TASMANIA- AN ISLAND OF POlENfIAL Stratigraphic-facies associations and their relationship to mineraUsation

The highJy mineralised Cambrian Mount Read Volcanicsform an arcuate belt along the western margin of the Precambrian Tyennan region. Volcanic-Iwsted massive sulphide (VHMS) deposits at Hellyer, Que River, Rosebery, Hercules, and Mt Lyell occur in a sequence of deformed, regionally metamorplwsed (lower gl'eenschist facies), and hydrothermally-altered volcanic rocks. The Mount Read Volcanics can be broadly subdivided into a lava-rich eastern and central belt with the Eastern quartz-phyric sequence interfingering with thefeldspar-PhYric Central Volcanic Complex. They both interfinger with the western volcano-sedimentary successions (Yolande River succession, Dundas Group and the Mount Charter Group). The youngest part of this volcanism is time equivalent to a belt-wide periodofandesitic-basaltic volcanism and VHMS deposit formation (Hellyer, Que River and some at Mt Lyell). A period of extension and rifting occurred at this time, with a tlwleiitic dyke swarm concentrated along the Henry Fault and tlwleiitic pillow basalts in the Henry Fault wedge. Recent volcanological studies have suggested that thefinal phase of volcanism which produced the widespread mass-flow deposits of the Tyndall Group and Southwell Subgroup resulted in an extensive basal marker sequence. If the widespread extent of this marker sequence is confirmed then the previous position of the Rosebery-Hercules mineralisation, as early during the Central Volcanic Complex formation, will result in a re-interpretation which places tlwse VHMS deposits at time-equivalent or slightly younger than the Que-Hellyer mineralisation