Abstract:
Alpine-type dunite-harzburgite-lherzolite massifs have long attracted much attention of geologists as reference objects for geological and petrological models and as massifs hosting economic deposits of Cr, Ni, and asbestos. Russia''s largest deposits of Cr ores, Ni ores in weathering crusts, as well as deposits PGE, asbestos, and some other minerals are hosted by Alpine-type ultrabasic massifs of the Urals. The results of our long-term fieldwork and of the experimental and theoretical research of the mineralogy, petrography, and metallogeny of Uralian Alpine-type ultrabasites and the analysis of literature data on analogous rocks elsewhere led us to the following conclusions. The evolution of the mineral assemblages of the Alpine-type ultrabasites occurred in six major stages: mantle, regional metasomatic, pegmatitic, retrograde and prograde metamorphic, and hypergenesis. The Alpine-type ultrabasites evolved during the metamorphic stage in a closed system and could exchange only energy with the environment. The driving forces of the evolution of the mineral assemblages were variations in the intensive parameters of the mineral-forming medium, namely, a temperature and pressure decrease, variations in the fluid regime and in the pH and Eh. Certain ranges of thermodynamic parameters, and thus, certain types of mineral assemblages, corresponded to the typomorphic rocks of each stage.
