed within an annular zone up to 4 km in diameter surrounding the central barren hematite-quartz breccia. These bodies correspond to the overlap of the flat-lying chalcocite-bornite layer and the steeper, inwardly dipping ring of hematite-granite breccias.

The principal copper-bearing minerals are chalcopyrite, bornite, chalcocite (djurleite-digenite), which on the basis of Nd isotopic data, textural and geochemical features appear to have precipitated cogenetically. Minor native copper and other copper-bearing minerals are locally observed. The main uranium mineral is uraninite (pitchblende), with lesser coffinite and brannerite. Minor gold and silver is intimately associated with the copper sulphides. The main REE-bearing mineral is bastnaesite. Copper ore minerals occur as disseminated grains, veinlets and fragments within the breccia zones. Massive ore is rare.

At the end of 1989, after commencing mining operations in mid-1988, reported resources and reserves (Reeve et al., 1990) amounted to:
    Measured + indicated resource = 450 Mt @ 2.5% Cu, 0.6 g/t Au, 6.0 g/t Ag, 0.8 kg/tonne U
    Inferred resource = 2000 Mt @ 1.6% Cu, 0.6 g/t Au, 3.5 g/t Ag, 0.6 kg/tonne U
    Proved reserve = 13 Mt @ 3.0% Cu, 0.3 g/t Au, 10.2 g/t Ag, 1.1 kg/tonne U
    Proved gold reserve = 2.3 Mt @ 1.6% Cu, 3.6 g/t Au, 2.9 g/t Ag, 0.3 kg/tonne U

At December 2004, published (BHP Billiton, 2005) reserves and resources were:
    Proved+probable reserves totalled 761 Mt @ 1.5% Cu, 0.5 g/t Au, 0.5 kg/tonne U
    within a total resource of   3810 Mt @ 1.1% Cu, 0.5 g/t Au, 0.4 kg/tonne U

At 30 June 2012, the published resources (BHP Billiton, September, 2012) amounted to:
    Measured resource = 1474 Mt @ 1.03% Cu, 0.35 g/t Au, 1.95 g/t Ag, 0.30 kg/tonne U
    Indicated resource = 4843 Mt @ 0.84% Cu, 0.34 g/t Au, 1.50 g/t Ag, 0.27 kg/tonne U
    Inferred resource = 3259 Mt @ 0.70% Cu, 0.25 g/t Au, 0.98 g/t Ag, 0.23 kg/tonne U
    Total resource = 9576 Mt @ 0.82% Cu, 0.31 g/t Au, 1.39 g/t Ag, 0.26 kg/tonne U
This resource includes a total proved + probable reserve of:
    629 Mt @ 1.76% Cu, 0.73 g/t Au, 3.36 g/t Ag, 0.57 kg/tonne U
At the same date, the separate non-sulphide gold resource was 364 Mt @ 0.75 g/t Au, comprising:
    Measured resource = 73 Mt @ 0.85 g/t Au;   Indicated resource = 255 Mt @ 0.73 g/t Au;   Inferred resource = 36 Mt @ 0.70 g/t Au.

At 30 June 2015, the published resources (BHP Billiton Annual Report, 2015) amounted to:
    Measured resource = 1.330 Gt @ 0.96% Cu, 0.40 g/t Au, 2.0 g/t Ag, 0.29 kg/tonne U
    Indicated resource = 4.610 Gt @ 0.79% Cu, 0.32 g/t Au, 1.0 g/t Ag, 0.24 kg/tonne U
    Inferred resource = 4.120 Gt @ 0.71% Cu, 0.24 g/t Au, 1.0 g/t Ag, 0.25 kg/tonne U
    Total resource = 10.060 Gt @ 0.78% Cu, 0.30 g/t Au, 1.0 g/t Ag, 0.25 kg/tonne U
This resource includes a total proved + probable reserve of:
    484 Mt @ 1.95% Cu, 0.74 g/t Au, 4.0 g/t Ag, 0.59 kg/tonne U
    Stockpile - 44 Mt @ 0.99% Cu, 0.51 g/t Au, 2.0 g/t Ag, 0.37 kg/tonne U
At 30 June 2015, a separate non-sulphide gold resource was 283 Mt @ 0.84 g/t Au, which was not reported in 2015.

