Whim Creek Greenstone Belt - Whim Creek, Mons Cupri

Western Australia, WA, Australia

Main commodities: Cu Zn Pb Ag
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The Whim Creek, Salt Creek, Balla Balla and Mons Cupri VHMS copper-zinc-lead-silver-gold deposits are located adjacent to the Northwest Coastal Highway, mid-way between Karratha and Port Hedland in the Pilbara Region of Western Australia.

These depsoist are hosted by the 3010 to 2770 Ma Ma Whim Creek greenstone belt in the North Pilbara terrane of Western Australia. The Whim Creek greenstone belt contains a volcano-sedimentary succession that was deposited in two, separate meso-Archean basins, and crops out as a continuous arcuate belt some 85 km long and 5 to 10 km wide. The Liberty-Indee deposits, located 35 km to the south, occupies a volcanic horizon believed to be stratigraphically equivalent to the Whim Creek volcanics. Numerous other workings and geochemical and geophysical anomalies are evident in the belt.

The oldest lithostratigraphic unit (the Whim Creek Group) was deposited within an arc-related basin at ca. 3010 Ma.   It comprises early tholeiitic basalt lava of the Warambie Basalt, followed by felsic volcanism that produced large volumes of pyroclastic debris preserved as the Red Hill Volcanics.   Small- and large-volume dacite units were emplaced as syndepositional intrusions into the Red Hill Volcanics (Pike, et al., 2002).

The younger unit (the Bookingarra Group) was deposited in the >2950 Ma continental rift-related Mallina basin.   Sedimentation of the Bookingarra Group began with the deposition of reworked basement material derived from the Whim Creek Group.   Coarse-grained, volcanic sedimentary rocks grade upward into sandstone and shale derived from the weathering of a granite-dominated (continental) source. These are followed by up to a 2 km thickness of basaltic lava and high-level intrusions of the Mount Negri and Louden Volcanics (Pike, et al., 2002).

The two packages are separated by an erosional unconformity.   The Cistern Formation and Rushall Slate of the Bookingarra Group host the Whim Creek and Mons Cupri deposits respectively (Pike, et al., 2002).

Whim Creek is hosted by a 400 m thick sequence of essentially unmetamorphosed black slate, siltstone and minor sandstone beds which overlie rhyolite, breccia and tuffs, separated by a thin sand coarse conglomerate and breccia.   Ore occurs over strike length of 600 m in a single horizon that can be traced for 5000 m, and is developed 100 to 150 m above the volcanic-sediment contact.   The orebody is divided into two shoots in the cores of two gentle synforms separated by an anticlinal arch.   To the east and west the ore thins from 10 to 14 m down to 1.5 to 3.0 m (Reynolds, et al., 1975).   Overall, the mineralisation occurs as an ovoid lens (250 x 400 m) of stratabound Zn-Pb-Cu sulphides, underlain by stockworks, stringer and disseminated Cu-Zn mineralisation within a large pipe-like alteration zone (Venturex Resources, 2012).

Mineralisation comprises pyrite and/or pyrrhotite, chalcopyrite, sphalerite and minor galena.   Sulphides are zoned laterally with pyrite/pyrrhote and chalcopyrite in the thicker cores to pyrite and sphalerite on the thinning wings.   The upper boundary of the ore is sharp, while the lower is gradational and diffuse.   The orebody comprises an upper zone of finely banded, fine grained pyrite-sphalerite, a middle interval of massive, coarser grained pyrite/pyrrhotite-chalcopyrite and a lower zone of disseminated chalcopyrite.   Alteration includes sericite and Fe-carbonate associated with the laminated and massive ore, and chloritisation with the disseminated mineralisation (Reynolds, et al., 1975, Pike, et al., 2002).

Mons Cupri occurs within the Mons Cupri rhyolite fragmental which overlies an older extensive massive rhyolite.   The 600 m thick Mons Cupri rhyolite fragmental consists mostly of fragments of quartz-feldspar porphyry rhyolite within a fine grained felsic matrix, passing up from well stratified silty rocks at the base to a coarse angular fragmental at the top.   These are overlain by the 22 m thick Cistern Formation, interpreted to be largely a massive, gritty welded aggregate of quartz and feldspar crystals.   This is in turn overlain by the 150 m thick Whim Creek Slate, with intercalated andesites and felsic volcanics.

