Edna May Gold Mine, Westonia, Westonia Shire, Western Australia, Australiai

Regional Level Types
Edna May Gold Mine	Mine
Westonia	- not defined -
Westonia Shire	Shire
Western Australia	State
Australia	Country

Open cut gold mine, currently operated by Evolution Mining. The Edna May mine is located near the northern end of the Westonia Greenstone Belt in Western Australia's Archaean Yilgarn Craton. The Westonia Greenstone Belt comprises a series of outliers of predominantly amphibolite-grade metamorphic rocks extending approximately 100km WNW from near Edwards Find, south of Southern Cross. The remainder of the terrane comprises granitic rocks and their metamorphosed equivalents.

The Edna May gold mineralisation is hosted within three en echelon tonalitic gneiss intrusions, namely Edna May, Greenfinch and Golden Point. The deposits are bound to the north and south by an ultramafic ampbibolite.

Current resource at Edna May is 48Mt at 1.0 g/t Au. Current annual production is 70-80koz Au.

A Western Australian Museum field trip to the mine took place in October 2009, during which full access was granted to collect from historical mine dumps and stockpiles. Two days of collecting yielded very little specimen material. None of the interesting secondary lead minerals reported by Simpson (1948) e.g. crocoite and tungsten-bearing wulfenite, were found. Such minerals in the oxide zone of orogenic gold deposits are often associated with high grade secondary gold mineralisation, and hence were usually earmarked for processing.

The deposit is found in a small greenstone roof pendant in granite. The sequence shows metamorphosed interbedded mafic schist, amphibolite schist, coarse grained amphibolite, hornblende-biotite schist, gneisses and some ultramafic rocks. The greenstone is sheared and highly contorted, dipping 50 degrees north-east. The greenstone is intruded by pegmatite and hornblende dykes.

The host to the mineralisation is an elongate north-west trending lens of biotite-hornblende gneiss, 420 metres long by 140 metres wide, as an enclave in mafic rocks.

The mineralisation is within thick folded quartz pegmatite reefs in fissures. The quartz is milky white and translucent. The source states rows of fluid inclusions have been found in the quartz. The gold is disseminated in the quartz, some feldspar and wolfram mineralisation, rather than in sulphides, although paradoxically gold grades are directly related to sulphide abundance. Gibb-Maitland states there was considerable masses of scheelite and wolframite, several inches in diameter in coarsely crystallised pegmatite veins, below the 550 foot level.

There are four parallel reefs called Edna May, South, Middle, and Consolidated. The reefs fold into an anticline, pitching 50 degrees north-west, and intersects at the surface as a boomerang shaped outcrop (now likely gone through mining). The reefs are broken into vertical offset sections by low angle faults, cut by granite dykes, and mafic dykes.

Geochronology

Mineralization age: Neoarchean : 2744 Ma to 2726 Ma

Important note: This table is based only on rock and mineral ages recorded on mindat.org for this locality and is not necessarily a complete representation of the geochronology, but does give an indication of possible mineralization events relevant to this locality. As more age information is added this table may expand in the future. A break in the table simply indicates a lack of data entered here, not necessarily a break in the geologic sequence. Grey background entries are from different, related, localities.

Geologic Time				Rocks, Minerals and Events
Precambrian
	Archean
		Neoarchean		ⓘ Molybdenite (youngest age) 2726 Ma ⓘ Molybdenite (oldest age) 2744 Ma

Other Regions, Features and Areas containing this locality

References