Production in 2011-12 totalled 192 600 tonnes of Cu, 3.66 t Au, 28.21 t Ag, 3885 tonnes U
Production in 2014-15 totalled 124 500 tonnes of Cu, 3.26 t Au, 22.52 t Ag, 3144 tonnes U

The mine is owned and operated by a subsidiary of BHP Billiton Ltd.

The most recent source geological information used to prepare this summary was dated: 2012.     Record last updated: 30/8/2012
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

Olympic Dam

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Belpario A and Freeman H  2004 - Common geological characteristics of Prominent Hill and Olympic Dam - Implications for iron oxide copper-gold exploration models : in   Hi Tech and World Competitive Mineral Success Stories Around the Pacific Rim,  Proc. Pacrim 2004 Conference, Adelaide, 19-22 September, 2004, AusIMM, Melbourne    pp 115-125
Drummond B, Lyons P, Goleby B and Jones J,  2006 - Constraining models of the tectonic setting of the giant Olympic Dam iron oxide-copper-gold deposit, South Australia, using deep seismic reflection data: in    Tectonophysics   v420 pp 91-103
Ehrig K,  2010 - Olympic Dam: 35 years since discovery, 2.3 million metres of diamond core and new ideas - Abstract: in   Giant Ore Deposits Down Under 13th Quadrennial IAGOD Symposium, Adelaide, South Australia, 6-9 April, 2010,   Symposium Proceedings, pp. 9-10
Ehrig, K., McPhie, J. and Kamenetsky, V.,  2012 - Geology and Mineralogical Zonation of the Olympic Dam Iron Oxide Cu-U-Au-Ag Deposit, South Australia: in Hedenquist J W, Harris M and Camus F, 2012 Geology and Genesis of Major Copper Deposits and Districts of the World - A tribute to Richard H Sillitoe, Society of Economic Geologists   Special Publication 16, pp. 237–267
Ferris G M, Schwartz M P and Heithersay P  2002 - The geological framework, distribution and controls of Fe-Oxide Cu-Au mineralisation in the Gawler Craton, South Australia: Part 1 - Geological and tectonic framework: in Porter T M 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v2 pp 9-31
Haynes D W,  2000 - Iron Oxide Copper (-Gold) Deposits: Their Position in the Ore Deposit Spectrum and Modes of Origin: in Porter T M (Ed), 2000 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.1 pp. 71-90
Haynes D W, Cross K C, Bills R T, Reed M H  1995 - Olympic Dam ore genesis: a fluid mixing model: in     Econ. Geol.   v90 pp 281-307
Hayward N and Skirrow R,  2010 - Geodynamic Setting and Controls on Iron Oxide Cu-Au (±U) Ore in the Gawler Craton, South Australia: in Porter T M, (Ed),  2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.3 pp. 119-146
Heinson G S, Direen N G and Gill R G,  2006 - Magnetotelluric evidence for a deep-crustal mineralizing system beneath the Olympic Dam iron oxide copper-gold deposit, southern Australia: in    Geology   v34 pp 573–576
Hitzman M W and Valenta R K,  2005 - Uranium in iron oxide-copper-gold (IOCG) systems: in    Econ. Geol.   v100 pp 1657-1661
Johnson J P, Cross K C  1995 - U-Pb geochronological constraints on the genesis of the Olympic Dam Cu-U-Au-Ag deposit, South Australia: in    Econ. Geol.   v.90 pp 1046-1063
Knutson J, Donnelly T H, Eadington P J and Tonkin D G,  1992 - Hydrothermal alteration of middle Proterozoic basalts, Stuart Shelf, South Australia; a possible source for Cu mineralization : in    Econ. Geol.   v.87 pp. 1054-1077
Mauger, A.J., Ehrig, K., Kontonikas-Charos, A., Ciobanu, C.L., Cook, N.J. and Kamenetsky, V.S.,  2016 - Alteration at the Olympic Dam IOCG–U deposit: insights into distal to proximal feldspar and phyllosilicate chemistry from infrared reflectance spectroscopy: in    Australian J. of Earth Sciences   v.63, pp. 959-97.
McPhie J, Kamenetsky V, Allen S, Ehrig K, Agangi A and Bath A,  2011 - The fluorine link between a supergiant ore deposit and a silicic large igneous province: in    Geology   v.39 pp. 1003-1006
