Home – Home – Jornals – Russian Geology and Geophysics 2004 number 10

Volcanogenic hydrothermal and submarine hydrothermal-sedimentary pyrite-polymetallic deposits are known from the Asian part of Russia. They form in island-arc and rifting continental-margin structures and are related to basaltoid or differentiated basaltoid volcanism. The sulfide ores of the recognized groups of deposits are characterized by a sufficiently close composition but differ in contents of gold and silver.
The ores of volcanogenic deposits contain 1.0-1.5 ppm Au and 15-30 ppm Ag, with gold and silver distributed rather irregularly. The maximum contents of gold (up to 7-8 ppm) occur in high-temperature chalcopyrite-pyrite ores of the root zones and in higher-temperature barite-polymetallic ores of subsurface deposition. A correlation between gold and silver has been established.
The ores of large-scale volcanogenic hydrothermal-sedimentary deposits contain 0.09-0.16 ppm Au on average. The content of silver in them reaches 80 ppm, averaging 15-35 ppm. There is no principal difference in levels of gold accumulation in the ores from tuffaceous-terrigene-carbonate rocks and in the ores from pyrrhotite-bearing carbon-carbonate-silica schists.
Mineralization systems that form both hydrothermal and hydrothermal-sedimentary pyrite-polymetallic deposits of massive sulfide ores of close composition are genetically related to occurrences of submarine basaltoid volcanism of different geodynamic settings, and it is unlikely that initially they had radically different contents of gold and silver. Significant differences in sulfur isotopic composition of sulfides are established between volcanogenic hydrothermal and hydrothermal-sedimentary types of massive sulfide ores. Sulfur isotopic composition of volcanogenic hydrothermal deposits is close to the mantle values, whereas sulfur of volcanogenic hydrothermal-sedimentary deposits is of mixed mantle-crustal nature because the sulfates of sea water are involved into hydrothermal system. Low contents of gold in the ores of hydrothermal-sedimentary deposits can be explained either by its partial deposition in deep zones where hydrothermal solutions and sea waters mix or by the fact that, being dissolved in sea water, gold migrated to more distal facies of the basin of ore deposition. Contents of silver in ores of both groups of deposits are kept approximately at the same level, though in some hydrothermal-sedimentary deposits the ores are enriched in silver. The volcanogenic hydrothermal deposits show close patterns of distribution of gold and silver in ores of ancient and recent sulfide mineralization systems.