On the mineralogy of the Ukonik gold deposit in Transbaikalia (Russia)

As a result of studying new ore samples from the Ukonik deposit, new data on the composition of pyrite was obtained, the composition of electrum was studied for the first time and plattnerite, hessite, jalpaite, silver-bearing covellite and greigite were identified, and the sequence of their formation was determined. It was determined that a significant part of the pyrite (48%) contains arsenic in the amount of 0.82 - 2.28 wt.%, which is typical for the upper parts of many gold deposits. This is also evidenced by an insignificant admixture of cobalt (0.5 – 0.55 wt.%) in only two samples. The bulk of gold in the ore is associated with electrum, containing from 41.26 to 63.11 wt.% gold. Mercury electrum was found to contain up to 3.29 wt.% Hg. For the first time in Transbaikalia, plattnerite, which usually belongs to the minerals of the supergenesis zone, has been identified and studied in the ores of the upper part of the Ukonik deposit. In this case, it is one of the last products of the evolution of the hydrothermal mineral-forming system, preceding the formation of dolomite. Hessite containing variable amounts of copper, lead and antimony was discovered for the first time. This hessite-like telluride is of interest for further research.