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Cowarna opal mine, Cowarna Downs Station, Kalgoorlie-Boulder Shire, Western Australia, Australia

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Latitude & Longitude (WGS84): 31° 1' 12'' South , 122° 28' 22'' East
Latitude & Longitude (decimal): -31.02005,122.47295
GeoHash:G#: qdrpdbyp4
Locality type:Mine
Köppen climate type:BSh : Hot semi-arid (steppe) climate


Precious opal has only been found at two locations in Western Australia. This mine is 11 kilometres east south-east of the Cowarna homestead.

From 1972 to 1973, Russgar Minerals NL explored the site, resulting in three shafts being sunk. Although veinlets and pockets of precious and common opal was found, it was sub-economic to mine. During this period 15.6kg of precious opal was obtained from 500t of rock. The higher grade material displayed green, blue, yellow and blood-red colour flashes. Some of the material was cut and polished, rather than being retained as mineral specimens.

The opal deposit is hosted by a north trending zone of thinly bedded Archean graphitic quartz schist and tuff within an amphibolitic sequence. The mineralised strike length is 220m running north-south, but could possibly extend further in both directions. Sub-horizontal and vertical networks of silica veins occur in a 5 metre wide belt of thinly bedded graphitic quartz and tuff beds within amphibolites, intruded by quartz porphyry.

Veinlets and stringers of quartz, opaline silica, common and precious opal are found in quartz-kaolinite rocks, within shale, and an adjoining black glassy silicified unit. Precious opal is found in veinlets up to 1.2cm thick, and potch in veins up to 7.5cm thick. Some of the material shows a gradual change from quartz to common opal to precious opal within 2.5-5cm in the same vein. Specimens from the location are very rare.


Mineral List


3 valid minerals.

Rock Types Recorded

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Regional Geology

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

Neoarchean - Mesoarchean
2500 - 3200 Ma



ID: 3187518
Archean volcanic rocks

Age: Archean (2500 - 3200 Ma)

Comments: Yilgarn Craton

Lithology: Greenstone belt; mafic-ultramafic volcanic 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. [154]

Archean
2500 - 4000 Ma



ID: 725970
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). [5]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License



This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

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Fetherston, J.M., Stocklmayer, S., Stocklmayer, V.C.(2013): Gemstones of Western Australia- mineral resources bulletin 25, Geological Survey of Western Australia (2013): 113

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