METATHOLEIITES AND INTERFLOW SEDIMENTS FROM THE CAMBRIAN HEATHCOTE GREENSTONE-BELT, AUSTRALIA - SOURCES FOR GOLD MINERALIZATION IN VICTORIA

Metatholeiites and interflow sediments of Cambrian age are exposed in the Lake Cooper quarry located in the northern segment of the Heathcot e greenstone belt, central Victoria, Australia. The exposed sequence i s 281 m thick and comprises nine massive to pillowed lava flows and se ven interflow sequences. The metabasalts from the Lake Cooper quarry h ave strong petrological and geochemical similarities to normal midocea n ridge basalts (N-MORB) and to metabasalts from greenstone suites els ewhere in Victoria, suggesting that they have not been exposed to exte nsive hydrothermal alteration. The interflow sediments in the quarry a re subdivided into units comprising finely bedded sulfides, layers of sulfidic carbonaceous argillites, chert, and sedimentary carbonate roc ks. Unusual mineral assemblages in these sediments, as well as their t race element concentrations and rare earth element signatures, suggest an exhalative volcanogenic origin. Whereas gold values in the tholeii tes from the Lake Cooper quarry generally remain below 2 to 5 ppb, gol d contents in the interflow sediments, which are also characterized by elevated As, Cu, and Zn values, range from <5 to 243 ppb and average 67 ppb. On the basis of sedimentological features and sulfide petrolog y, accumulation of the ore metals in these sediments is inferred to ha ve occurred during deposition of the exhalative precipitates, possibly as a result of extraction and transfer of ore metals from the thick b oninite sequence known to occur below the tholeiites in Victoria. Mass balance calculations show that remobilization of gold from the interf low sediments by metamorphic fluids and subsequent redeposition within dilatation zones and structural traps at higher crustal levels during the early to middle Paleozoic could account for a significant compone nt of the central Victorian gold province. Thus, these exhalative meta sediments might have played a vital role in accumulating, preconcentra ting, and providing the gold required to form the world-class turbidit e-hosted lode deposits in the Lachlan fold belt of Victoria.