The actively mined Sunrise Dam orogenic gold deposit is located approximately 55 km south of Laverton, in the Laverton Terrane, along the Laverton Greenstone Belt. It is on the eastern margin of Lake Carey. This belt comprises voluminous mafic-ultramafic rocks and felsic to intermediate volcano-sedimentary sequences, including some banded iron formations.

The mine was previously owned by Placer Pacific Ltd and Delta Gold NL who called their eastern portion Sunrise, and Anglogold Australasia Ltd which called their western portion Cleo. They are now combined and named Sunrise Dam.

Sunrise was discovered in 1988 and mining operations commenced in May 1995. Cleo was discovered in 1991, and Accacia Resources commenced mining in February 1997. The ore is processed at the Granny Smith Mine facility.

Except for a small banded iron outcrop called Sunrise Hill, the relief is flat, composed of sand, gypsiferous dunes, salt pans and sheet wash deposits. The mine is contained within the regional and complex Laverton Domain, which hosts gold in metasedimentary rocks, which is not the case for most Yilgarn Craton gold mines.

The host rocks at Sunrise Dam are shallow dipping, interbedded Archaean metasedimentary, metavolcaniclastic and felsic to intermediate metavolcanic rocks. The metavolcaniclastic rocks are interbedded with banded iron formations, 2-10cm thick and grade into magnetite rich tuffs. Mafic intrusives, 20-40cm thick, postdates the metavolcaniclastic sequence on the western side of Cleo, intruded by quartz-feldspar porphyries at both Cleo and Sunrise.

The Sunrise Shear cuts through the deposit, dipping shallowly north north-west, 10 to 20 metres wide, and associated with a carbonate-sericite alteration halo 30 to 40 metres wide. Quartz veins are abundant throughout the deposit,5 to 20mm thick and up to 1 metre in length.

The Archaean rocks are weathered to 60 to 80 metres. There is a 27 metre overburden in the western part of the deposit. There is an additional 60 metres of sediment infilling a deep palaeochannel which trends south south-west through the deposit. This sediment is 20 to 60 metres of green-grey to white clay interbedded with pisolitic gravel lenses, saprolite debris and other material. The surface contains dune sand less than 3 metres thick.

The Sunrise Shear was the main conduit for the gold rich hydrothermal fluids. Primary mineralisation is pyrite replacing banded iron formations. Gold is also associated with quartz-ankerite-pyrite veins, and ankerite-silica-sericite-pyrite alteration of the intermediate volcaniclastic host rocks. Thin quartz-carbonate veins also host gold in the Sunrise part. Supergene mineralisation has developed in the weathered bedrock, and transported cover in the eastern part of the deposit. Gold is greatest in the lower saprolite of the regolith 65 metres below the surface.

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References