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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).

Nickel mineralisation was first discovered in the Black Swan area during the nickel boom of the late 1960s and by 1972, Australian Anglo American Limited had outlined a small nickel sulphide resource in what is now known as the Black Swan Disseminated orebody, but no further work was undertaken and the leases relinquished. The prospect was not given and further significant exploration attention until 1995 when tenements were acquired by a joint venture between MPI Mines Limited and Outokumpu Exploration Ventures Pty Limited. Exploration drilling intersected the Silver Swan Massive sulphide deposit in the second drill hole. During the next two years the White Swan, Cygnet and Gosling deposits were discovered and evaluated. Construction commenced in 1996 and by May 1997 the first underground ore was brought to the surface. Excavation at the Black Swan open pit commenced in February 2004 and the first ore was mined from the pit in May 2004. In November 2004, LionOre Australia (Nickel) Limited took control of the operation through the acquisition of MPI Mines. In 2007, LionOre was acquired by the Norilsk Nickel Group of companies. The Silver Swan underground mine, the Black Swan open pit and the processing plant were placed into care and maintenance in February 2009 by Norilsk as a result of low nickel prices. Poseidon Nickel subsequently purchased the operation from Norilsk in late 2014 with a view to restarting mining activities (Poseidon Nickel website, viewed 2020)

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 3.5 km. The northern and southern tails of the complex thin and terminate rapidly in a complex series of interdigitating felsic and komatiite horizons. The Black Swan Complex contains two major phases of Kambalda style mineralisation. The first was a series of thin komatiite flows at the base which formed the Silver Swan massive sulphide mineralisation. Subsequent, a much thicker flow formed above, hosting the Black Swan disseminated mineralisation. 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 Ore Reserves and Mineral Resources were:
  Proved + Probable Ore Reserves - 0.41 Mt @ 6.1% Ni (25 000 tonnes of contained nickel) plus
  Indicated Mineral Resources - 0.025 Mt @ 3.8% Ni (1000 tonnes of contained nickel).
At December 31, 2006, the remaining Indicated + Measured Mineral Resource was 0.1 Mt @ 11.10% Ni, plus
  Inferred Resource - 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 Mineral 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 Mineral 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 Mineral Resource - 8.28 Mt @ 0.69% Ni
    Inferred Mineral Resource - 1.69 Mt @ 0.68% Ni

The remaining Mineral Resources at the Black Swan operation at 30 June, 2019 (Poseidon Nickel Limited Annual Report, 2019) were:
  Black Swan open pit, Indicated + Inferred Resources - 30.70 Mt @ 0.58% Ni, 0.01% Co at 0.4% Ni cutoff;
  Silver Swan underground, Indicated + Inferred Resources - 0.168 Mt @ 9.5% Ni, 0.19% Co, 0.4% Cu at 4.5% Ni cutoff.

The most recent source geological information used to prepare this decription 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   v.39, pp. 752 - 765.
Barnes, S.J.,  2004 - Introduction to nickel sulfide orebodies and komatiites of the Black Swan area, Yilgarn Craton, Western Australia: in    Mineralium Deposita   v.39, pp. 679 - 683.
Barnes, S.J., Hill, R.E.T. and Evans, N.J.,  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   v.39, pp. 729 - 751.
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.   v.104, pp. 539-562.
Dowling, S.E., Barnes, S.J., Hill, R.E.T. and Hicks, J.D.,  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   v.39, 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, R.E.T., Barnes, S.J., Dowling, S.E. 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   v.39, pp. 684 - 706.
Marston, R.J., Groves, D.I., Hudson, D.R. and Ross, J.R.,  1981 - Nickel sulfide deposits in Western Australia: a review: in    Econ. Geol.   v.76, pp. 1330-1363.

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, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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