Syn-depositional fault controls on the Hellyer Volcanic-hosted massive sulphide deposit

Hellyer is a late-Middle Cambrian volcanic-hosted massive sulphide deposit, situated within the Mount Read Volcanics of western Tasmania. The effects of post-depositional folding and wrench faulting have been removed from the deposit to produce an interpreted Cambrian seafloor topographic contour map. This map reveals that the massive sulphide orebody formed within a north-south striking, fault controlled basin. Intersections of active, syn-depositional faults appear to have channelled hydrothermal fluids, and hence, controlled the location of massive sulphide formation. The most intense hydrothermal fluid flux was focussed on the intersection of three major structural elements:- i) north-south striking basin bounding faults, ii) a northeast striking fault, and iii) a northwest striking ridge. Metal-rich stringer veins within the footwall indicate that the orebody formed during the period of time when northeast striking faults were actively dilating due to northwest directed extension. During the waning stages of the hydrothermal system, basaltic magma rose up through a similar set of fissures and erupted onto the seafloor, burying and preserving the deposit.