The paper examines mineralogy of noble metals and ore formation conditions at the Naily gold deposit (South Urals), which is hosted in pyrite-bearing talc-carbonate, chlorite-quartz-carbonate and quartz-carbonate metasomatites after serpentinites and rocks of a gabbrodiorite-plagiogranite complex. Based on microscopic and electron microscopic studies of polished sections and heavy concentrates, it is established that native gold and Au tellurides are the major Au minerals of veins, metasomatites after intermediate and felsic intrusive rocks and foliated serpentinites. Native gold occurs as: 1) inclusions in pyrite and rarely in chalcopyrite, 2) free particles associated with non-metallic minerals, which probably fll interstitions, 3) interstitial forms in pyrite aggregates often together with chalcopyrite, galena and sphalerite, and veinlets in hessite, 4) fne inclusions in tetradymite and 5) inclusions in limonite. Tellurides of noble metals include calaverite, petzite, hessite and an unidentifed Ag and Pb sulfotelluride. Silver is also incorporated in acanthite and Hg-Ag-Sb-As, Pb-Bi-Ag and Cu-Ag-Pb-Bi sulfosalts. The Ag content of free native gold is 10–16 wt. % increasing to 20–24 wt. % in native gold in pyrite and in assemblage with hessite. Altaite, coloradoite and Ni and Pd tellurides are found in assemblages similar to noble metal mineralization. The formation temperature of chlorite from ore-bearing metasomatites is 339–392 °C. Fluid inclusions in quartz, calcite and albite are homogenized at a temperature range of 162–377 °C. The eutectic temperature (–23.5 °C) is typical of NaCl-KCl-H2O system. The ice melting temperature varies from –0.5 to –3.7 °C corresponding to salinity of 0.9– 6.0 wt. % NaCl-equiv.

Received 25.10.2024, revised 26.11.2024, accepted 01.12.2024

Keywords: Naily deposit, metasomatites, native gold, tellurides of noble metals, South Urals.

Funding. This work was supported by state contract of the South Urals Federal Research Center of Mineralogy and Geoecology UB RAS no. 075-00622-24-00.

Acknowledgments. The authors are grateful to N.K. Nikandrova for microthermometric work and E.D. Zenovich for X-ray structural analysis of rocks.

Confict of interest. The author declare that she has no conficts of interest.

Author contribution. A.D. Smirnitskaya – conceptualization, optical microscopic studies, writing the manuscript, visualization; E.A. Rozhkova – optical microscopic studies, writing the manuscript, visualization; E.V. Belogub – conceptualization, feld work, editing the fnal version of the manuscript; K.A. Novoselov – feld and optical microscopic work; M.V. Zabotina – feld, optical-microscopic work, mineralogical thermometry; M.A. Rassomakhin – analytical works. All the authors approved the fnal version of the manuscript prior to publication.

For citation: Smirnitskaya A.D., Rozhkova E.A., Belogub E.V., Novoselov K.A., Zabotina M.V., Rassomakhin M.A. Mineralogy and ore formation conditions of the Naily gold deposit (South Urals). Mineralogy, 2024, 10(4), 150–171. DOI: 10.35597/2313-545X-2024-10-4-7

A.D. Smirnitskaya, South Ural Federal Research Center of Mineralogy and Geoecology UB RAS, Miass, Chelyabinsk region, 456317 Russia; smirnitskaya@mineralogy.ru

E.A. Rozhkova, South Ural Federal Research Center of Mineralogy and Geoecology UB RAS, Miass, Chelyabinsk region, 456317 Russia;

E.V. Belogub, South Ural Federal Research Center of Mineralogy and Geoecology UB RAS, Miass, Chelyabinsk region, 456317 Russia;

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

M.V. Zabotina, South Ural Federal Research Center of Mineralogy and Geoecology UB RAS, Miass, Chelyabinsk region, 456317 Russia;

M.A. Rassomakhin, South Ural Federal Research Center of Mineralogy and Geoecology UB RAS, Miass, Chelyabinsk region, 456317 Russia

