Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
Petrology and gold content of adakitic granitoids of usthbelovskii complex in Makarevskii range of Gorny Altai
Abstract
The relevance of the discussed issue is caused by the need of researching petro-geochemistry and petrologic peculiarities of gabbrogranitoid massifs of Makarevskii range which are related spatially to gold occurrence. The main aim of the research is to study geological, petrological, geochemical features of all rock types of Ust-Belovskii complex in the range using canonic classification and experimental diagrams, which allow solving genetic problems. The methods used in the study. Rare and scattered elements were determined in rocks by inductively coupled plasma method on the mass spectrometry «ОРTIMA-4300», for Cu, Zn, Pb, Li - by the methods of ISP-AES, the rest elements, including REE, were determined by ISP-MS methods in the VSEGEI Laboratory (St-Petersburg). Absolute age of granitoids was defined by U-Pb method SHRIMP II by zircon in the VSEGEI Laboratory (St-Petersburg). Gold and bismuth were defined by the neutron-activation method in the Laboratory OI-GaG SO RAN (Novosibirsk). Results. The authors have corrected the absolute age of granitoids formation in Ust-Belovskii complexin Makarevskii range, it is 349?353+12,0 for Sosnovskii and Makarevskii massifs. The paper describes a direct zoning in intrusive massifs formation. 5 phases were detached in composition of intrusive: gabbro, diorites, tonalities, trondhjemites, leucogranites. More evolution phases of leucogranites are located in the center of massif but early gabbros are on the periphery. The authors estimated different petrochemical coefficients, indices, modules for the rocks of the complex used for decoding the genesis. Granitoids of range refer to high silica adakiticgranitoids. The ratios of strontium isotopes (87Sr/86 Sr for granodiorites of Makarevskii massif is 0,711(0,712) are identified by mantle nature of melts, formed with crust material contamination. Gabbro of early phase of Makarevskii range were probably generated by partial melting of slab, represented by fluid-metasomatized mantle peridotite. More late derivatesare indebted to mixing of basaltic and adakitic parent magmas. Generation of high silica adakites is related to direct melting of subducted oceanic crust, transformed at immersion into amphibolites and eclogites. Adakiticgranitoids of Makarevskii range were formed by partial melting (melting degrees is about 50 %) of 10 % garnet amphibolites. High fluid-saturation of melts resulted in transformation of ratios of many elements at occurrence of tetradic effect of M- and W-types REE fractionation. The paper indicates the space and paragenetic relation of different types of gold ore mineralization with granitoids of Makarevskii range.
