Mineral Associations of Quartz–sulfide Ores, Zun-Kholba Gold Deposit, Eastern Sayan

The paper presents the results of studying the mineral composition of the main quartz–sulfide ores of the Zun-Kholba gold-ore deposit, the largest gold deposit in Eastern Sayan. Three mineral ore types are distinguished: compact pyrite–pyrrhotite, quartz–carbonate–sulfide, and quartz–polymetallic. Native gold occurs as isolations in pyrite-2. It develops along fractures and crystal edges or deposits in association with other ore minerals such as chalcopyrite, sphalerite, and galena. Gold deposited at the quartz–carbonate–sulfide stage has grade varying from 634 to 926‰; at the polymetallic stage, 467–860‰; at the Bi-telluride stage, 327–693‰. In addition, the dependence of the composition of impurity mineral associations on ore-bearing rock complexes was revealed. The source of bismuth could be a lamprophyre dike, and nickel minerals appear in ores in the areas of development of listvenitized rocks, products of tectonometasomatic transformations of ultramafic rocks. In terms of mineral relationships, four ore associations are established: pyrite–pyrrhotite, quartz–carbonate–sulfide, quartz–polysulfide, and Bi-telluride corresponding to the pre-ore stage and three successive ore-formation stages.