1. Arifulov Ch.Kh. (2001) Unpublished report on study of patterns of distribution and composition of gold-platinum potential in Miass and Nepryakhino ore regions to identify the complex ore objects for prospecting and evaluation works. Moscow, TsNIGRI, Chelyabinsk branch “TFGI for the Ural Federal District”, no. 10375. (in Russian)
2. Artemyev, D. A. Kraynev Yu. D., Zaikov V. V. (2014) Mineralogical and geochemical features of the Borisovslie zhily gold deposit (Miass region, South Urals). Metallogeniya drevnih i sovremennyh okeanov-2014. Dvadtzat let na peredovyh rubezhah geologii mestorozhdeniy poleznyh iskopaemyh (Metallogeny of Ancient and Modern Oceans. Twenty Years at the Frontiers of Geology of Mineral Deposits). Miass, IMin UrO RAN, 137–142. (in Russian)
3. Belogub E.V., Melekestseva I.Yu., Novoselov K.A., Zabotina M.V., Tret’yakov G.A., Zaykov V.V., Yuminov A.M. (2017) Listvenite-related gold deposits of the South Urals (Russia): A review. Ore Geology Reviews, 85, 147– 270. https://doi.org/10.1016/j.oregeorev.2016.11.008
4. Betekhtin A.G. (1950) Mineralogy. Moscow, Gosgeolizdat, 957 p. (in Russian)
5. Borisenko A.S. (1977) Study of salinity of fuid inclusions in minerals using cryometry. Geolofya i geofzika (Geology and Geophysics), 8, 16–28. (in Russian)
6. Cathelineau M. (1988) Cation site occupancy in chlorites and illites as a function of temperature. Clay Minerals. V. 23. P. 471–485.
7. Ermakov N.P., Dolgov Yu.A. (1979) Thermobarogeochemistry. Moscow, Nedra, 272 p. (in Russian)
8. Fedoseev V.V. (2011) Project for the implementation of «Prospecting and appraisal work in the Naily area for ore gold». JSC “UGC”. Plast, 128 p. (in Russian)
9. Fedoseev V.V., Ryabov Yu.I., Gadzhieva L.A. (2020) Revaluation of gold deposits of the Chelyabinsk region: the basis for the development of mineral base of AO YuGK. Izvestiya TulGu. Nauki o Zemle (Proceedings of the Tula State University. Sciences of Earth), 4, 547–560. (in Russian)
10. Garrels R.M., Christ Ch.L (1968) Solutions, minerals, equilibria. Moscow, Mir, 368 p. (in Russian)
11. Geological map of the Russian Federation on a scale of 1:1 000 000, sheet N-40(4) (2001). Ufa.
12. Groznetsky D.P. (1975) Unpublished report on prospecting and exploration works at the Naily and Tyelga gold ore deposits carried out by Miass group in 1971–1974. Miass, Glavzoloto, (in Russian)
13. Gusev A.I. (2013) Classifcation of mercury mineralization of the Altai krai. Uspekhi sovremennogo estestvoznaniya (Advances in current natural sciences), 6, 110–114. (in Russian)
14. Hey M.H. (1954) A new review of the chlorites. Mineralogical Magazine, 30, 277–292. https://doi. org/10.1180/minmag.1954.030.224.01
15. Jowett E.C. (1991) Fitting iron and magnesium into the hydrothermal chlorite geothermometer. Geological Association of Canada / TAC / SEG Annual Meeting. Toronto, Abstract 16, A62.
16. Kasatkin A.V., Belogub E.V., Kuznetsov A.M., Novoselov K.A., Skoda R., Nestola F., Rogov D.A. (2023) Bismuth minerals from Yugo-Konevo and Porokhovskoe tungsten deposits (South Urals). Mineralogiya (Mineralogy), 9(3), 26–49. (in Russian). https://doi.org/10.35597/2313-545X-2023-9-3-3
17. Kozin A.K., Stepanov S.Yu., Shilovskikh V. V. (2022) Morphological and chemical features of cinnabar from gold placers of Central and North Urals. Metallogeniya drevnih i sovremennyh okeanov-2022. Ot vestshestvennogo sostava k modelyam i prognosirovaniyu mestorozhdeniy (Metallogeny of Ancient and Modern Oceans. From Composition to Models and Forecasting the Deposits). Miass, YuU FNTs MiG UrO RAN, 113–117. (in Russian)
