Abstract:
The great bulk of massive sulfide deposits in the Urals are related to Paleozoic basalt-rhyolite and basalt-andesite-dacite-rhyolite volcanic rock associations of ensimatic island arcs. According to Ivanov and Loginov [1], Prokin [2], and other researchers, their geological section consists of the following units (from bottom to top): (1) basic volcanics, (2) ore-bearing sequence of acid volcanics (thickness 300-700 m, maximum 1.5 km), and (3) volcanosedimentary and sedimentary rocks. The massive sulfide deposits are hosted in the acid volcanics that fill paleodepressions situated between extrusive domes or on their slopes [3,4]. However, not every paleodepression is ore-bearing. Identification of ore-bearing and barren paleovolcanic depressions is an essential issue in forecasting massive sulfide ore mineralization. Elucidation of this issue is important for understanding processes of ore genesis. Recent studies have shown that processes not only in the mantle and crust but also in the exogeneous environment (formation of volcanic rocks from mantle-crustal melts and specific features of volcanic edifices) control the ore formation. Together with juvenile sources of ore-forming materials, meteoric water participates in the formation of massive sulfide ores, and a considerable amount of ore material is leached from host rocks [5-8]. Therefore, the volcanic paleodepressions should be regarded as both ore-bearing and ore-forming systems.