Geology, Mineralogy, Geochemistry, and Formation Conditions of the Tukan Gold Deposit, Khudolaz Trough, South Urals

The mineralogy and geochemistry of rocks of the Tukan gold deposit (quartz veins, dolerite, gabbrodiorite) have been studied in depth. The deposit is one of numerous small gold–quartz locations in the Khudolaz trough of the West Magnitogorsk zone. The morphology and composition of native gold were studied using an Axioskop 40A optical microscope and Tescan Vega 3 and JEOL-6390LV scanning electron microscopes. The chemical composition of rocks was determined by the X-ray fluorescence (Carl Zeiss VRA-30) and atomic emission (Shimadzu ICPE-9000) analyses. Fluid inclusions were examined using a Linkam TMS-600 heating-freezing stage equipped with an Olympus BX51 optical microscope and the Link-System 32 DV-NC software. The composition vapor phase in fluid inclusions was determined by Raman spectroscopy (Horiba LabRam HR800 Evolution). Gold-bearing quartz veins and dolerites cutting the gabbrodiorite intrusion of the Khudolaz Complex are associated with near-meridional strike-slip faults. Native gold various in morphology is hosted in fractures in quartz veins and altered dolerites. The composition of gold is stable, with an average fineness of 871 ± 8.3‰. Fluid inclusion study in gold-bearing quartz revealed that gold was precipitated at a temperature no less than 186–230°С from fluid with a salinity of 4–8 wt % NaCl equiv. The presence of СО 2 , N 2 , and CH 4 was identified in the vapor phase of fluid inclusions. Dolerite and gabbrodiorite hosting gold-bearing veins contain sulfides (pyrite, pyrrhotite, chalcopyrite, pentlandite, violarite) and sulfoarsenides (cobaltite and its analogs), as well as minerals of Ag (hessite) and Pb (kuranakhite and phases similar in composition to minerals of the dugganite group and burckhardtite).