18. Kozin A.K., Stepanov S.Yu., Palamarchuk R.S., Shilovskikh V.V., Zhdanova V.S. (2023) Mineral associations of concentrates from gold-bearing placers of the Miass placer zone (South Urals) and possible primary sources of gold. Russian Geology and Geophysics, 64(9), 1015–1030. https://doi.org/10.2113/RGG20234543
19. Korekina M.A., Savichev A.N. (2023) Formation conditions and sources of fuids of deposits of hydrothermal-metamorphic-metasomatic and hydrothermal-metamorphic barren vein quartz (Central and South Urals). Vestnik Sankt-Peterburgskogo universiteta. Nauki o Zemle (Vestnik of St. Petersburg University. Earth Sciences), 68(2), 200–217. (in Russian) https://doi.org/10.21638/spbu07.2023.201
20. Kranidiotis P., MacLean W.H. (1987) Systematics of chlorite alteration at the Phelps Dodge massive sulfde deposit, Matagami, Quebec. Economic Geology, 82, 1898– 1911. https://doi.org/10.2113/gsecongeo.82.7.1898
21. Krasnova N.I., Petrov T.G. (1997) Genesis of mineral individuals and aggregates. St. Petersburg, Nevsky Kur’er, 228 p. (in Russian)
22. Lobanov D.A., Usenko S.P. (1974) Unpublished report on prospecting works for ore gold conducted by the Zolotogorsk group in 1972–1973 within the Altyn-Tash ore feld. Verkhnyaya Pyshma. (in Russian)
23. Methodic recommendations for the application of the Classifcation of reserves of the deposits and forecast resources of solid mineral deposits (2007) Moscow, FGU GKZ, approved on 06/05/2007, no. 37-r. (in Russian)
24. Murzin V.V., Krinov D.I., Bortnikov N.S., Sazonov V.N. (2001) Staging, PTX conditions of ore formation and mode of occurrence of gold in ores of the Mindyak deposit (South Urals). In: Ezhegodnik–2001 (Yearbook–2001). Yekaterinburg, IGG UrO RAN, 166–171. (in Russian)
25. Petrovskaya V.N. (1973) Native gold. Moscow, Nauka, 348 p. (in Russian)
26. Popova V.I. (2002) Gold deposits of the Miass valley. Metallogeniya drevnih i sovremennyh okeanov-2002. Formirovanie i osvoenie mestorozhdeniy v ofolitovyh zonah (Metallogeny of Ancient and Modern Oceans-2002. Formation and Exploration of Deposits in Ophiolite Zones). Miass, IMin UrO RAN, 98–106. (in Russian)
27. Redder E. (1987) Fluid inclusions in minerals. Moscow, Mir, vol. 1, 560 p. (in Russian)
28. Sazonov V.N., Ogorodnikov V.N., Koroteev V.A., Polenov Yu.A. (2001) Gold deposits of the Urals. Yekaterinburg, UGGGA, 622 p. (in Russian)
29. Sazonov V.N. (1998) Gold-producing metasomatic formations of mobile belts (geodynamic settings and RTX parameters of formation, prognostic value). Yekaterinburg, UGGGA, 181 p. (in Russian)
30. Sigov A.P. (1948) Gold deposits of the North Miass group In: 200 let zolotoy promyshlennosty Urala (200 years of the gold industry of the Urals). Sverdlovsk. UFAN SSSR, 296–304. (in Russian)
31. Zabotina M.V., Belogub E.V., Novoselov K.A., Palenova E.E., Martesheva A.V., Blinov I.A. (2014) Ore mineralogy and features of host rocks of Ganeevskoe listvenite gold deposit (Uchaly region, Republic of Bashkortostan). Izvestiya Sibirskogo otdeleniya RAEN.
32. Geologiya, poiski i razvedka rudnykh mestorozhdeniy (News of the Siberian Branch of the Russian Academy of Natural Sciences. Geology, Prospecting and Exploration of Ore Deposits), 3(46), 16–28. (in Russian)
33. Zabotina M.V. (2016) Mineralogy and conditions of formation of the Ganeevskoye gold deposit (Uchalinsky ore region) (Candidate dissertation). St. Petersburg, SPbGU, 135 p. (in Russian)
34. Znamensky S.E., Michurin S.V. (2013) Formation conditions of the Mindyak gold-sulfde deposit (South Urals): structural and isotopic-geochemical issues. Litosfera (Lithosphere), 4, 121–135. (in Russian)
35. Znamensky S.E. (2009) Structural formation conditions of collision gold deposits of the eastern slope of the South Urals. Ufa, Gilem, 348 p. (in Russian)