Tregurtha Mine, Broad Arrow, Broad Arrow Goldfield, Kalgoorlie-Boulder Shire, Western Australia, Australiai

Regional Level Types
Tregurtha Mine	Mine
Broad Arrow	- not defined -
Broad Arrow Goldfield	Ore Field
Kalgoorlie-Boulder Shire	Shire
Western Australia	State
Australia	Country

Tregurtha and Hughes are small mines adjacent to each other in the Mount Jewell area, north of Mulgarrie. They have a combined JORC Resource of 3.15 Mt at 1.32 g/t yielding 134 000 ounces of gold, and a combined JORC Reserve of 1.18 Mt at 1.40 g/t yielding 53 000 ounces. The deposits are granite hosted, and associated with sericite-silica-pyrite, and quartz-pyrite veining.

The area has been held by Kennecott Australasia Pty Ltd, CSR Minerals Pty Ltd, MPI Mines Pty Ltd, North Limited, Delta Gold, Pioneer Nickel Limited, Pioneer Resources Limited, Carrick Gold Limited, KalNorth Gold Mines Limited, and Norton Goldfields Limited. Pioneer, Carrick and Norton have been the most active exploring the deposit.

The prospects are located on the south-west corner of the Rainbow Dam Granodiorite, a 70 square kilometre north north-west orientated tear drop shaped pluton. It is bounded to the east by the Ringlock Dam Greenstone Belt, and west by the Scotia Greenstone Belt.

The prospects show weathering down to 70 metres, and a 30 metre depletion zone on top of the profile devoid of gold. Unaltered host rock is medium grained biotite granodiorite. High gold grades are found in the core of intensely altered biotite-sericite-pyrite, or sericite-silica-pyrite alteration in the shear zone. The zones grade out to sericite-chlorite alteration zones, then chlorite-epidote alteration. Gold is associated with quartz-pyrite veining.

There are three phases of alteration. Hematite alteration is characterised by deep red colouring of feldspar, and deep green chloritisation of amphibole, varying from a light dusting of hematite to total rock replacement. Potassic alteration is restricted to dusting on feldspar and biotite replacement of ferromagnesian minerals, associated with shearing. Lastly sericite-chlorite associated with gold showing the replacement of biotite with deep bottle green of granodiorite.

Gold is found in quartz pyrite veins, with pyrite less than 1% of the volume, often a trace, as fine, disseminated euhedra or films, associated with shearing. Quartz is clear to white, distinct from altered blue quartz in the granite. Gold is also found in biotite-silica, black, associated with strong shearing, and commonly associated with pyrite and quartz veining. Lastly gold is found with biotite-silica, associated with intense shearing, and post mineralisation thrusting.

The Tregurtha prospect shows as a series of anastomosing shears and mylonite zones, 15 to 30 metres thick, steeply dipping west, associated with chlorite-sericite alteration and periphery Foot Wall hematite alteration. It sits on the top of a rise covered by 2-5 metres laterised poorly cemented pisolithic gravel, calcrete, rock fragments and red soil.

The Hughes prospect sits on a splay structure, 30-45 metres thick, as a zone of intense biotite-chlorite alteration. It is located south-east from Tregurtha at the base of the slope, covered by a thin layer of soil over silcreted bedrock, outcropping locally as silcretised foliated granite porphyry.

Other Regions, Features and Areas containing this locality

References