Gold-tourmaline mineralization in carbonaceous shales of the Kumak deposit (South Ural)

Abstract

The article discusses the geological structure of the Kumak gold ore deposit, confined to the Early Carboniferous Anikhov graben of the East Ural uplift. It is composed of sericite-quartz-carbon and quartz-carbon-tourmaline schists of the Bredy Formation (C1bd). Black shale deposits are carbonaceous type and belong to terrigenous-carbonaceous and silicon-carbonaceous formations. Among the main minerals in shales are noted: quartz, sericite, carbonates, sulfides, tourmaline and carbonaceous matter. The field is characterized by a wide variety of gold ore mineralization. Rich ore zones are noted at the intersection of the East Anikhov faults oriented in the north–south direction and the branching tensile fractures in the north-north-east and north-west directions. In the ore mineral association prevailing here, finely dispersed gold is associated with small crystals of pyrite, arsenopyrite and concentrates nearby abundant tourmaline areas. The fine intergrowth of tourmaline and gold indicates the synchronism of their formation and allows us to distinguish a quartz-tourmaline gold ore formation within the Kumak deposit, comparable with a number of objects in East Transbaikal and Tuva. The most probable source of tourmaline mineralization in sericite-quartz-carbon schists could be metamorphically transformed boron-containing marine sediments saturated with clay particles and Corg. The microprobe study of gold grains taken from carbonaceous shales and weathering crusts made it possible to attribute them to the high-grade (919–1000) type, which is the leading one in the gold ore mineralization of the considered deposit. It is established that in the zone of hypergenesis, gold grains are not homogeneous. Here, secondary redeposition of gold takes place in the form of small spongy high-grade aggregates, as well as the formation of a rim on some grains with clear signs of refinement and purification from impurity elements. The geological works were carried out under State Contract No. 0246-2019-0078. The analyses were supported by the regional Grant for Science and R&D, Agreement No. 23 dated August 18, 2019. The studies into gold composition were executed in the framework of state-financed scientific topic No. AAAA-A19-119072390050-9. The authors express thanks to S. A. Yagudin for the analysis implementation and to E. O. Kalistratov for the help in description of polished sections. Further thanks are extended to R. S. Kisil and V. S. Panteleev for the help in the field works.

Rare-earth minerals in carbonaceous shale of the Kumak gold deposit, South Urals, Russia

“…1). The volcanic sedimentary rocks are cut with numerous intrusive rocks from the Dzhabygasai diorite-plagiogranite-gabbro (pȖ-Ȗį-ȞD 3 d) and Kumak diorite-plagiogranite (įС 1 k) systems [13,17,18].…”

Geology and gold content of carbonaceous shale in Baikal mineralization site, Southern Ural

“…The alteration represents sericite ribbons, recrystallization and segregation of quartz into different thickness veins and strings, tourmalinization, development of carbonate and ferruginization. Rich ore zones are traced at the intersections of the N-S Eastern Anikhovsky Faults and branching disturbed fractures of the N-E and N-W orientation [14].…”

“…Here, a score or two gold ore deposits were discovered (East Tykasha, Kommercheskoe, Zabaikal, Baikal, Tsentralnoe, Kumak, Kumak South, etc.). Numerous exploration and geological studies accomplished in this area within nearly a century enabled adjustment of the ore field geology, as well as the metallogeny imaging and reconstruction of deposition of sediments [7,[11][12][13][14].…”

The Geology of Carbonaceous Deposits (Carboniferous) of the South Urals (Fedorovskaya Sequence, Sukharysh Syncline)

“…Earlier exploration campaigns have found that the Carboniferous carbonaceous shales of the East Urals megazone host a number of commercial gold deposits (Kumakskoe, Svetlinskoe, Kamenskoe, Tetechnoe, etc. ), thereby fostering greater research interest in this region [1][2][3][4][5].…”