ORE GENESIS OF THE OLIMPIADA GOLD DEPOSIT (RUSSIA, YENISEI RIDGE)

The Olimpiada gold-sulfide deposit in the Yenisei Ridge, as per the results of additional exploration of the recent years, has confirmed its uniqueness in terms of reserves (1560 t) and ore extent in the depth (1500 m). Meanwhile, no indicators of thinning out and change in mineralization parameters have been noted. Oxidized ores mined out to date were developed in the upper part of the deposit. About 200 t of metal have been mined from them. The deposit is confined to the silicate and carbonate band of the Lower Riphean Kordinskaya suite clastic stratum. Granitoids separated from the deposit at 1.5 km and above surround the deposit. Introduction of intrusions in the Tatar-Ishimbinskaya tectonic zone assisted in the formation of compensation synformal depressions (Innokentyevskaya and Chirimbinskaya synclines) in the contact zones of intrusions united by the antiformal rock unit (Medvezhinskaya anticline). These connected W-shaped structural elements represent the structure of the ore field. Subhorizontal shifts in the area shaped the magmatogene structure into tectonic syncline and anticline folds. The ore bodies are concentrated in fold curves and rock bends at limbs. The northeastern curve of the Medvezhinskaya anticline has the highest ore content. There, the deposits of the northern and southeastern limbs of the Medvezhinskaya antiform are connected and represent a single ore body sloping to the southeast. No indicators of thinning out at the depth have been revealed. The micaceous-quartz-carbonate matrix of the sulfide-disseminated ores has been boudinaged, milonite-altered and folded into minor folds up to plication. The main ore forming elements, including Au, Ag, Fe and Sb, form dissemination of native minerals, sulfides, sulfosalts and tellurides. In terms of the mineralogical and geochemical composition the ores are divided into gold-arsenic and goldarsenic-antimony ores separated spatially. The gold-arsenic-antimony ores with the geochemical mercury and tellurium impurity are confined to the northeastern deposit of the ore body. Metamorphism in the tectonic-metamorphic zone of the deposit occurred at the temperature of 400-420 degrees C and the pressure of 3-4 kbar in chlorite and biotite zones, and in the garnet and margarite zone - at 580-605 degrees C and the pressure of 7.2-7.5 kbar. Metasomatosis of silicate and carbonate rocks with skarnoid formation (Act+CZo+Gar+Sph) occurred at 320-480 degrees C and the pressure of 1.3-1.5 kbar, and of acidic metasomatites (silicified and sericitized rocks) at T = 290-380 degrees C and P = 1.0-3.0 kbar. The polystage hydrothermal quartz-gold-sulfide process of aggregate formation occurred in the interval of 460-110 degrees C. The age of the main stages of ore formation is within 817-660 Ma. The industrial ores of gold-arsenic composition have the age of 758-803 Ma, and the gold-arsenic-antimony ores are 660-795 Ma old. The isotope and geochemical studies testify to the participation of the crust and mantle substance in the deposit formation. Aquatic-chloride-carbon dioxide solutions saturated with hydrocarbons participated in the ore substance transportation.