| Abstrakt: |
The Khangalas orogenic gold deposit is located in the central part of the Yana–Kolyma metallogenic belt. The structure of the deposit is defined by several mineralized fracturing zones up to 70 m thick and up to 1400 m long in the arch and the southwestern limb of a NW-trending anticline. The Upper Permian terrigenous rocks host ore bodies with massive, banded, veinlet, disseminated, and brecciated textures. The major gangue minerals include quartz, carbonates, and rare sericite. The major ore minerals are pyrite and arsenopyrite, the subordinate minerals are galena, sphalerite, chalcopyrite, and native gold, and Fe-gersdorffite, tetrahedrite, and argentotennantite are rare minerals. Supergene minerals (sulfates, phosphates, arsenates, and hydrooxides) are abundant in a linear oxidation zone. The mineral formation occurred in two stages: gold–sulfide–quartz and silver–quartz. Quartz veins with visible native gold formed from low-saline (~5.0 wt % NaCl-equiv.) CO2-bearing hydrocarbonate fluids at a temperature of 330–280°C and a pressure of ~0.8 kbar. Disseminated Au-bearing pyrite-3 (up to 39.3 ppm Au) and arsenopyrite-1 (up to 23.8 ppm Au) from sericite–carbonate–quartz metasomatites are characterized by nonstoichiometric composition, a Fe excess, and a deficit of S (in addition to As in Apy), and Fe/(S + As) ratios of 0.47–0.52 (Py2) and 0.47–0.50 (Apy 1). Structurally bound Au+ is the dominant mode of occurrence of invisible gold in Py3 and Apy1. The isotopic composition of oxygen of quartz (+15.2 to +16.1‰ δ18O) and fluid (+8.4 to +9.2‰ δ18OH2O), as well as sulfur of sulfides (–2.1 to 0.6‰ δ34S), in addition to the 187Os/188Os ratios (0.2212–0.2338) of native gold and Pb of galena (206Pb/204Pb = 18.0214, 207Pb/204Pb = 15.5356, and 208Pb/204Pb = 38.2216) and geochemical features of Py3 and Apy1, allow us to suggest that sources are involved in ore formation that are mainly from the subcontinental lithospheric mantle and, to a lesser extent, crustal reservoirs. The formation of gold-bearing ore bodies of the deposit is related to the final progressive reverse-thrust deformations of stage D1 of the Valanginian period of the Early Cretaceous (~137 Ma), which occurred during postorogenic processes in the Yana–Kolyma belt upon regional southwestern transportation of rocks. Our results are important for forecasting metallogenic and prospecting works directed for the discovery of large-volume gold mineralization of orogenic belts. [ABSTRACT FROM AUTHOR] |
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