Formation conditions of the Rudny Altai metallogenic province

Abstract

The results of previous geological, petrochemical, and metallogenic surveys conducted from the 1960s to the 1990s provide the geological and tectonic basis of this study. The unique mineral deposits of the Rudny Altai metallogenic province were formed in the Middle Paleozoic (S2–C1) at the junction between different structures of the Altai–Mongolian terrane: the Alei–Charysh–Tigirek rift (in the north) with the Korgon–Markakol’ island arc and Belaya Uba–Maimyr intra-arc trough (in the southwest). The Rudny Altai structural–formational zone that formed at the junction between these structures evolved as a magmatic arc and was characterized by the formation of granite–greenschist arches, volcanoplutonic magmatism and high heat and fluid flow (greenschist-facies metamorphism of Upper Silurian–Upper Devonian rocks and deposition of pyrite-bearing hydrothermal–sedimentary horizons, VMS and copper–VMS deposits and isolated base-metal ore bodies). The tectonomagmatic history of the Rudny Altai zone can be subdivided into several stages: Ludlow–Emsian, Late Emsian–Givetian, Frasnian–Early Famennian, Middle Famennian–Early Visean, and Late Visean–Serpukhovian. The island arc is represented by volcanic rocks of the andesite–dacite–rhyolite (early stage), basalt–rhyolite (Late Emsian–Eifelian), and basalt–andesite–rhyolite series (Late Visean). Volcanosedimentary strata (until the Givetian age) and turbidites up to 3–5 km thick were deposited in the interarc trough. Because of their metastable behavior, the volcanic rocks became actively involved in ion-exchange reactions with the formational waters, whereas the differences in hydraulic head between arches and troughs created favorable conditions for the transport of the metamorphic fluids, and the thermal gradient promoted thermodiffusion of divalent species of Mg, Pb, Zn, Cu, etc. toward the high-temperature zone and development of the high-Mg metamorphic–metasomatic alteration with a VMS–base-metal mineralization. As a result, ore deposits of different structural and genetic types were formed. Temperatures of ore formation (200–400°C) were controlled by thermal effect of pyrite dissolution and replacement reactions. The ore composition and regional metallogenic zoning were defined based on their position with respect to interarc and interarch troughs and the chemistry of the metal-extraction environment.