LATE STRUCTURAL CONTROL OF MESOTHERMAL VEIN-HOSTED GOLD DEPOSITS IN CENTRAL-VICTORIA, AUSTRALIA - MINERALIZATION MECHANISMS AND EXPLORATION POTENTIAL

Comparison of the structural relationships between five gold deposits in Ordovician rocks of the central Victorian slate belt reveals a similar history and structural control of gold mineralization. Large quartz veins, spatially associated with gold mineralization, such as the famous saddle reefs of Bendigo, formed during the second deformation, earlier than the gold mineralization itself. Where they were overprinted by the effects of the fourth deformation, they provided structural sites for gold deposition on their boundaries with country rock where brecciation, jostling and fracture were favoured. Access of fluids resulting from metamorphism and deformation to the brecciated, fractured and jostled blocks of country rock created conditions suitable for the precipitation of gold through a sequence of alteration, replacement and infill. The dominant structural relationships that resulted in the generation of these sites were (a), the high angle of the axial plane of the fourth deformation to earlier structures and (b), the presence, during mineralization of large, pre-existing quartz veins that acted as structural discontinuities on which brecciation could occur. These factors allow a predictive capacity for exploration in the region.