THERMOBAROGEOCHEMISTRY OF ORE FORMATION PROCESSES IN MOLYBDENUM-TUNGSTEN DEPOSITS OF THE GREISEN GROUP IN CENTRAL KAZAKHSTAN

Abstract

Molybdenum-tungsten mineralization of the greisen group in Central Kazakhstan was formed during orogenesis and stages of tectono-magmatic activation. The Dzhungar-Balkhash geosyncline region occupies a special geological and metallogenic place in the Central Kazakhstan ore province. Here, during the Late Hercynian orogenesis, acidic intrusions were formed, with which all molybdenum and tungsten deposits are spatially, structurally, and in terms of time of formation connected. 18 ore regions have been identified, more than half of which are located in the Uspenska zone of crush and are associated with greisens of various facies. There are two morphotypes of deposits – endomorphic veined and supraintrusive stockworks. Greisens were formed in the frontal zone of the autometasomatites column with the participation of high-temperature, essentially gaseous acid solutions, which, with a decrease in temperature (>470–300 °C), underwent compaction and condensed in the form of post-magmatic distillates at a depth of 5–4 to 2.5–1.5 km. The distillates were enriched in halides, CO2, H2O, and other volatile compounds. The separation of melts-fluids from magma chambers and their evolution occurred either under the condition of retrograde boiling of magma, or as a result of the gradual separation of melts-solutions ‒ with the formation of melts-solutions with CO2 and a residual melt-solution with high-density halogen ore-forming fluids. Separation from the magma-ore generating chamber occurred in different ways. During the development of contractional fracturing in supraintrusive host rocks, an arch effect was formed and a noticeable decrease in pressure occurred, which contributed to the «suction» of fluid from the magma-ore-generating source with subsequent extraction of rare metals. Molybdenum-tungsten deposits in the region have been formed under pneumatolitic-hydrothermal conditions during five stages of mineralization from solutions of high salt concentration (>65‒27 wt. % NaCl) and high pressure and its significant fluctuations (from 165 to 25 MPa).