REGIONAL FACTORS OF LARGE MASSIVE SULFIDE DEPOSIT FORMATION IN THE URALS

The article reviews the irregular pattern of the spatial and temporal distribution of the massive copper-zinc sulfide mineralization in the Urals, using a quantitative approach. The mineralization is mainly con centrated in Middle Devonian volcanics of the Magnitogorsk eugeosyncli nal megazone (more than 85% of the total reserves of copper and zinc i n the Urals), especially on its western flank, which contains all know n large deposits. The Tagil eugeosyncline, which is approximately the same size, hosts medium- and small-scale deposits, which hold less tha n 10% of the copper and zinc reserves in the Urals. In the Magnitogors k megazone, large massive sulfide accumulations were generated during the Hercynian eugeosynclinal cycle. This affected the southern, most t ectonically active segment of the Uralian polycyclic orogenic bell. Du ring the previous lower Proterozoic, Baikalian, and Caledonian cycles, similar associations of basaltic rocks, which host massive copper-zin c sulfide deposits, also accumulated in the belt. These cycles were re sponsible for a successive enrichment of the lithosphere with ore-form ing metals, and represented a long (1.2-1.3 Ga) preparatory stage for the final Eifelian-Givetian ore-forming stage. The predominant concent ration of ore deposits on the western flank of the Magnitogorsk megazo ne is related to the geodynamic evolution, in the context of plate-tec tonics theory, during all the cycles starting in the Riphean. Conjugat ion of ore-bearing volcanic belts with sublatitudinal faults was the c ause of the present irregularity in the distribution of the ore deposi ts, and the location of large deposits and ore districts within the be lts. The latitudinal faults reach deep-seated layers of the lithospher e in the Magnitogorsk megazone, and extend into the adjacent part of t he Eastern European Craton, where they form long-lived aulacogenes.