GOLD AND SILVER IN VOLCANOGENIC FLUIDS

Abstract

Gold and silver accompany the base-metal mineralization developed in the mantle magnesian basalts erupted during the great Tolbachik fissure eruptions of 1975-1976 and the arsenic-antimony-mercury minerals deposited in areas of hydrothermal discharge through deep crustal faults. The Au/Ag ratio is a possible index to pneumatogenic or hydrothermal mineral and ore deposition. Native gold associates with pneuomatogenic minerals, e.g. with quartz, at 500°C. In hydrothermal systems gold associates with quartz and calcite. In the favorable structural and morphological environment of the Tolbachik eruption, gold- and silver-bearing magmatic fluds enrich the ore and the altered rock simultaneously. Under hydrothermal conditions, gold and silver are redistributed between hydrothermal mineral deposits and hydrothermally altered rocks because of their different migration capacities, which is ascertained by the variations of the Au/Ag ratio. Generally, pneumatogenic mineral deposits and pneumatolytic rocks are promising for gold, as are hydrothermal deposits, whereas silver-bearing minerals are deposited in hydrothermally altered rocks.