McPhie J, Kamenetsky V, Chambefort I, Ehrig K and Green N,  2010 - The origin of Olympic Dam: A revolutionary new view - Abstract: in   Giant Ore Deposits Down Under 13th Quadrennial IAGOD Symposium, Adelaide, South Australia, 6-9 April, 2010,    Symposium Proceedings, pp. 76-77
McPhie J, Kamenetsky V, Chambefort I, Ehrig K and Green N,  2011 - Origin of the supergiant Olympic Dam Cu-U-Au-Ag deposit, South Australia: Was a sedimentary basin involved ?: in    Geology   v.39 pp. 795-798
Oreskes N and Hitzman M W,  1993 - A model for the origin of Olympic Dam-type deposits: in Kirkham R V, Sinclair W D, Thorpe R I, Duke J M, (Eds) 1993  Mineral Deposit Modelling Geological Association of Canada   Special Paper 40 pp. 615-633
Oreskes N, Einaudi M T  1990 - Origin of rare earth element-enriched Hematite breccias at the Olympic Dam Cu-U-Au-Ag deposit, Roxby Downs, South Australia: in    Econ. Geol.   v85 pp 1-28
Oreskes N, Einaudi M T  1992 - Origin of hydrothermal fluids at Olympic Dam: preliminary results from fluid inclusions and stable isotopes: in    Econ. Geol.   v87 pp 64-90
Reeve J S, Cross K C, Smith R N, Oreskes N  1990 - Olympic Dam copper-uranium-gold-silver deposit: in Hughes F E (Ed),  Geology of the Mineral Deposits of Australia and Papua New Guinea The AusIMM, Melbourne   v2 pp 1009-1035.
Reynolds L J  2000 - Geology of the Olympic Dam Cu-U-Au-Ag-REE deposit: in Porter T M (Ed), 2000 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective PGC Publishing, Adelaide   v1 pp. 93-104
Skirrow R G, Bastrakov E, Raymond O L, Davidson G and Heithersay P,  2002 - The geological framework, distribution and controls of Fe-Oxide Cu-Au mineralisation in the Gawler Craton, South Australia: Part 2 - Alteration and mineralisation: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide   v2 pp 33-47
Smith R J,  2002 - Geophysics of Iron Oxide Copper-Gold Deposits: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide   v.2 pp. 357-367
Smith R N  1993 - Olympic Dam: some developments in geological understanding over nearly two decades: in   The AusIMM Centenary Conference, Adelaide, 30 March-4 April, 1993 AusIMM Publication Series 2/93    pp 113-118
Tappert, M.C., Rivard, B., Giles, D., Tappert, R. and Mauger, A.,  2013 - The mineral chemistry, near-infrared, and mid-infrared reflectance spectroscopy of phengite from the Olympic Dam IOCG deposit, South Australia: in    Ore Geology Reviews   v.53, pp. 26-38,
Widdup H, Fouet T, Hodgkison J, McCuaig T C and Miller J  2004 - A three dimensional structural interpretation of the Olympic Dam deposit - Implications for mine planning and exploration: in   Hi Tech and World Competitive Mineral Success Stories Around the Pacific Rim,  Proc. Pacrim 2004 Conference, Adelaide, 19-22 September, 2004, AusIMM, Melbourne    pp 417-426
Williams P J, Barton M D, Johnson D A, Fontbote L, de Haller A, Mark G, Oliver N H S and Marschik R,  2005 - Iron oxide copper-gold deposits: Geology, space-time distribution and possible modes of origin: in Hedenquist J W, Thompson J F H, Goldfarb R J and Richards J P (Eds.), 2005 Economic Geology 100th Anniversary Volume, Society of Economic Geologists, Denver,    pp 371-405
Williams, P.J. and Pollard, P.J.,  2003 - Australian Proterozoic Iron Oxide-Cu-Au Deposits: An Overview with New Metallogenic and Exploration Data from the Cloncurry District, Northwest Queensland: in    Exploration & Mining Geology, CIM   v.10, No. 3, pp. 191-213.

 References to this deposit in PGC Publications: Want any of our books ? Pricelist
Reynolds L, 2000 - Geology of the Olympic Dam Cu-U-Au-Ag-REE Deposit,   in  Porter T M, (Ed.),  Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective,  v1  pp 93-104
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