GEOLOGICAL CONDITIONS OF THE LOCALIZATION OF LARGE BASE-METAL DEPOSITS IN THE RUDNYI-ALTAI

In the Rudnoaltaisk Base Metal Belt, occupying an area of about 40 000 km(2) in Kazakhstan and Russia, there are more than 1000 mineral occu rrences and massive sulfide base metal deposits, including more than 7 0 commercial ones. About 70% of their total initial reserves of Pb, Zn , and Cu are concentrated in the six largest deposits (Ridder-Sokol, T ishin, Zyryanov, Maleev, Belousov, and Orlov). Based on the generaliza tion and analysis of numerous published and unpublished data of Altai geologists and geological institutions, as well as personal investigat ions, this paper presents geological characteristics of the aforementi oned large deposits and discusses the conditions of their localization . The conclusion about their genetic relationship with the basalt-rhyo lite calcareous-siliceous-terrigenous association (BRTA), which is a c omponent of the volcano-plutonic belt. The belt is formed in the south western active margin of the Caledonian Altai-Sayan continental megabl ock situated over the Zavaritsky-Benioff Zone. The ore-bearing basalt- rhyolite terrigene association was formed under the conditions of cont inental crust extension, uplift the mantle and basalt layer, and activ ization of the interaction between the mantle and crust. Systems of no rthwestern and sublateral deep faults, particularly their conjugations , predetermined the development of volcanic centers, volcano-tectonic structures, and the ore group localization. The stratified localizatio n of deposits in the basalt-rhyolite terrigene association is stipulat ed by multistage volcanism. The main ore deposition occurred during th e waning of volcanic activity and the sedimentary lithofacies depositi on; this is indicated by the localization of ores mainly at the upper horizons of volcanogenic-sedimentary complexes. Large deposits are cha racterized by the following major features of geological constraints r elative to medium and small deposits. Large deposits are located in tw o, older, most productive Emsian and Emsian-Eifelian volcanogenic-sedi mentary complexes. They are notable due to a closer spatial associatio n with anticlinorium structures and conjugations of major sublateral a nd northwestern deep faults. These conjugations were the main centers of deep magmatic activity during the syn- and postvolcanic periods; th is is reflected by the presence of large intrusive massifs (end produc ts of the evolution of magmatic centers) under large ore fields and de posits. The main ore lodes of large deposits are situated in thick (se veral dozen and hundred meters) sedimentary deposits, indicating the d uration of facial conditions that were favorable for the hydrothermal- sedimentary accumulation of ores and their subsequent conservation. La rge deposits are characterized by an integrated combination of the abo ve-mentioned geological factors and localization constraints.