EVOLUTION OF COMPOSITION OF TETRAHEDRITE AND ENARGITE SULFOSALTS IN THE MALETOYVAYAM EPITHERMAL Au-Ag DEPOSIT (<i>Kamchatka</i>)

Sulfosalts of the tetrahedrite and enargite groups from the Maletoyvayam epithermal Au-Ag deposit were studied using optical and scanning electron microscopy. We conclude that they were crystallized from acidic magmatic volcanogenic hydrothermal fluids under conditions of elevated oxygen level. Early sulfosalts of the pre-gold stage of the Maletoyvayam deposit, argentotetrahedrite-(Zn,Fe) and tetrahedrite-(Zn,Fe), associated with pyrite, arsenopyrite and galena, evolved with their enrichment in Te, Se and Cu. Increased activity of these elements caused by an increase in the oxidation potential of the environment led to the crystallization of subsequent stibiogoldfieldite, arsenogoldfieldite, and minerals of the enargite group, where the excess Cu content increased as the ore-forming system evolved. Au-bearing minerals are paragenetically associated with sulfosalts of the final stage of this evolution. The crystallization trend of sulfosalts (As→Sb→Te) at the Maletoyvayam deposit is also characteristic of other acid-sulfate type deposits, such as the Ozernovskoe and Prasolovskoe deposits, in contrast to the reverse trend (Te→Sb→As) typical for sulfosalts from adularia-sericite type epithermal Au-Ag deposits.