DISTRIBUTION OF GOLD IN THE OXIDATION ZONE OF THE URAL MASSIVE SULFIDE DEPOSITS - INFLUENCE OF THE PRIMARY ORE COMPOSITIONS AND CLIMATE

The influence of primary ore composition and climate on gold distribut ion in the oxidation zone of the Ural massive sulfide deposits is cons idered. As a result of a comparative analysis of data on 41 deposits o f the middle and southern Urals and the Mugodzhary region, three types of supergene distribution of gold are distinguished, and the type is determined mainly by the composition of primary sulfide ores: (1) chem ogenic type with an impoverished top and enriched bottom of the weathe ring profile characteristic for the iron and low-grade copper massive sulfide deposits; (2) residual type with Au concentration in the top o f the profile typical for the Cu-Zn-Pb-Ba massive sulfide deposits; an d (3) combined type characteristic for the copper, copper-zinc, and co pper-zinc-barite massive sulfide deposits. A more complicated composit ion of massive sulfide ores results in a reduced mobility of gold in t he weathering process, which is explained by the following reasons: (1 ) the concentration of sulfur oxyanions-the main gold complex agent-dr ops in the forming supergene solutions with a decrease in pyrite conte nt in primary ores, and (2) the reaction capability of gold in the wea thering environment is reduced with an increase in the amount of nativ e gold in massive sulfide ores and with an enlargement of its aggregat es sizes. The influence of the climate is determined predominantly for copper and copper-zinc deposits: an additional horizon of enrichment in the bottom of the subzone of the oxidized ores appears in semiarid and arid environments. Probable hypotheses as to the influence of clim ate on the supergene enrichment of gold are considered.