Scotia Nickel Mine, Bardoc, Broad Arrow Goldfield, Kalgoorlie-Boulder Shire, Western Australia, Australiai

Regional Level Types
Scotia Nickel Mine	Mine
Bardoc	- not defined -
Broad Arrow Goldfield	Ore Field
Kalgoorlie-Boulder Shire	Shire
Western Australia	State
Australia	Country

The Scotia Nickel deposit was discovered around 1968 by John Jones, self-trained in geology, and a pastoralist from the nearby Hampton Hill Station. He went onto become general manager of the mine. It was an underground operation, ceasing in 1977 after a major underground collapse. During this time it produced 1.4 million tonnes of ore at 2.2% grade Ni. It is a small komatiite hosted massive sulphide Fe-Ni-Cu deposit 65 kilometres north of Kalgoorlie. It is just north of Broad Arrow, on the eastern side of the Goldfields Highway, and 15 kilometres further north are the related the St Patricks and St Andrews nickel prospects.

The area contains a lower sequence of mafic rocks, separated by andesitic sediments from an upper sequence of ultramafic komatiites, intruded by tonalitic granitoids. The mafic sequence is dominated by tholeiitic Mg basalts, minor horizons of peridotite, high Mg basalt, gabbro and low Mg basalt. The andesitic sediment at the lower boundary of the ultramafic sequence hosts the nickel sulphide, and was eroded from a nearby calc-alkaline volcanic centre.

The ore bodies are ultramafic lenses showing well preserved olivine crystals at its core. with pentlandite and magnetite inclusions. The basal and middle units of the matrix ore are overlain with disseminated mineralisation, and the upper unit is solely disseminated mineralisation. The ore shows pentlandite, violarite, pyrrhotite, pyrite and minor valeriite, magnetite and Cr spinel. The present sulphide mineralisation is not the original, and was released during the serpentinisation of the olivine. One reference states: 'the ore unit was emplaced by a mush of olivine crystals, lubricated by an immiscible sulphide oxide melt in close proximity to its magma conduit or vent'.

St Patricks and St Andrew deposits are 600 metres apart with the former in two parallel structurally controlled zones and the latter within several parallel zones, both in the Eastern Contact Trend. These prospects were discovered in 2007.

In 1975, garnierite was reported from the mine. While a relatively common material, it is noted at only three other locations on Mindat in Western Australia. Considering the State is rich in nickel, one would expect it to be more common.

Three garnierite specimens were sampled from the waste heap after the excavation of a ventilation shaft and studied in detail (Nickel & Bridge, 1975). It occurred 15-23 metres below the surface in the oxidised zone with other secondary nickel species. The three specimens were: 1) discontinuous surface coatings on limonitic serpentinite 2) quartz-garnierite intergrowths in a silicified ferruginous gossan 3) soft patches in a vein of nickeloan magnesite containing serpentinite fragments and coated with small quartz crystals. The garnierite on these specimens was bright green. It was all determined to be a high-nickel talc-like mixed-layered hydrous silicate.

Glaukosphaerite occurs as films overgrown with quartz crystals on an antigorite-talc-goethite rock.

At Scotia, linnaeite occurs as disseminations in graphitic shale and biotite schists, as irregular veinlets filling fractures and shears, and as isolated grains in schist. It is found in combination with mackinawite, valleriite, chalcopyrite, covelline, nickeliferous gel pyrite, and violarite, as supergene alteration. The linnaeite is creamy white contrasting with the golden-brown mackinawite.

Normal violarite and the cupriferous variety has developed as lamellae at the interfaces with gel pyrite. Cupriferous violarite has locally crystallised into larger areas, but is optically indistinguishable from normal violarite.

Yellow polydymite is found as contorted and elongate veinlets and smears in talcose serpentinite in association with chalcopyrite, bornite, chalcosine and nickeliferous gel pyrite.

The nickeliferous mackinawite at Scotia is described as optically spectacular, and we believe them, as geologists are usually a staid bunch, not prone to such outbursts. It occurs as irregular intergrowths with pentlandite in the ore where it has undergone supergene alteration, and as elongate stringers and laminae in strongly deformed serpentinite layers within the ore and adjacent to it. It is pale blue-grey to dull golden-brown, with very strong bireflection and anistropism, with well defined colours.

Other Regions, Features and Areas containing this locality

References