Silver Swan, Black Swan, Cygnet

Western Australia, WA, Australia

Main commodities: Ni Cu
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The Black Swan operation is located within the Eastern Goldfields of Western Australia, ~43 km NNE of Kalgoorlie and lies within the Archaean Norseman-Wiluna greenstone belt of the Yilgarn Craton.   It comprises the high grade Silver Swan massive sulphide deposit, the high grade disseminated Cygnet ores and the Black Swan disseminated deposit (#Location: 30° 23' 27"S, 121° 38' 32"E).

The three deposits are hosted by the Black Swan Komatiite which lies within the upper greenschist to lower amphibolite facies metamorphosed, felsic-metasediment dominated, Gindalbie Formation. Within the project area, the Black Swan Komatiite dips steeply NE, is 150 to 600 m thick, and extends over a strike length of 3 km. Large volumes of the komatiite have been altered to carbonate-talc±quartz-sericite and it is only exposed over a very limited area. Where less altered, it is present as an antigorite-carbonate-talc±chrysotile serpentinite with relict coarse grained ortho-mesocumulate textures. The footwall is predominantly a thick sequence of acid-intermediate felsic volcanic rocks. Limited outcrop and drill data suggest the hangingwall sequence of the host komatiite is similar to that of the footwall. Both the Black Swan Komatiite and footwall sequence are intruded by felsic rocks similar in composition to the footwall felsic volcanics.

The Silver Swan deposit comprises a discrete, steeply plunging, high grade massive sulphide shoot composed of pyrrhotite, pentlandite, pyrite ± chalcopyrite, magnetite-ferrochromite mineralisation occurring on the footwall of the Black Swan Komatiite. It extends from a depth of 190 m, to past 740 m below the surface, with a 550 m down plunge extent, 20 m maximum thickness, strike length of 75 m, and dips at between 45 and 75°NE. The shoot comprises upper and lower lens like bodies, laterally separated by a poddy neck zone and has sharp. The overall lens has relatively undeformed contacts with wall rocks. The immediate hangingwall komatiitic rocks are devoid of network or disseminated sulphides, except where it overlaps with the Cygnet deposit. The footwall is more diffuse with small semi-rounded felsic clasts of the footwall volcanics persisting into the lower sections of the massive sulphides. Thin massive sulphide bands have been encountered within both the footwall and hangingwall of the main deposit. The massive sulphides are typically coarse-grained without and consistent compositional banding or layering, although they exhibit a 'lattice' texture of alternating stringers and subparallel lenses of pyrrhotite and pentlandite, with minor violarite, chalcopyrite, pyrite and gersdorffite.

Prior to mining, which commenced in 1997, the probable ore reserve at Silver Swan was 0.655 Mt @ 9.5% Ni. At December 2004, reported underground reserves and resources were: proved + probable ore reserves of 0.41 Mt @ 6.1% Ni (25 000 tonnes of contained nickel) plus indicated resources of 0.025 Mt @ 3.8% Ni (1000 tonnes of contained nickel).   At December 31, 2006, the remaining indicated + measured resource was 0.1 Mt @ 11.10% Ni, and the inferred resource was 0.070 Mt @ 10.80% Ni.

The Cygnet deposit occurs as a coherent, uniform lens of disseminated pyrite-millerite±vaesite ore, some 5 to 10 m stratigraphically above the base of the Black Swan Komatiite. It partially overlaps the Silver Swan deposit and has a strike length of 190 m, a maximum thickness of 40 m and a vertical extent of 300 m, although it persists with depth, but declines in thickness and grade. The ore zone is defined by the 0.75% Ni contour and dips at 70°NE. It has a high grade zone (averaging 2.5% Ni) in the footwall, decreasing in grade laterally outwards and stratigraphically upwards. Outside of the high grade interval, the zone averages 1% Ni. The gangue is coarsely crystalline interlocking plates of the iron bearing magnesite breunnarite with minor quartz with fine grained magnetite and occasional chromite.

