Geology

The Bronzewing Gold Project is located within the Yandal greenstone belt which is approximately 250km long and 40km wide and trends north-northwest in the northern part and north-south in the southern part. The belt comprises a poorly exposed 2.7Ga greenstone terrain composed of metamorphosed volcanic, intrusive and sedimentary rocks. The province is characterised by Late Cretaceous to Cainozoic deep weathering and extensive alluvial and colluvial cover.

In the area of the Bronzewing mine, the greenstone succession is dominated by tholeiitic basalts and dolerite units with subordinate ultramafic, felsic and sedimentary sequences. The area to the south of the Bronzewing mine contains thick successions of dacite and rhyodacite volcaniclastic rocks with intercalated lenses of carbonaceous shale, less commonly chert, basalt and dolerites. The metamorphic grade is generally greenschist facies, but along the western and northern contacts with the granitoid bodies there are low to mid-amphibolite facies assemblages.

A recent structural analysis of the region proposed a four stage deformation history involving early thrusting followed by three further stages of deformation with gold mineralisation associated with the reactivation of pre-existing structures during the final deformation stage of regional east-west shortening.

All major gold deposits in the Yandal belt are hosted by iron rich units of greenschist metamorphosed tholeiitic basalt and dolerite that were trending at high angles to regional shortening during the mineralisation event. The iron-rich nature of the tholeiitic rocks is important because of the role of iron in wall rock sulphidation processes and the link between sulphidation and gold precipitation. Higher iron content generally favours the formation of iron sulphides by combination of iron from the wall rock with sulphur from the mineralising solution. The loss of sulphur from the solution destabilises the gold-sulphur complex and leads to gold precipitation. An independent but equally important factor making the tholeiites important as gold host rocks is their tendency to fracture under elevated fluid pressure, leading to extensive fluid ingress. These two factors make tholeiitic rocks important gold targets and the iron-rich nature almost certainly contributes to the generally higher gold grades at these deposits.

Mafic rocks of tholeiitic composition are dominant at various gold deposits including the Discovery, Central and western zones at the Bronzewing mine itself, Cockburn and Lotus at Mt McClure, Sundowner (northeast of Bronzewing) and Mount Joel (also northeast of Bronzewing).

Various gold deposits at Dragon-Venus, Challenger, Parmelia and Success, along the Southwest Mt McClure Trend, are more tightly controlled, in a structural sense, than the larger deposits. Their smaller size is probably due to the less continuous nature of the hosting thrust faults and their mainly non-mafic host rocks.