T39 Advances in the Understanding of Tectonic Settings and Structural Control of Ore Deposits

Sunday, 16 October 2005
1:30 PM - 5:30 PM

TERRANE- TO CAMP-SCALE SIGNATURES OF GOLD MINERALIZING SYSTEMS OF THE YILGARN CRATON, WESTERN AUSTRALIA

Paper number: T39-1
Program: Technical Sessions
Time: 1:30 PM – 1:45 PM

Authors

Abstract

Poorly exposed Neoarchean granite-greenstone terranes of the eastern Yilgarn Craton include some of the world's most highly-mineralized belts hosting many world-class gold deposits (Robert et al., 2005). Signatures of the mass and energy flux responsible for these gold mineralizing systems are visible at a range of scales using geological and geophysical data sets. At terrane-scale, highly-mineralized belts are confined to older crustal domains containing thin (<7 km) greenstone sequences with abundant komatiites. Under the greenstones, felsic upper crust is dominated by undulating sets of strong seismic reflections interpreted as low-angle shear zones altered by fluids during orogenesis and mineralization. Seismic data show mid- to deep crustal structures and mid-crustal thrust duplexes that are consistent with lithospheric-scale orogeny involving west-directed (trans)compression. Terrane-bounding fault systems (Ida, Ockerburry, Hootanui) are generally poorly mineralized.

At belt-scale, syntectonic sedimentary basins unconformably overlie folded greenstones as an integral component of the orogen. The youngest felsic-intermediate magmatism sourced from subduction-modified mantle is localized close to linked belt-scale structures. Late extension is temporally associated with emplacement of abundant potassic granites. Reflective fault systems seen on seismic profiles appear linked and provide connecting pathways for hydrothermal fluids to move to depositional sites. At camp-scale, domal or anticlinorial structures (which are breached by later faults) are spatially associated with the region's larger gold deposits (Kalgoorlie, Kanowna Belle, St Ives, Wallaby) and provide favorable focusing for fluids (Henson et al., 2004). Deposits are hosted in structures subsidiary to these belt-scale faults and show evidence of multiple ore-related fluids (St Ives: Walshe et al., 2003). Integration of these signatures across scales permits a better understanding of the Yilgarn's gold endowment and provides constraints for effective exploration targeting.