|Latitude & Longitude (WGS84):||30° 43' 50'' South , 121° 28' 52'' East|
|Latitude & Longitude (decimal):||-30.73069,121.48098|
|Köppen climate type:||BSh : Hot semi-arid (steppe) climate|
The Mount Percy Gold Mine is 2 kilometres north-east of the Kalgoorlie city centre. It is part of four shallow pits named, Mount Percy, Sir John, Union Club, and Mystery, accessing regolith gold. The pits are virtually co-joined. While by no means the most interesting geological deposits in Western Australia, they have been much studied, due to their proximity to Kalgoorlie and the Golden Mile.
Ore body geology is included under the Mystery Gold Mine Mindat locality, as it is virtually the same as Mount Percy. This section will focus on the host rocks.
The mines occupy a hinge zone and steep east dipping limb of the Kalgoorlie Anticline. This consists of the Hannans Lake Serpentine, Devon Consols Basalt, Kapai Slate and Williamstown Dolerite. It is cross-cut by a series of north trending, west dipping dextral faults named Maritana, Reward, Charlotte and Mystery Faults. The Golden Mile Dolerite is found to the east, and Black Flag Beds to the west. Gold is found at Mount Percy in quartz veins and felsic porphyry intruding the Devon Consols Basalt.
Open pit mining was conducted from 1985 to 1995. The mineralised zone is 30 metres wide by 1800 metres long, separated from the Mystery Zone gold deposit by 300 metres of intermittently mineralised rock. The pit was partially backfilled in 1998. The Mount Percy processing plant was decommissioned in 1997, and the 7 ha site rehabilitated in 2001.
Historically, mining activity before this was only found in the late 1890's, although prospector activity may have occurred after. From 1896 to 1898, the African Gold Recovery Company developed the mine. This company had been an early entry on the South African Goldfields, and had patented the cyanide gold extraction process. They owned a number of gold mines in Australia at the time. Telluride was discovered in 1897, in areas of rich gold, being the first discovery in the Kalgoorlie area outside the Golden Mile. GML 4468E.
The regolith consists of 1 metre thick calcareous soil, 1-5 metres of lateritic residuum, 10-15 metres of mottled and plasmic clays, 40-50 metres of saprolite, and basal saprock. A shallow palaeochannel, 5-7 metres deep can be seen in the northern wall of the pit.
The Hannans Lake Serpentine consists of biotite-talc rocks; talc-chlorite rocks; and fuchsite ultramafic rocks. The biotite-talc rocks are fine felted aggregates of talc and Biotite, the latter intergrown with chlorite. There are also porphyroblasts of magnesite and dolomite to 1 mm, and albite 0.2 mms. Throughout the mass is carbonates coalescing into veinlets.
The talc-chlorite rock is cross cut by networks of carbonate-quartz veins and carbonate-albite.
The fuchsite ultramafic rocks show dolomite, magnesite, quartz, fuchsite, some chlorite, accessory rutile, and pyrite (with gold), the mass green, especially at porphyry contacts. Some areas also include albite alteration, cross cut by numerous carbonate-quartz-albite veins. Some of the veins contain fuchsite, and a few dark green vanadiferous muscovite roscoelite.
Meanwhile there are three types of porphyries which intrude the host rocks. The first is pale grey to white with green fuchsitic xenoliths, some carbonate, chlorite and fuchsite, in a groundmass of albite, in part replaced by K Feldspar, with accessory rutile, pyrite and other sulphides.
The second is pale buff to grey, with carbonate phenocrysts surrounded by rutile and sphene. The groundmass is carbonate, white mica, albite, and quartz, but no feldspar.
The third is pale grey, bleached when next to narrow cracks, with scattered twinned albite phenocrysts, and carbonate, chlorite, and mica, in a groundmass of albite, carbonate and quartz. Pyrites and other sulphides are locally abundant.
Gold is found associated with fine grained dissemination and veinlets of pyrite, and narrow quartz and quartz-tourmaline veining within porphyry, and the adjacent fuchsite-carbonate rock. Some veins have sulphide alteration haloes.
For a photograph see the Mystery Gold Mine Mindat locality. The Mount Percy mine is the pit to the left in this photograph.
Commodity ListThis is a list of exploitable or exploited mineral commodities recorded at this locality.
23 valid minerals.
Rock Types Recorded
Select Rock List TypeAlphabetical List Tree Diagram
Entries shown in red are rocks recorded for this region.
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 intrusive rocks 74263|
Age: Archean (2500 - 4000 Ma)
Description: Mafic intrusive rocks, medium to coarse-grained; layered mafic to ultramafic intrusions - dolerite, gabbro, olivine gabbro, peridotite, pyroxenite, leucogabbro, quartz dolerite, quartz gabbro, gabbronorite
Comments: igneous mafic intrusive; synthesis of multiple published descriptions
Lithology: 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 volcanic rocks|
Age: Archean (2500 - 3200 Ma)
Comments: Yilgarn Craton
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.