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

Snachev A. V., Head of Laboratory, Candidate of Geological and Mineralogical Sciences, SAVant@rambler.ru
Panteleeva A. V., Researcher, Candidate of Geological and Mineralogical Sciences

South Ural Federal Research Center for Mineralogy and Geoecology, Ural Branch, Russian Academy of Sciences, Miass, Russia
Rassomahin M. A., Junior Researcher

The article presents the results of the study of carbonaceous shales from the Kumak deposit. The analysis of their geochemical features reveals their shallow water–near shore sedimentation conditions. The high-aluminous terrigenous sedimentary material underwent minimal transport and was formed mainly due to destruction of basic rocks. The sediments experienced a high degree of weathering typical of humid climates and deposited under conditions of oxidation and pre-oxidation. It is found that rare-earth elements (REE) practically do not accumulate in carbonaceous shales; their contents are correlated directly with the amount of terrigenous admixture, Normalization with respect to Post-Archean Australian shales (PAAS) shows that REE contents are in the range from 0.1 to 1 units. The carbonaceous shales are characterized by uniform normalized curves—preferential accumulation of light REE as against heavy REE, with a distinct europium minimum in a number of samples. The main minerals-concentrators for light REE are Monazite-(Ce) and Rhabdophane-(Ce), and for heavy REE—Xenotime-(Y). Xenotime is an yttrium mineral, with the content of Y₂O₃ up to 47.61 wt.%. Among the other REE which regularly replace yttrium, dysprosium, gadolinium and erbium prevail. Monazite is a cerium mineral, with the content of Ce₂O₃ up to 37.07 wt.%. The ratio of Ce₂O₃ to the sum of the other light REEs is stable and equals 1. In contrast to xenotime, monazite contains a significant thorium admixture reaching 13.32 wt.% of ThO2. Georceixite, bastnasite and pietersite-(Ce), which is an agardite-(Се) mineral, are represented by single grains. A large number of Th–REE compounds of complex composition and an unidentified As-Ce mineral in zircon are also observed.

The study was supported by the Russian Science Foundation, Grant No. 23-27-00265, https://rscf.ru/en/project/23-27-00265/.

1. Arifulov Ch. Kh. Black shales gold deposits of various geological conditions. Rudy i Metally. 2005. No. 2. pp. 9–19.
2. Gadd M. G., Peter J. M., Jackson S. E., Zhaoping Yang, Petts D. Platinum, Pd, Mo, Au and Re deportment in hyper-enriched black shale Ni-Zn-Mo-PGE mineralization, Peel River, Yukon, Canada. Ore Geology Reviews. 2019.
Vol. 107. pp. 600–614.
3. Groves D. I., Goldfarb R. J., Robert F., Hart C. J. R. Gold deposits in metamorphic belts: Overview of current understanding, outstanding problems, future research, and exploration significance. Economic Geology. 2003. Vol. 98, No. 1. pp. 1–29.
4. Ivanov A. I. The role played by metamorphic transformation conditions of carbonaceous carbonate–terrigenous deposits for gold mineralization formation at various stages of collisional epoch of Baikal-patom metallogenic province development. Otechestvennaya geologiya. 2017. No. 4. pp. 3–23.
5. Ketris M. P., Yudovich Ya. E. Estimation of clarkes for carbonaceous biolithes: World averages for trace elements contents in black shales and coals. International Journal of Coal Geology. 2009. Vol. 78, No. 2. pp. 135–148.
6. Large R. R., Bull S. W., Maslennikov V. V. A carbonaceous sedimentary source-rock model for Carlin type and orogenic gold deposits. Economic Geology. 2011. Vol. 106, No. 3. pp. 331–358.
7. Shumilova T. G., Shevchuk S. S., Isayenko S. I. Metal concentrations and carbonaceous matter in the black shale type rocks of the Urals. Doklady Earth Sciences. 2016. Vol. 469, No. 1. pp. 695–698.
8. Snachev A. V., Puchkov V. N. First findings of palladium–gold–REE ore mineralization in Precambrian carbonaceous shales on the western slope of the Southern Urals. Doklady Earth Sciences. 2010. Vol. 433, No. 1.
pp. 866–869.
9. Vysotsky S. I., Kovalev S. G. Geochemistry of rare-earth elements and noble metals in rock of the Shatak complex (South Urals). Geologicheskii vestnik. 2019. No. 2. рр. 58–71.
10. Xu L., Lehmann B., Mao J. Seawater contribution to polymetallic Ni-Mo-PGE-Au mineralization in Early Cambrian black shales of South China: Evidence from Mo isotope, PGE, trace element, and REE geochemistry. Ore Geology Reviews. 2013. Vol. 52. рр. 66–84.
11. Albov M. N. Secondary zoning of gold deposits in the Urals. Moscow : Gosgeoltekhizdat, 1960. 215 р.
12. Bilibina T. V., Bogdanov Yu. V. On the prospects of gold potential in the Mugodzhar region. Geologiya rudnykh mestorozhdeniy. 1959. No. 5. рр. 104–111.
13. Sazonov V. N., Koroteev V. A., Ogorodnikov V. N., Polenov Yu. A., Velikanov A. Ya. Gold in “black shales” of the Urals. Litosfera. 2011. No. 4. pp. 70–92.
14. Voin M. I. Features of structure and mineralization in the Kumak ore field and the detection procedure of rich pay zones in crushed veins. Izvestiya vuzov. Geologiya i razvedka. 1966. No. 11. pp. 77–86.
15. Kolomoets A. V., Snachev A. V. Geology and petrogeochemical features of the Kumak ore field carbonaceous shales. Processes in GeoMedia. 2021. Vol. 3. pp. 25–35.

