Gold mineralization in shear zones within a turbidite terrane, examples from Central Victoria, S.E. Australia

Abstract

Central Victoria, in S.E. Australia, is regarded as the classical area for gold mineralization associated with saddle reefs, and with reverse faults, within a turbidite terrane. However, there is also an important contribution by steep, brittle shear zones to the mineralization and two such areas, Fosterville and Heathcote are the subject of this article. The shear zones hosting mineralization are sinistral transpressional structures that, while accommodating regional shortening, do it by both crustal thickening and lateral expulsion. The mineralization occurs at dilational jogs or bends within the zones. The shearing and mineralization postdate the main phase of folding and thrusting but predate widespread post-tectonic granitoid intrusion. It is postulated that the shears are a part of the initial phases of orogenic collapse which culminated in the emplacement of the granites, as well as sedimentation and acid to bimodal vulcanicity. Furthermore, it is argued that mineralization within the saddle reefs and reverse faults that characterize Central Victoria are also related to the initial phase of orogenic collapse. A final postulate is that orogenic collapse provides a common tectonic thread to some turbidite hosted, epithermal and Archean lode types of gold mineralization.