Mineralisation occurs as a round hill 200 m in diameter and 90 m tall of oxidised low grade ore.   The orebody comprises two zones:
1). A lower chalcedony-chlorite-siderite zone which strikes east-west, is 1100 m long, 250 m wide at the top, thinning downwards to 25 m wide at depth and contains the bulk of the Cu ore.   Mineralisation is characterised by a series of anastomosing chalcopyrite bearing chalcedonic veins 1 to 10 cm wide which parallel the dip of the ore zone and by disseminated chalcopyrite within the adjacent chloritised hosts.   The chalcopyrite content increases upwards towards the conformable, siliceous Cu-Pb-Zn-Ag ore, just below which a 35 m thick zone of high grade (2 to 4% Cu) occurs.
2). An upper siliceous, layered conformable band of copper-lead-zinc-silver ore as coarse grained pyrite, chalcopyrite, galena, sphalerite, tetrahedrite and trace bournonite and linnaeite.   The underlying crosscutting chlorite-copper zone widens to 270 m near the contact with the slate/Cistern Formation boundary where a thinly layered, 3 to 15 m thick sequence of tuff, fragmental and chert with lateral dimensions of 270 x 400 m contains massive chalcopyrite, galena, sphalerite, pyrite and silver.   Grades are lower in the thicker part of the ore band (eg, 1.2% Cu, 5.2% Pb, 6.5% Zn, 62 g/t Ag), while in the thinner sections it may assay 0.5% Cu, 10.9% Pb, 16.2% Zn, 171 g/t Ag.   This ore zone is limited upwards by the overlying slate.

Salt Creek is the largest known VHMS deposit in the Salt Creek Belt, approximately 17 km north of Whim Creek, comprising a pair of south-east plunging ribbon-like shoots of zinc and copper-zinc massive sulphides.

The Balla Balla VHMS massive sulphide lens lies 6 km east of the Salt Creek occurrence, and is interpreted to lie within the same host unit as Salt Creek. It comprises a steeply south-dipping, massive zinc-lead sulphide lens over a strike length of >400 m with a vertical extent of >200 m containing some copper sulphide rich mineralisation within the horizon that varies from 3 to 10 m in thickness with grades of 2.5 to 12.5% Zn, 0.1 to 3.6% Cu and 0.65 to 2.4% Pb.

At Whim Creek - total production to 1924 was 0.076 Mt @ 13.2% Cu.
    Resources in 1975 were 0.132 Mt @ 4.8% Cu, and 0.295 Mt @ 2.5% Cu (Reynolds, et al., 1975).
    Resource in 1987 were 1 Mt @ 1.6% Cu, 1.3% Zn, 0.2% Pb (Barley, 1995).
    Indicated + inferred resource in 2011 were 0.97 Mt @ 1.4% Cu, 1.2% Zn, 0.2% Pb. 8.8 g/t Ag, 0.1 g/t Au Venturex Resources, 2012).
    Probable reserve in 2011 were 0.687 Mt @ 1.7% Cu, 1.1% Zn, 0.2% Pb. 8.9 g/t Ag, 0.1 g/t Au Venturex Resources, 2012).

At Mons Cupri - resources in 1975 were:
    Copper orebody - 12 to 15 Mt @ 1% Cu, and,
    Stratabound orebody -1 Mt @ 2.5% Pb, 3.6% Zn, 62 g/t Ag.
    Measured + indicated + inferred resource in 2011 were 4.607 Mt @ 0.9% Cu, 1.3% Zn, 0.5% Pb. 24.1 g/t Ag, 0.1 g/t Au
        Venturex Resources, 2012).
    Probable reserve in 2011 were 2.815 Mt @ 1.7% Cu, 1.8% Zn, 0.8% Pb. 32.1 g/t Ag, 0.2 g/t Au Venturex Resources, 2012).

At Salt Creek - resources and reserves in 2011 were:
    Measured + indicated + inferred resource - 1.003 Mt @ 2% Cu, 7% Zn, 2.1% Pb. 52.0 g/t Ag, 0.3 g/t Au Venturex Resources, 2012).
    Probable reserve in 2011 were 0.597 Mt @ 1.8% Cu, 6.6% Zn, 2.1% Pb. 53.1 g/t Ag, 0.3 g/t Au Venturex Resources, 2012).

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2002.    
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.

  References & Additional Information
   Selected References:
Barley M E  1995 - Archaean volcanic-hosted base metal sulphide mineralisation in Western Australia: in    Australian Institute of Geoscientists   Bull 16 pp 41-50
Bishop J R, Lewis R J G  1992 - Geophysical signatures of Australian volcanic-hosted massive sulfide deposits: in    Econ. Geol.   v87 pp 913-930
Huston D L,  2006 - Mineralization and regional alteration at the Mons Cupri stratiform Cu-Zn-Pb deposit, Pilbara Craton, Western Australia: in    Mineralium Deposita   v41 pp 17-32
Large R R  1992 - Australian volcanic-hosted massive sulfide deposits: features, styles, and genetic models: in    Econ. Geol.   v87 pp 471-510
Miller L J, Gair H S  1975 - Mons Cupri copper-lead-zinc-silver deposit: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 5 pp 195-202
Pike G, Cas R, Smithies R H  2002 - Geological constraints on base metal mineralization of the Whim Creek Greenstone Belt, Pilbara Craton, Western Australia: in    Econ. Geol.   v97 pp 827-845

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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