Institute of Geology, Ufa Federal Research Center, Russian Academy of Sciences, Ufa, Russia:

Snachev A. V., Head of Laboratory, Candidate of Geologo-Mineralogical Sciences, SAVant@rambler.ru

Snachev V. I., Professor, Doctor of Geologo-Mineralogical Sciences

Orenburg State University, Orenburg, Russia:
Kolomoets A. V., Senior Lecturer

South Urals Federal Research Center of Mineralogy and Geoecology, Russian Academy of Sciences, Miass, Russia:

Rassomakhin M. A., Junior Researcher

The authors analyze gold mineralization in Baikal site inside Kumak ore field, adjoined to Bredin black shale sediments (С1bd). It is found that the gold mineralization within the site adjoins mostly bands of quart–micaceous–tourmaline metasomatically altered carbonaceous shale. Float sampling of all local rock varieties shows commercial content of gold (to 6.5 g/t) and stable high content of silver (to 7.6 g/t). Gold is mostly finely dispersed, and is connected with two basic mineral associations: gold–bismuth–telluride and native gold intergrown with tourmaline. The analysis of compositions of gold particles reveals their high carat type. Chemically, tourmaline belongs to dravite and foitite, and is similar to tourmaline from the deposits of orogenic gold and goldbearing sulfide ores. Tight accretion of fine needle-like tourmaline and gold implies their synchronous formation, and allows assessing Baikal site as the quartz–tourmaline gold ore formation.

The study was carried out under State Contract Topic No. 0246-2019-0078, the microprobe analyses were performed under State-Financed Topic No. AAAA-A19-119072390050-9 and were supported by Orenburgneft JSC in the framework of a corporate grant, 2019–2020.
The authors are extremely grateful to S. A. Yagudina, T. I. Chernikova and I. V. Smoleva for the analysis execution, to E. O. Kalistratova for the help in heavy concentrate description, as well as to R. S. Kisil and V. S. Panteleev for the assistance in field works.

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