|Latitude & Longitude (WGS84):||31° 9' 54'' South , 121° 5' 6'' East|
|Latitude & Longitude (decimal):||-31.16527,121.08502|
|Köppen climate type:||BSk : Cold semi-arid (steppe) climate|
Located 60km SW of Kalgoorlie.
Located 26 kilometres south of Coolgardie.
This locality including the mineral species listed relates the the Nepean Nickel Mine. There was however a nearby locality called the Nepean Mine relating to gold which will be covered first. This was a historic gold mine operating only between 1897 to 1899, its short life a consequence of low gold grades.
The first mine manager was L.C. Wymond across 1897, but he died of pneumonia in April 1898 at only 34 years of age. Trial crushing from the new mine commenced in June 1898 with indifferent results. The mine was owned by Nepean (Western Australian) Gold Mines Limited who spent 12 000 pounds developing the mine, but by March 1899 it was reported the project had been abandoned by shareholders.
The Nepean nickel deposit was discovered from drilling by Metals Exploration in March 1968, and a mine started at the site in 1970, owned by Metals Exploration NL and Freeport of Australia as a joint venture. It was the second nickel mine in Australia after Windarra near Laverton in Western Australia. Till the mine closed in 1987, it produced 32 303 tonnes of nickel at an average grade of 2.99% Ni. The lease is now owned by Focus Minerals which holds most of the gold mines north of here to Coolgardie.
The ore bodies are two distinct but closely overlapping tabular ore zones dipping steeply at 80 degrees to the west, occupying contacts between serpentinite and metabasic rocks over a strike length of 670 metres and 340 metres. The mineralisation occurs to 476 metres deep and averages 1.5 metres thick.
The serpentinite units contacting the footwall ore bodies contain variable amphibolites of hornblende-plagioclase-cummingtonite-and quartz. The unit also contains metasedimentary rocks of biotite-plagioclase-quartz-garnet-staurolite-sillimanite, or cherty members of quartz-plagioclase-pyrrhotite-chlorite-cordierite-ankerite. Further, ultramafic rocks contain tremolite-chlorite-clinopyroxenes sometimes with olivine, or diopsidic clinopyroxenes, or sepentinities which are hypabasal, sill-like and periodolitic intrusives. The whole sequence is intruded by pegmatites and aplites being 80% albite and 20% quartz, with a slight deformation and
accessory molybdenite. Garnetiferous aplites are less common.
Some folding of the amphobolites and metasedimentary rocks has occurred. Two warping events have infuenced the ore bodies and the sulphides loads relocated into favourable structures. There is a north-east trending sub-vertical set of faults and fractures which parrallels the strike of the serpentinite, and post dates the pegmatites. The ore contact with the serpentinite is marked by shears which has influenced the shape of the ore body. Small areas on the ore footwall show diopside-calcite-clinozoisite-garnet and are related to nearly diopside veinlets, common in the amphibolite.
The primary mineralisation is 60% pentlandite, 20% pyrite, 18% pyrrhotite and the rest is chalcopyrite, cubanite, mackinawite and valerite. Cobalt and platinum is not significant. The ore zone is variable but a typical example would be at the base 0.75 metres of massive ore with 60% sulphides with serpentine or olivine matrix and accessory magnetite. Then a 0.45 metres zone of disseminated ore with 10-40% sulphides and abundant magnetite. Then a 0.3 metres zone of 5% disseminated sulphides in serpentinite with abundant magnetite.
The reaction zone between the orebodies and the metasedimentary rocks is up to 0.6 metres of chlorite, phlogopite and clinozoisite alteration of plagioclase sometimes proceeding to prehnite.
The supergene zone is 56-93 metres below the surface and is dominated by violarite in two different textures depending if it replaced pentlandite or pyrrhotite. Pyrite and marcasite are also produced in the supergene zone.
Commodity ListThis is a list of exploitable or exploited mineral commodities recorded at this locality.
42 valid minerals.
Rock Types Recorded
Select Rock List TypeAlphabetical List Tree Diagram
Entries shown in red are rocks recorded for this region.
- Igneous rock
- Normal crystalline igneous rock
- ⓘ Pegmatite
- Sedimentary rock and sediment
- Metamorphic rock
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
2500 - 4000 Ma
|mafic extrusive rocks 74248|
Age: Archean (2500 - 4000 Ma)
Description: Basalt, high-Mg basalt, minor mafic intrusive rocks; some andesite; agglomerate; mafic schist; amphibolite; dolerite; komatiitic basalt; carbonated basalt; basaltic andesite; mafic rock interleaved with minor granitic rock
Comments: igneous mafic volcanic; igneous mafic intrusive; synthesis of multiple published descriptions
Lithology: Igneous mafic volcanic; igneous mafic intrusive
Reference: Raymond, O.L., Liu, S., Gallagher, R., Zhang, W., Highet, L.M. Surface Geology of Australia 1:1 million scale dataset 2012 edition. Commonwealth of Australia (Geoscience Australia). 
|Neoarchean - Mesoarchean|
2500 - 3200 Ma
|Archean crystalline metamorphic rocks|
Age: Archean (2500 - 3200 Ma)
Comments: Yilgarn Craton
Lithology: Crystalline metamorphic rocks
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529.