Based on ICP-MS, optical and electron microscopy, and electron back-scatter diffraction data, the paper considers the distribution and mode of occurrence of REE and Th in metasandstones of the Lower Proterozoic Sakukan Formation, which host mineralization of the Udokan and Unkur copper sandstone deposits. The REE and Th contents increase in the layers enriched in iron oxides and minerals of natural heavy concentrate relatively to the background metasandstones. Detrital allanite is the major REE mineral, which occurs in layers enriched in iron oxides together with authigenic allanite, monazite, and unidentifed Ca and REE carbonates. Thorium is concentrated in an authigenic silicate (thorite or thorogummite), which contains a signifcant amount of Fe, Ca, Al, and Cu and microinclusions of Cu and Pb sulfdes and barite. The diagenetic formation of authigenic REE and Th minerals is suggested as a result of desorption of these elements from siliceous-ferruginous gel-like sediments formed in river deltas and the wave-cut zone of the Proterozoic Sea.
Keywords: Udokan, Unkur, rare earth elements, thorium, sedimentary rocks.

Received 01.06.2022, accepted 07.06.2022

E.V. Belogub, South Urals Federal Research Center of Mineralogy and Geoecology UB RAS, Institute of Mineralogy, Miass, Chelyabinsk Region, 456317 Russia; belogub@mineralogy.ru

K.A. Novoselov, South Urals Federal Research Center of Mineralogy and Geoecology UB RAS, Institute of Mineralogy, Miass, Chelyabinsk Region, 456317 Russia;

V.V. Shilovskikh, St. Petersburg State University, Resource Center «Geomodel», ul. Ul’yanovskaya 1, Petergof, St. Petersburg, 198504 Russia

I.A. Blinov, South Urals Federal Research Center of Mineralogy and Geoecology UB RAS, Institute of Mineralogy, Miass, Chelyabinsk Region, 456317 Russia;

E.E. Palenova, South Urals Federal Research Center of Mineralogy and Geoecology UB RAS, Institute of Mineralogy, Miass, Chelyabinsk Region, 456317 Russia

