Black and gray nephrite of the Kavokta deposit, Middle-Vitim mountain country: properties and mineral composition
- 1Dobretsov Geological Institute of the Siberian Branch of the Russian Academy of Sciences, Ulan-Ude, Russian Federation
- 2Baikal Institute of Environmental Management SB RAS, Ulan-Ude, Russian Federation
Abstract
Relevance. The Kavokta deposit contains gray and black dolomite type nephrite, which is in high demand. Despite the fact that black nephrite has been found in several deposits, the reasons for its color are not well understood. Aim. To identify the localization and mineral composition of gray and black nephrite, and to determine the reasons for this color. Methods. The mineral composition of nephrite was studied using a scanning electron microscope with energy-dispersive microanalysis, X-ray phase analysis, and the isotopic composition of graphite carbon in nephrite and carbonates in the surrounding strata was determined. Results and conclusion. The gray to black color of most samples from the southeastern part of the Kavokta deposit (lodes 17 and 28 of the nephrite-bearing zone 4 of the Medvezhy section and lode 6-1 of the nephrite-bearing zone 6 of the Levoberezhny section) is due to the presence of graphite. Sigenetic graphite is formed both by the organic matter buried in dolomites and by the decomposition of carbon dioxide that appears during decarbonization under the effect of deep-seated hydrogen. The color of nephrite also depends on the iron content, changing from white to light green as the iron content increases. The gray color of tremolite-diopside nephrite is due to the development of chlorite aggregates that replace diopside and/or tremolite. The gray-green to black color of the nephrite in the northwestern part of the Kavokta deposit (lode 1 of the nephrite-bearing zone 1 of the Prozrachny section) is due to the high iron content in the tremolite to actinolite at the contact with the after amphibolite epidote-tremolite skarn. The identified patterns of black nephrite localization can be used in geological exploration.
For citation: Kislov E.V., Kotova I.Yu., Posokhov V.F., Trofimov A.V., Khromova E.A. Black and gray nephrite from the Kavokta deposit, Middle-Vitim mountain country: properties and mineral composition. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 10, pp. 226–241. http://doi.org/10.18799/24131830/2026/10/5319
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BibTeX
@article{kislov2026black,
title = {{Black and gray nephrite of the Kavokta deposit, Middle-Vitim mountain country: properties and mineral composition}},
author = {Evgeny V. Kislov and Irina Yu. Kotova and Viktor F. Posokhov and Artem V. Trofimov and Elena A. Khromova},
journal = {Известия Томского политехнического университета: Инжиниринг георесурсов},
year = {2026},
month = oct,
doi = {10.18799/24131830/2026/10/5319},
url = {https://doi.org/10.18799/24131830/2026/10/5319},
note = {CC BY-NC},
}
RIS
TY - JOUR
TI - Black and gray nephrite of the Kavokta deposit, Middle-Vitim mountain country: properties and mineral composition
AU - Evgeny V. Kislov
AU - Irina Yu. Kotova
AU - Viktor F. Posokhov
AU - Artem V. Trofimov
AU - Elena A. Khromova
PY - 2026
DA - 2026/10/31
JO - Известия Томского политехнического университета: Инжиниринг георесурсов
DO - 10.18799/24131830/2026/10/5319
UR - https://doi.org/10.18799/24131830/2026/10/5319
AB - Relevance. The Kavokta deposit contains gray and black dolomite type nephrite, which is in high demand. Despite the fact that black nephrite has been found in several deposits, the reasons for its color are not well understood. Aim. To identify the localization and mineral composition of gray and black nephrite, and to determine the reasons for this color. Methods. The mineral composition of nephrite was studied using a scanning electron microscope with energy-dispersive microanalysis, X-ray phase analysis, and the isotopic composition of graphite carbon in nephrite and carbonates in the surrounding strata was determined. Results and conclusion. The gray to black color of most samples from the southeastern part of the Kavokta deposit (lodes 17 and 28 of the nephrite-bearing zone 4 of the Medvezhy section and lode 6-1 of the nephrite-bearing zone 6 of the Levoberezhny section) is due to the presence of graphite. Sigenetic graphite is formed both by the organic matter buried in dolomites and by the decomposition of carbon dioxide that appears during decarbonization under the effect of deep-seated hydrogen. The color of nephrite also depends on the iron content, changing from white to light green as the iron content increases. The gray color of tremolite-diopside nephrite is due to the development of chlorite aggregates that replace diopside and/or tremolite. The gray-green to black color of the nephrite in the northwestern part of the Kavokta deposit (lode 1 of the nephrite-bearing zone 1 of the Prozrachny section) is due to the high iron content in the tremolite to actinolite at the contact with the after amphibolite epidote-tremolite skarn. The identified patterns of black nephrite localization can be used in geological exploration. For citation: Kislov E.V., Kotova I.Yu., Posokhov V.F., Trofimov A.V., Khromova E.A. Black and gray nephrite from the Kavokta deposit, Middle-Vitim mountain country: properties and mineral composition. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 10, pp. 226–241. http://doi.org/10.18799/24131830/2026/10/5319
SN - 2500-1019
SN - 2413-1830
ER -