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Scotia |
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Western Australia, WA, Australia |
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Ni Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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Scotia was a small komatiite hosted massive sulphide Fe-Ni-Cu deposit located some 65 km north of Kalgoorlie in Western Australia.
The deposit was discovered in 1968 and mined from October 1969 until cessation of operations in September 1977 due to a major underground collapse.
The Scotia deposit is hosted by mafic and ultramafic rocks that are part of a continuous belt striking NNW from Kalgoorlie and Kambalda. These greenstones, which belong to the 2715 to 2690 Ma Kambalda Sequence, are typically tightly folded with NNW axes and are metamorphosed to lower greenschist facies. The orebody and host sequence dips steeply west and it is considered to form the Eastern limb of a south plunging syncline. Granite outcrops in the core of the adjacent anticline immediately to the east.
The succession in the deposit area comprises a lower low-Mg tholeiitic basaltic unit that is ~500 m thick, with intercalated tuffs, thin sedimentary rocks and some pods of high Mg basalt and gabbro. The basalts comprise ~65% amphibole (either hornblende or actinolite); 20% plagioclase; 10% quartz, 3% chlorite and 2% opaques. Approximately 5 to 15 m of black graphitic slates with minor pyrite and quartz-biotite schists separate the basalts from the overlying ultramafic suite. The schists are interpreted to be of epiclastic volcano-sediments with an andesitic composition. The ultramafic suite is up to 600 m thick and comprises numerous discrete lenses of peridotitic rock intercalated with thin discontinuous lenses of metasedimentary rocks. The ultramafic rocks are composed of olivine, serpentine (replacing olivine) amphibole, chlorite and minor calcite and host the mineralisation. The ultramafics are overlain by a further 600 m of sedimentary rocks.
In the immediate deposit area, the sedimentary unit is separated from the lower sections of the ultramafic by a chlorite shear zone up to 15 cm thick. Adjacent to be contact with the overlying ultramafic rocks, the sedimentary unit has been bleached and silicified in many places. The ore bearing ultramafic is a single lens-shaped dunitic/komatiite unit ~500 m long and up to 50 m wide that extends from the surface to a depth of at least 450 m and occurs at the base of the ultramafic suite. It strikes NNW and dips steeply west. The orebody occurs in its central sections, in an embayment of its footwall into the underlying sedimentary rocks, and has a strike length of 150 m, thickness of up to 20 m and down plunge extent of 370 m.
The sulphide orebody comprises a basal massive sulphide, progressively overlain by network and disseminated sulphides and then a barren zone, which is, in turn followed by an altered zone and the overlying ultramafic suite. The upper alteration zone ranges from a few cm to 5 m thick and occurs in highly metamorphosed and metasomatised sedimentary rocks and mafic volcanics. The orebody contains ~10% sulphides and has an estimated average grade of 3.07% Ni, 0.25% Cu at a cut-off of 1% Ni. The discontinuous basal massive sulphides, where present, are up to 2 m thick and contain 15 to 20% Ni, whilst the overlying up to 20 m of network and disseminated ore carries 1 to 7% Ni. The ore contains pentlandite, violarite, pyrrhotite, pyrite and minor valeriite, chalcopyrite, magnetite and Cr spinel. The present sulphide mineralisation is not the original, and was released during the serpentinisation of the olivine. The serpentinised host has well preserved olivine crystals at its core, with inclusions of pentlandite and magnetite.
Production to 1977 was 1.4 Mt @ 2.2% Ni.
Remaining reserves in 1981 were 0.82 Mt @ 2.14% Ni.
For more detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1981.
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.
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Christie D 1975 - Scotia Nickel Sulphide deposit: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne Mono 5 pp 121-125
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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.
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Page M L, Schmulian M L 1981 - The proximal volcanic environment of the Scotia nickel deposit: in Econ. Geol. v76 pp1469-1479
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Stolz G W, Nesbitt R W 1981 - The Komatiite nickel sulfide association at Scotia: a petrochemical investigation of the ore environment: in Econ. Geol. v76 pp 1480-1502
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