In 1996, the Cygnet underground deposit was reported to contain 3.4 Mt @ 1.42% Ni, including a discrete zone of 0.93 Mt @ 2.47% Ni.   At December 31, 2006, the remaining indicated resource was 1.0 Mt @ 1.18% Ni (with no measured or inferred classification resources).

The Black Swan deposit is a low grade disseminated nickel accumulation some 400 m SE of Silver Swan and 50 m stratigraphically above the base of the Black Swan Komatiite. It has an elongate, 350 m long central core of disseminated pyrite-millerite-magnetite-violerite with a thickness of 130 m, surrounded by discrete, but smaller zones of mineralisation. The thickness and grade decreases with depth. Mineralisation comprises a dominant disseminated and a rare droplet style. The disseminated sulphides occur as <2 mm aggregates that are generally interstitial to the olivine pseudomorphs, while the droplets are up to 10 mm across. Both are predominantly pyrite with lesser millerite and magnetite, and minor violarite and chalcopyrite.

Prior to mining the Black Swan resource comprised 7 Mt @ 0.8% Ni, while in December 2004, the reported probable open pit ore reserve was 3.7 Mt @ 0.8% Ni (30 000 tonnes of contained nickel), plus an indicated resource of 3.3 Mt @ 0.8% Ni (26 400 tonnes of contained nickel).

Open pit mineral resources at December 31, 2006 were quoted by Norilsk Nickel as:
    Indicated + measured resource - 8.28 Mt @ 0.69% Ni
    Inferred resource - 1.69 Mt @ 0.68% Ni

The project is currently owned and operated by Norilsk Nickel.

The most recent source geological information used to prepare this summary was dated: 2001.    
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.

Silver Swan, Black Swan

  References & Additional Information
   Selected References:
Barnes S J,  2004 - Komatiites and nickel sulfide ores of the Black Swan area, Yilgarn Craton, Western Australia. 4. Platinum group element distribution in the ores, and genetic implications: in    Mineralium Deposita   v39 pp 752 - 765
Barnes S J, Wells M A and Verrall M R,  2009 - Effects of Magmatic Processes, Serpentinization, and Talc-Carbonate Alteration on Sulfide Mineralogy and Ore Textures in the Black Swan Disseminated Nickel Sulfide Deposit, Yilgarn Craton : in    Econ. Geol.   v104 pp 539-562
Barnes SJ , Hill RET and Evans NJ,  2004 - Komatiites and nickel sulfide ores of the Black Swan area, Yilgarn Craton, Western Australia. 3: Komatiite geochemistry, and implications for ore forming processes: in    Mineralium Deposita   v39 pp 729 - 751
Barnes SJ,  2004 - Introduction to nickel sulfide orebodies and komatiites of the Black Swan area, Yilgarn Craton, Western Australia: in    Mineralium Deposita   v39 pp 679 - 683
Dowling SE , Barnes SJ , Hill RET and Hicks JD,  2004 - Komatiites and nickel sulfide ores of the Black Swan area, Yilgarn Craton, Western Australia. 2: Geology and genesis of the orebodies: in    Mineralium Deposita   v39 pp 707 - 728
Hicks J D, Balfe G D  1998 - Silver Swan, Cygnet and Black Swan Nickel Deposit: in Berkman D A, Mackenzie D H (Eds),  Geology of Australian and Papua New Guinean Mineral Deposits The AusIMM, Melbourne    pp 339-346
Hill RET, Barnes SJ , Dowling SE and Thordarson T,  2004 - Komatiites and nickel sulphide orebodies of the Black Swan area, Yilgarn Craton, Western Australia. 1. Petrology and volcanology of host rocks: in    Mineralium Deposita   v39 pp 684 - 706
Marston R J, Groves D I, Hudson D R, Ross J R  1981 - Nickel sulfide deposits in Western Australia: a review: in    Econ. Geol.   v76 pp 1330-1363

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