1. Abramov B.N. (2004) [Precious metals in sedimentary-metamorphic rocks and intrusive rock complexes of the Kodar-Udokan zone]. Geokhimiya [Geochemistry], 395(2), 224–226. (in Russian)
2. Abramov B.N. (2006) [Features of distribution of precious metals in copper sandstones of the Kodar-Udokan ore region]. Litosfera [Lithosphere], (4), 168–174. (in Russian)
3. Arkhangel’skaya V.V., Bykov Yu.V., Volodin R.N. et al. (2004) [Udokan copper and Katugino rare metals deposits in Chita district of Russia]. Chita, Ministerstvo prirodnykh resursov Rossii, 520 p. (in Russian)
4. Balashov Yu.A. (1976) [Geochemistry of rare earth elements]. Moscow, Nedra, 267 p. (in Russian)
5. Belogub E.V., Shilovskikh V.V., Novoselov K.A.(2018) [REE minerals of phyllites of the Main Central Thrust of the Tamor window area, Eastern Nepal]. Mineralogiya [Mineralogy], 4(3), 70–81. (in Russian)
6. Belogub E.V., Shilovskikh V.V., Novoselov K.A., Blinov I.A., Filippova K.A. (2021) Authigenic rhabdophane from brown iron ore of the oxidation zone of the Babaryk massive sulfde occurrence (South Urals): scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) study. European Journal of Mineralogy, 33(5), 605–620.
7. Berezhnaya N.G., Bibikova E.V., Sochava A.V., Kirnozova T.I., Makarov V.A., Bogomolov E.S. (1988) [Isotope age of China subseries of Udokan series of Kodar-Udokan defexion]. Doklady Akademii nauk SSSR [Doklady Academy of Science of the USSR], 302(5), 1209–1212. (in Russian)
8. Boswell A., Wing B.N., Ferry J.M., Harrison T.M.(2003) Prograde destruction and formation of monazite and allanite during contact and regional metamorphism of pelites: Petrology and geochronology. Contribution to Mineralogy and Petrology, 145, 228–250.
9. Brown A.C. (1997) World?class sediment?hosted stratiform copper deposits: Characteristics, genetic concepts and metallotects. Australian Journal of Earth Sciences, 44, 317–328
10. Bufeev Yu.V., Shsherbakova I.P. (1978). [Geological map of the USSR on a scale of 1:200 000 (O-50-XXXV). Explanation notes]. Leningrad, VSEGEI, 123 p. (in Russian)
11. Chechetkin V.S., Volodin R.N., Narkelyun L.F., Trubachev A.I., Bykov Yu.V., Markevich G.E. (1995) [Udokan copper sandstone deposit]. In: Mestorozhdeniya Zabaikal’ya [Deposits of Transbaikalia]. Moscow, Geoinformmark, 10–19. (in Russian)
12. Chechetkin V.S., Yurgenson G.A., Narkelyun L.F., Trubachev A.I., Salikhov V.S. (2000) [Geology and ores of the Udokan copper deposit: a review)]. Geologiya i geofzika [Geology and Geophysics], 41(5), 733–745. (in Russian)
13. Dinali G.S., Root R.A., Amistadi M.K., Chorover J., Lopes G., Guilherme L.R.G. (2019) Rare earth elements (REY) sorption on soils of contrasting mineralogy and texture. Environment International,128, 279–291.
14. Fedorovsky V.S. (1972) [Stratigraphy of the Lower Proterozoic of the Kodar and Udokan ranges]. Moscow, Nauka. 130 p. (in Russian)
15. Ferry J. M. (2000) Patterns of mineral occurrence in metamorphic rocks. American Mineralogist, 85, 1573–1588.
16. Gablina I.F., Malinovsky Yu.M. (2008) Periodicity of copper accumulation in the Earth’s sedimentary shell. Lithology and Mineral Resources, (2), 136–153.
17. Gamaletsos P.N., Godelitsas A., Filippidis A., Pontikes Y. (2019) The rare earth elements potential of GРЗЭk bauxite active mines in the light of a sustainable REE demand. Journal of Sustainable Metallurgy, (5), 20–47.
18. Gongalsky B.I. (2015) [Deposits of a unique metallogenic province of Northern Transbaikalia]. Moscow, VIMS, 248 p. (in Russian)
19. Hartmann B.T., Gaupp R., Oberhaensli R. (1997) Authigenic rare earth fuorocarbonates (synchiste) in Rotliegend sandstone from the North-German Basin: Constraints for РЗЭ mobility during diagenesis. Gaea Heidelberg, (3), 158.
20. Hitzman M., Kirkham R., Broughton D., Thorson J., Selley D. (2005) The Sediment-Hosted Stratiform Copper Ore System. Economic Geology 100th Anniversary Volume, 609–642.
21. Hitzman M., Selley D., Bull S. (2010) Formation of sedimentary rock-hosted stratiform copper deposits through Earth history. Economic Geology, 105, 627-639.
22. [Interpretation of geochemical data. Textbook] (2001). Ed. E.V. Sklyarov. Moscow, Intermet Engineering, 288 p. (in Russian)
23. Kohn M.J., Malloy A.M. (2004) Formation of monazite via prograde metamorphic reactionsamong common silicates: implications for age determinations. Geochimica et Cosmochimica Acta, 68, 101–113.
24. Lazareva E.V., Zhmodik S.M., Dobretsov N.L., Tolstov A.V., Shcherbov B.L., Karmanov N.S., Gerasimov E.Yu., Bryanskaya A.V. (2015) Main minerals of abnormally high-grade ores of the Tomtor deposit (Arctic Siberia). Russian Geology and Geophysics, 56(6), 844–873.
25. Leybourne M.I., Peter J.M., Layton-Matthews D., Volesky J., .Boyle D.R. (2006) Mobility and fractionation of rare earth elements during supergene weathering and gossan formation and chemical modifcation of massive sulfde gossan. Geochimica et Cosmochimica Acta, 70, 1097–1112.
