Nevoria Gold Mine, Marvel Loch, Yilgarn Shire, Western Australia, Australiai

Regional Level Types
Nevoria Gold Mine	Mine
Marvel Loch	Loch
Yilgarn Shire	Shire
Western Australia	State
Australia	Country

A gold mine started 1984.
Skarn deposit in a banded iron formation.

Nevoria is a reduced skarn assemblage containing major amounts of ferrous iron in garnet and pyroxene formed from Fe-rich rocks at great depth (10 to 15 kilometres) in regional metamorphic terranes. Skarns are interesting and Nevoria has possibly the most complex geology of any gold mine in Western Australia. Nevoria is 10 kilometres south-east of Marvel Loch. No specimens have been seen from the mine which is a shame.

Early historic information is difficult as it was described as an area containing many leases and workings of individual prospectors. The name 'Nevoria' in this sense first appears in 1917, although mining is noted in the general area from 1905. Leases were consolidated in 1933 by the Nevoria Gold Mine Company, which was initially a British concern but was later taken over by South Africans. What followed was decades of procrastination, as the company sought funds to develop the mine. Drilling and minor building construction began in 1947, and dragged on till 1952 when the company went into liquidation. In 1956 the lease was purchased by Western Mining Corporation under its subsidiary Great Western Consolidated, who operated many gold mines in the region in the 1950s and 1960s. They opened a mine here till 1966. The mine was operated by the Sons of Gwalia Limited in the 1980s. Later St Barbara Limited mined here at what it called the Norton Pit till at least 2008, but presently (2013), it only operates at the Marvel Loch mine.

Most skarns are associated with shallow Phanerozoic plutons intruding unmetamorphosed sedimentary rocks. However, Nevoria is a mesothermal gold lode deposit with skarn alteration in a regional metamorphic terrane. The reference states little is known about the development of these skarns, but appear to be hybrid between a regional metamorphic environment and the more typical Phanerozoic plutonism. They include very Fe-rich rocks, and reduced assemblages of garnet and pyroxene, but also have Au-As-Bi-Te mineralisation of younger gold skarn deposits.

The mine occurs in the Southern Cross Greenstone Belt of greenschist to amphibolite, underlain by the Ghooli Dome, a composite grandiorite-granite batholith. Under the Nevoria open pit, this also contains massive pegmatites, and post mineral pegmatite dykes cut orebodies also in higher levels in the mine. The orebodies are contained in three steeply dipping horizons of grunerite-quartz in iron formations, interbedded with fine-grained ultramafic to mafic amphibolites. The iron formation hosted skarn contains 6.7 g/t Au, 2-3 g/t Ag and less than 0.1 wt base metals. Au is also present in the iron formation itself and ultramafic/mafic rocks, but at sub-economic grades in the latter. Au distribution is variable with high grades in skarns near contacts with metamorphic rocks.

The skarn orebodies at Nevoria occurs as stratabound replacements of grunerite-quartz iron formations adjacent to flattly dipping quartz veins. Major prograde minerals are hedenbergite, locally intergrown with minor calcite and rarely scheelite, medium grained ferro-actinolite and ferro-hornblende. Parrallel to the iron formation mesobands and at the margins of cross-cutting quartz veins is almandine with ferro-hornblende, biotite, ilmenite and tourmaline. Veins of garnet-pyroxene-actinolite-hornblende occur in tholeiitic and komatiitic amphibolites but not in the iron formation. Retrograde alteration minerals include Fe rich chlorite, muscovite and stilpnomelane. Gangue minerals are intergrown with disseminated to massive pyrrhotite, and minor chalcopyrite, loellingite, arsenopyrite, pyrite and scheelite. Gold occurs in native form either enclosed by pyrrhotite, or in skarn silicates like hedenbergite, actinolite, almandine and quartz; often associated with tsumoite, Bi-Te sulphides and maldonite alloy, locally exsolved to native bismuth and native gold.

The skarn is also found in the ultramafic/mafic amphibolites with zoned garnet-pyroxene replacement veins with irregular boundaries. The veins consist of a core of grossular garnet, and outer margin of diopside, or dark orange-red grossular-almandine garnet, with an outer rim of the very uncommon vanadium rich goldmanite garnet. Goldmanite is also found rarely as isolated crystals enclosed in clinozoisite. Minor plagioclase, microcline and scheelite is intergrown with the garnet and pyroxene. These zones are comprised of numerous alterating bands of reduced diopside-hornblende, almandine-hornblende and almandine-cummingtonite-plagioclase skarn. Retrograde minerals in the veins include clinozoisite-calcite-quartz assemblage, filling cracks in the grossular garnet, and aggregates of muscovite and prehnite are found replacing feldspar. Pyrite and chalcopyite is rarely found disseminated through the assemblages.

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References