16. Lyadskiy P. V., Chen-Len-Son B. I., Kvasnyuk L. N., Alekseeva G. A., Olenitsa T. V. et al. State geological map of the Russian Federation. Scale 1:200 000. 2^nd Edition. Series South Ural. Sheet M-41-VII(XIII) (Svetly). Explanatory note. Moscow MF FGBU VSEGEI, 2018. 128 p.
17. Kolomoets A. V., Snachev A. V., Rassomakhin M. A. Gold–tourmaline mineralization in carbonaceous shales of the Kumak deposit (South Ural). Gornyi Zhurnal. 2020. No. 12. pp. 11–15.
18. Snachev A. V., Kolomoets A. V., Rassomakhin M. A., Snachev V. I. Geology and gold content of carbonaceous shale in Baikal mineralization site, Southern Ural. Eurasian Mining. 2021. No. 1. pp. 8–13.
19. Yudovich Ya. E., Ketris M. P. Geochemistry of black shales. Moscow. Berlin: Direct Media, 2015. 272 p.
20. Nesbitt H. W., Young G. M. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature. 1982. Vol. 299. pp. 715–717.
21. Herron M. M. Geochemical classification of terrigenous sands and shales from core or log data. Journal of Sedimentary Petrology. 1988. Vol. 58. pp. 820–829.
22. Cullers R. L. Implications of elemental concentrations for provenance, redox conditions, and metamorphic studies of shales and limestones near Pueblo, CO, USA. Chemical Geology. 2002. Vol. 191, No. 4. pp. 305–327.
23. Roser B. P., Korsch R. J. Provenance signatures of sandstone–mudstone suites determined using discriminant function analysis of major-element data. Chemical Geology. 1988. Vol. 67, Iss. 1–2. pp. 119–139.
24. Jones B., Manning D. Comparison of geochemical indices used for the interpretation of paleoredox conditions in ancient mudstones. Chemical Geology. 1994. Vol. 111, Iss. 1–4. pp. 111–129.
25. Kholodov V. N., Naumov R. I. On the geochemical criteria for the appearance of hydrogen sulfide contamination in the waters of ancient reservoirs. Proceedings of the Academy of Sciences of the USSR. Geology series. 1991. Vol. 12. pp. 74–82.
26. Taylor S. R., Mc Lennan S. M. The Continental Crust: Its Composition and Evolution. Blackwell : Oxford, UK, 1985. 312 p.
27. Wakita H., Rey P., Schmitt R. A. Abundances of the 14 rare-earth elements and 12 other trace elements in Apollo 12 samples: fife igneous and one breccia rocks and four soils. Proceedings of the 2nd Lunar Science Conference. Oxford : Pergamon Press. 1971. рр. 1319–1329.
28. Cherepanov A. A., Berdnikov N. V., Shtareva A. V. Rare-earth elements and noble metals in phosphorites of the Gremuchy Occurrence, Lesser Khingan, Far East of Russia. Russian Journal of Pacific Geology. 2019. Vol. 13, No. 6. рр. 585–593.
29. Cherepanov A. A., Berdnikov N. V., Shtareva A. V., Krutikova V. O. Formation conditions and rare-earth mineralization of Riphean Carbonaceous shales of the Upper Nyatygran subformation, Russian Far East. Russian Journal of Pacific Geology. 2017. Vol. 11, No. 4. рр. 297–307.
30. Paikaray S., Banerjee S., Mukherji S. Geochemistry of shales from the Paleoproterozoic to Neoproterozoic Vindhyan Supergroup: Implications on provenance, tectonics and paleoweathering. Journal of Asian Earth Sciences. 2008. Vol. 32, Iss. 1. pp. 34–48.
31. Palenova E. E., Rozhkova E. A., Belogub E. V., Rassomakhin M. A. MREE minerals in black shales of the Paleoproterozoic Mikhailovka formation (Baikal-Patom highland, Siberia). Mineralogy. 2022. Vol. 8, No. 3. рр. 47–66.
32. Zanin Yu. N., Zamirailova A. G., Eder V. G., Krasavchikov V. O. Rare-earth elements in the Bazhenov formation of the West-Siberian sedimentary basin. Lithosphere. 2011. No. 6. pp. 38–54.
33. Warr L. IMA–CNMNC approved mineral symbols. Mineralogical Magazine. 2021. Vol. 85, Iss. 3. pp. 291–320.
34. Kovalev S. G., Maslov A. V., Kovalev S. S. Mineralogical and geochemical aspects of rare-earth elements behavior during metamorphism (on the example of the Upper Precambrian structural-material complexes of the Bashkir megaanticlinorium, South Urals). Georesources. 2020. Vol. 22, No. 2. pp. 56–66.