Australian Volcanic-Hosted Massive Sulfide Deposits: Features, Styles, and Genetic Models

The Cambro-Ordovician period has yielded the major development of volcanic-hosted massive sulphide (VHMS) deposits in Australia, resulting in about 12 million metric tons of contained metal (copper, lead, and zinc), concentrated in the Mount Read Volcanics (Tasmania) and the Mount Windsor Volcanics (Queensland). The Archaean and the Silurian constitute the next important episodes while the Devonian and Permian have produced isolated deposits. The deposits range from Cu type to Zn-Cu type to Zn-Pb-Cu type. The major VHMS-bearing districts are calc-alkaline in character. There is a wide range in variability of styles of Australian VHMS deposits including mounds, pipes, sheets, layered deposits, stacked deposits, stockwork and disseminated deposits, distal reworked deposits, and cyclic layered deposits. The mound deposits are considered to form from deposition of metal sulphides on the sea floor immediately around the hydrothermal vent. Sulphur isotope studies indicate that reduced seawater sulphate is a major source of sulphur in the deposit, whereas lead and strontium isotope results are compatible with the metals being derived by seawater convection and leaching from the volcanic pile and basement rocks. -from Author