Itakin gold deposit: isotopic composition: probable sources of ore matter (Eastern Transbaikalia)

It has been established that the Itakinskoye gold deposit is similar to many Mesozoic gold deposits of Eastern Transbaikalia according to the conditions of formation, mineral and geochemical features. The study of the elemental composition of rocks and ores of the deposit was carried out in the analytical laboratories of the Geological Institute of the SB RAS (Ulan-Ude) and in the Center for Collective Use of Multi-Element and Isotope Studies of the SB RAS (Novosibirsk). The content of elements in rocks and ores was determined by the X-ray fluorescence method on the ARL Perform'X 4 spectrometer. The concentrations of rare earth elements were measured by the ICP-AES method. The determination of the oxygen isotopic composition was carried out using the MIR 10-30 installation of a laser heating system with a CO₂ laser with a power of 100 watts and a wavelength of 10.6 microns in the infrared region, in the presence of the BrF5 reagent. The isotopic composition of sulfur in sulfides was analyzed in the center for collective use of the Siberian Branch of the Russian Academy of Sciences on a Finnigan MAT Delta gas mass spectrometer in the double-inlet mode. The values of 8³⁴S (Q) are given relative to the CDT standard. There are three ore sections at the deposit - Gavrilovsky, Antimyanaya Gorka and Maleevsky. Three main paragenetic ore associations are noted at the deposit: quartz-arsenopyrite (productive), quartz-polymetallic (productive) and quartzantimonite. A distinctive feature of the Itakinsky deposit is the wide development of quartz-antimonite mineralization. It is determined that the calculated isotopic composition of oxygen in the fluid in equilibrium with quartz of the productive stage (260-205 °C) varies from 2.69 to 10.26 %o. Most of the values fall within the range of + 5.5 % - +9.5 %o, corresponding to the fluid of magmatic nature. The magmatic source of mineralization is also confirmed by the isotopic composition of sulfur sulfides. Thus, for the fluid that deposited pyrite at 300 °C, the values of 8³⁴S_H2S were obtained, respectively +1,88 % - + 6, 25 %o, which correspond to the values of sulfides of orogenic gold deposits (S³⁴S_H2 - -3.0 % - +9.0 %). The fluid that deposited antimonite at a temperature of 185 °C is characterized by the values of S³⁴S = S³⁴S = -0.5...+1.5 %, which indicates the proximity of the mantle source to sulfur. It is established that the ores of the quartz-antimonite association are characterized by high values of U / Th ratios (U/Th -1.92-5.50), indicating the reducing environment of their formation. The ores of quartz-polymetallic and quartz-arsenopyrite associations were formed in an oxidation-neutral environment (U/Th-0.34-0.97). The distribution of rare earth elements (REE) shows that the gold-bearing sulfide-quartz ores of the deposit are formed from magmatic foci of different depths to varying degrees of differentiation. During the ore process, the amount of REE decreases from the early stages to the late stages. The spatial and temporal relationship of their mineralization with the rocks of the Amudjikan dike complex (J2-3), as well as the isotopic ratios of oxygen in ore-bearing quartz veins and sulfur in sulfides, indicating magmatic sources of mineralization. The question of the relationship of quartz-antimonite mineralization with magmatism is less defined.

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