Controls on gold and silver grades in volcanogenic sulphide deposits (84/P210) AMIRA Progress Report, November 1986

INTRODUCTION Restatement of Aims: To investigate the geological and geochemical controls on the distribution of precious metals within volcanic-hosted massive sulphide deposits, with the objective of developing exploration models useful for the discovery of further precious metal-rich deposits. Background: Due to the high concentration of gold and silver in the Western Tasmanian volcanogenic deposits, the project has initially concentrated on the documentation and study of gold-silver accumulation along the Mt. Read Volcanic Arc. A four-pronged approach has been adopted on the Tasmnanian deposits: 1) Detailed studies of precious metal geology and geochemistry at Rosebery and Que River, the two richest deposits. 2) Geology and geochemistry of a barren sulphide system, Lake Selina, to evaluate why some volcanic hydrothermal systems are devoid of precious and base metals. 3) A study of gold mineralisation along the Henty Fault Zone, a major structure which dislocates the Mt. Read Volcanic Arc and has been the focus of hydrothermal activity. 4) Research into the chemistry of the Mt. Read Volcanics to determine whether there is a relationship between gold mineralisation and volcanic rock chemistry (either primary or alteration chemistry). To complement the Tasmanian studies, three Western Australian Archean volcanogenic deposits (Gossan Hill, Scuddles, and Teutonic Bore), and a Queensland deposit (Balcooma) have been included in the project for comparative purposes. This Report: This second major report marks 15 months of research since commencement of the project in August 1985. The first report (April 1986) dealt mainly with research on: - geology, structure, and metal distribution of the PQ lens and P-north lens at Que River. - a chemical data base for the Mt. Read Volcanics. This report covers further research developments on the Tasmanian deposits plus a comprehensive section on the Archean massive sulphides. Progress this year has been excellent and I would like to give special thanks to all the AMIRA team members at the University of Tasmania for their dedication, support, and fine standard of research. Ross Large Project Leade