26. Lur’e A.M. (1988) [Genesis of copper sandstones]. Moscow, Nauka. 182 p. (in Russian)
27. Makeev A.B., Borisovskii S.E., Krasotkina A.O.(2020) [Chemical composition and age of monazite and kularite from titanium ores of Pizhem and Yarug deposits (Central and South Timan)]. Georesursy [Georesources], 22(1), 22–31. (in Russian)
28. Marino E., Gonzalez F.J., Kuhn T., Madureira P., Wegorzewski A.V., Mirao, J. Medialdea T., Oeser M., Miguel C., Reyes J. (2019) Hydrogenetic, diagenetic and hydrothermal processes forming ferromanganese crusts in the Canary island seamounts and their infuence in the metal recovery rate with hydrometallurgical methods. Minerals, (9), 439.
29. Nemerov V.K., Budyak A.E., Razvozzhaeva E.A., Makrygina V.A., Spiridonov A.M. (2009) [A new glance on the origin of copper sandstones from the Udokan deposit]. Izvestiya Sibirskogo otdeleniya Sektsii nauk o Zemle RAEN. [Proceedings of the Siberian Branch of Section of the Earth Sciences of the Russian Academy of Natural Sciences], 2(35), 4–17. (in Russian)
30. Novoselov K.A., Belogub E.V., Kotlyarov V.A., Schilovskikh V.V. (2017) [Betekhtinite from the Udokan sandstone-hosted copper deposit (Transbaikalia, Russia)]. Mineralogiya [Mineralogy], (2), 14–21. (in Russian)
31. Novoselov K., Belogub E., Palenova E., Blinov I.(2020) Silver minerals in the Unkur sandstone-hosted Cu deposit (Transbaikalia region, Russia). Neues Jahrbuch fur Mineralogie – Abhandlungen, 196(3), 221–230.
32. Perello J., Sillitoe R., Yakubchuk A., Valencia V., Comejo P. (2017) Age and tectonic setting of the Udokan sediment-hosted copper-silver deposit, Transbaikalia, Russia. Ore Geology Reviews, 86, 856–866.
33. Piilonen P.C., Rowe R., Poirier G., Grice J.D., McDonald A.M. (2014) Discreditation of Thorogummite. The Canadian Mineralogist, 52, 769–774.
34. Podkovyrov V.N., Kotov A.B., Larin A.M., Koto-va L.N., Kovach V.P., Zagornaya N.Yu. (2006) Sources and provenances of the Lower Proterozoic terrigenous rocks of the Udokan Group, Southern Kodaro-Udokan depression: results of Sm-Nd isotopic investigations. Doklady Earth Sciences, 408, 518–522.
35. Pokrovsky B.G., Grigoriev V.S. (1995) [New data on the age and geochemistry of isotopes of the Udokan Group, Lower Proterozoic of Eastern Siberia]. Litologiya i poleznye iskopaemye [Lithology and Mineral Resources], (3), 273– 283. (in Russian)
36. Rasmussen B., Buick R., Wayne R., Taylor C. (1998) Removal of oceanic REE by authigenic precipitation of phosphatic minerals. Earth and Planetary Science Letters, 164, 135–149.
37. Shepel E.V., Ayupova N.R., Rassomakhin M.A., Khvorov P.V. (2021) [Thorium, uranium and rare earth mineralization in rocks of the Ugakhan gold deposit, Bodaibo ore region]. Mineralogiya [Mineralogy], 7(3), 78–93. (in Russian)
38. Sokol E., Kokh S., Kozmenko O., Nekipelova A., Rudmin M., Khvorov P., Artemyev D. (2020) Geochemistry and mineralogy of rare earth elements in high-phosphorus ooidal ironstones: A case study of the Kamysh-Burun deposit (Azov–Black Sea iron Province). Ore Geology Reviews, 127, 103827.
39. Taylor S.R., McLennan S.M. (1985) The continental crust: its evolution and composition. Oxford, Blackwell Scientifc Publications. 1985, 312 p.
40. Turekian K., Wedepohl K. (1961) Distribution of the elements in some major units of the Earth’s crust. Geological Society of America Bulletin, 72, 175–192.
41. Volkova M.G., Budyak A.E., Nevol’ko P.A., Bryukhanova N.N., Spiridonov A.M. (2012) [Relationship of black shale strata with ore formation processes within the Kodar-Udokan lithostructural zone]. Izvestiya SO RAN Sektsii nauk o Zemle RAEN. Geologiya, poiski i razvedka rudnykh mestorozhdeniy [Proceeding of SB RAS of Section of the Earth Sciences of the Russian Academy of Natural Sciences. Geology, Prospecting and Exploration of Ore Deposits], 41(2), 54–68. (in Russian)
42. Volodin R.N., Savchenko A.A., Fedotova V.M., Kichigin A.I. (1982) [Elaboration of criteria for predicting of occurrences of copper mineralization in the Udokan ore district to substantiate the direction of geological exploration. Report on topic 41-1/5 in 2 volumes]. Moscow, TsNIGRI. (in Russian)
43. Yang J., Torres M., McManus J., Algeo T.J., Hakala J.A., Verba C. (2017) Controls on rare earth element distributions in ancient organic-rich sedimentary sequences: role of post-depositional diagenesis of phosphorus phases. Chemical Geology, 466, 533–544.
44. Yurgenson G.A., Abramov B.N. (2000) [Mineral composition of ferruginous sandstones and sources of clastic material of copper-bearing sediments of the Udokan Group]. Zapiski Rossiiskogo mineralogicheskogo obshchestva [Proceedings of the Russian Mineralogical Society], 129 (2), 44–53. (in Russian)
45. Zientek M., Chechetkin V., Parks H., Box S., Briggs D., Cossette P., Dolgopolova A., Hayes T., Seltmann R., Syusyura B., Taylor C., Wintzer N. (2014) Assessment of undiscovered sandstone copper deposits of the Kodar-Udokan area, Russia: Chapter M in Global mineral resource assessment. 134 p.