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

Regional Level Types
Cowarna opal mine	Mine
Cowarna Downs Station	- not defined -
Kalgoorlie-Boulder Shire	Shire
Western Australia	State
Australia	Country

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.

Other Regions, Features and Areas containing this locality

References