Conditions of gold mineralization formation in mineralized zones of the Yagodnoye ore occurrence based on chlorite geothermometry (Manitanyrd Ridge, Polar Urals)

The gold-bearing zone of the Yagodnoye ore occurrence was studied to determine the nature of metasomatic alterations in the host rocks, the chemical composition of chlorite, and the conditions of its formation. Metasomatites exhibit mineralogical and textural-structural characteristics typical of propylites from the epidote-chlorite subfacies. Petrographic analysis was conducted by Nikon Eclipse LV 100 ND optical microscope, while chlorite composition was determined via Tescan Vega 3 LMH scanning electron microscope equipped with an Oxford Instruments X-Max energy-dispersive spectrometer. The chemical composition of the studied chlorite corresponds to clinochlore. The temperature of mineral formation was estimated by a chlorite geothermometer. Clinochlore (pycnochlorite), associated with gold-bearing pyrite metacrystals, formed at 306–235 °C. Clinochlore (pennine) is found only in the form of single inclusions in pyrite, is significantly enriched in Si, and its formation temperature is 185–157 °C. The paragenetic association of chlorite with gold-bearing pyrite metacrysts suggests that both minerals were co-precipitated simultaneously during a single metasomatic process at 306–157 °C with a peak temperature of 306–235 °C.