Poseidon Nickel Ltd. acquired the Black Swan Operations assets in March 2015. The Poseidon is the 100% legal and beneficial owner of all Black Swan tenements.
The Black Swan tenements is registered to Poseidon Nickel Atlantis Operations Pty Ltd, a wholly owned subsidiary of Poseidon Nickel Ltd, following the purchase of the assets.
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Summary:
Mineralisation was first discovered in the Black Swan area during the nickel boom of the late 1960s. By 1972, drilling had defined a nickel sulphide resource, which is now recognised as the BSD orebody.
Nickel sulphide mineralisation at Black Swan is hosted by the Black Swan Komatiite Complex (BSKC), a 3.5 km long by 0.6 km thick arcuate lens of olivine cumulate and spinifex-textured komatiite flows. The complex is enclosed within a broad NE dipping sequence of intermediate felsic lavas and associated volcaniclastics. Graphitic black shales have been recognised within the enclosing felsic sequence, approximately 700 metres above and below the BSKC. The BSKC and enclosing felsic volcanic sequence face and dip steeply towards the NE. Except for several small areas of sub-outcrop, a thin veneer of lateritic red soil covers the BSKC.
The northern and southern tails of the BSKC thin and terminate rapidly in a complex series of interdigitating felsic and komatiite horizons. Where this occurs, the individual felsic horizons are typically of limited extent both along strike and down plunge. The southern tail of the complex is more pronounced and extends over approximately 1 km and is overlain by up to three discrete thin (spinifex textured) komatiite flows.
Large areas of the BSKC have been subjected to an intense carbonation event, which altered rocks of an earlier serpentinisation event to talc–carbonate ± quartz-sericite assemblages, and at the same time destroyed most primary igneous textures of the parent komatiite. Carbonate is by far the most dominant alteration mineral and is present as magnesite and siderite. Fine talc flakes, intergrown with the carbonate, form a significant component in some areas. Quartz is a minor constituent, replacing and enveloping the carbonate, while minor sericite is a widespread alteration product.
Two areas of serpentinite located near the centre and at the northern end of the BSKC survived the carbonation event. These serpentinite areas are dominated by antigorite ± carbonate-talc assemblages and typically exhibit well preserved igneous textures. The central serpentinite area is commonly referred to as the Black Swan serpentinite and is the host unit for most of the BSD mineralisation at surface.
Three principal nickel sulphide deposit types are recognised within the BSKC:
• High-grade (14% Ni) long (>1km) “ribbon-like” shoots of pyrrhotite-pentlandite-pyrite ± chalcopyrite massive sulphide mineralisation developed on the basal (western) contact of the complex of which Silver Swan and White Swan are the type examples.
• Low-grade (0.7-2.0% Ni) pyrite-millerite-vaesite-polydymite ± magnetite disseminated sulphide mineralisation developed internally within the complex of which Cygnet and the Black Swan deposits are the type examples; and
• Medium-grade (3.0-5.0%Ni) complex zones of massive, semi-massive and matrix mineralisation developed where the BSD sulphide rich flow contact internal felsic units within the Complex. Gosling and Golden Swan are the type examples of this type of deposit.
The mineral resource inventory available for a restart at BSO (for either a 1.1Mtpa smelter grade concentrate or 2.2Mtpa rougher concentrate option) is restricted to the unmined portions of the Silver Swan, Golden Swan and the BSD sulphide deposits.
Black Swan Disseminated (BSD) Sulphide Deposit
The BSD sulphide deposit is located 0.5km south of the Silver Swan portal. It forms part of the Cygnet-Black Swan disseminated sulphide horizon, a more-or-less continuous zone, comprising several disseminated sulphide horizons between mine grid 11800 mN and 11000 mN. Overlying the deposit is a zone of oxidised ultramafic, residual and transported ferruginised clays between 24 and 42 metres thick.
Near surface, the greater portion of the Black Swan resource is hosted by the Black Swan serpentinite. Talc– carbonate (magnesite and dolomite) altered rocks enclose the serpentinite to the north and south and at depth. Primary igneous textures comprising ortho- to mesocumulate textured olivine pseudomorphs between 1mm and 10mm in diameter are well preserved in the serpentinite. Igneous textures in the enclosing carbonate-altered rock types have generally been destroyed.
The BSD disseminated sulphide mineralisation forms between 2-10% of the host rock. They generally consist of composite grains of pyrite-millerite-magnetite±violarite in serpentinite areas with vaesite-polydymite becoming significant in the surrounding talc-carbonate altered rocks. Two textural sulphide types are recognised:
• Fine grained interstitial composite grains between olivine pseudomorphs; and
• Coarse grained blebby or droplet composites similar in size to the olivine pseudomorphs.
The fine-grained composites are more widely distributed, defining a broad, low grade mineralised horizon consisting of several discrete lenses. The coarser grained composites are much less widely distributed, forming small discrete, higher-grade zones within the sulphide rich lenses. They are also unique to the Black Swan deposit and are generally restricted to the disseminated sulphide lenses developed between 11200 mN and 11450 mN. The majority of the BSD sulphide mineralisation is contained within a central ‘main’ lens which is up to 50 metres thick and contains most of the coarser grained blebby sulphides.
Silver Swan Massive Sulphide Deposit The high-grade Silver Swan massive-sulphide nickel deposit consists of a series of discrete, steeply east dipping (70 - 90°) thin (<1 to 10 metres)short strike length lens-shaped shoots situated on the basal contact of the BSKC (see Figure 8). Individual shoots include Silver Swan, White Swan, Goose, Fledgling-Canard, Odette, Trumpeter, Peking Duck and Tundra Mute. This mineralisation plunges steeply towards the north along the southern flank of a substrate topographical high referred to as the Silver Swan footwall dome
Silver Swan massive sulphides are typically coarse grained without any consistent compositional layering. Two textural types are generally recognised. The more dominant ‘lattice’ or ‘trellis’ texture consists of alternating stringers and sub-parallel lenses of pentlandite and pyrrhotite with minor to trace amounts of violarite, chalcopyrite, pyrite and gersdorffite. Individual pentlandite lenses are typically 2 - 5 mm thick and several centimetres long and consist of 0.1 – 2 mm diameter granular pentlandite crystals. The pyrrhotite lenses consist of coarse granular aggregates of pyrrhotite with minor stringers and flames of pentlandite and pyrite. The other, less widely distributed textural type, is ‘leopard’ texture. It consists of coarse-grained circular pentlandite crystals (up to 10 mm in diameter) in a pyrrhotite matrix.
Golden Swan Semi-Massive Sulphide Deposit
The Golden Swan semi-massive nickel sulphide deposit is located within the BSKC, 450m south of the highgrade Silver Swan massive sulphide deposit (see Figure 9). The deposit, for which Mineral Resources have been estimated, consists of three contact (C10460, C10360 and C10300) and two hanging wall mineralised lenses (U10450 and U10370) (Figure 9). The contact lenses consist predominantly of pyrrhotite-pentlandite rich massive to semi-massive sulphide mineralisation intermixed in places with strong matrix-disseminated mineralisation. The lenses are developed on the contact between an underlying felsic volcanic re-entrant unit referred to as the Southern Terrace and the overlying mineralised BSD sulphide rich komatiite (host to the BSD sulphide deposit described above).
Within the overlying talc-carbonate altered Black Swan komatiite succession adjacent to the C10460 and C10360 contact lenses, pyrite-millerite rich disseminated and blebby sulphides are sufficiently developed to model the two hanging wall lenses U10450 and U10370.