FIRST DATA ON THE AGE OF THE IRBA IRON ORE FIELD (EASTERN SAYAN): U-Pb (ID-TIMS) GEOCHRONOLOGICAL STUDIES OF GARNET

The results presented here concern the U-Pb (ID-TIMS) geochronological studies of garnet from ore-bearing skarns of the Granatovoe deposit (Irba ore field, Eastern Sayan). The studied garnet is represented by polychrome grains. It has been found that the studied garnet is similar in composition to andradite (98–100 %), though some of the parts of the marginal zones show the presence of a grossular component (no more than 5 %). On the boundary of the central zone composed of brown garnet and the periphery of the crystals, there is a zone made up of andradite-grossular garnet, where the aluminum content often exceeds the iron content. Polychrome zonation in garnets from magnetite skarns of the Granatovoe deposit reflects a complex combination of diffusion and infiltration metasomatism. High mobility of iron away from the contact in the early stages of skarn formation gave rise to primary brown andradite in the exoskarn zone. A subsequent increase in metasomatism intensity provided formation of high-aluminous garnet and its growth on early andradite. The granite-hosted molybdenite inclusions are a characteristic feature of the ore association and other iron ore deposits of the Eastern Sayan. Studies have been made of garnet fragments from concentrically zoned polychrome grains. It has been found that the central dark-colored zones of andradite composition are more enriched in uranium (25–29 ppm) than the outer light-colored zones which demonstrate a much lower uranium content (3.5 ppm) and a significant loss of radiogenic lead (Pb_c/Pb_t=0.67). A thermal effect on garnet during the late metasomatic processes caused diffusion of lead in the outer zones, while the U/Pb system remained almost unchanged in the central parts. The data obtained are the first "direct" age estimate of magnetite mineralization of the Irba ore field (503±6 Ma; MSWD=1.3). Age consistency between gabbroid volcanoplutonic complexes in other areas of the Altai-Sayan region suggests a simultaneous occurrence of the Early Paleozoic iron ore mineralization within the eastern segment of the Altai-Sayan folded region and gives grounds to recognize the iron-ore metallogenic epoch at the accretion-collision stage of the Altai-Sayan folded region development.

1. Berzin N.A., Kolman R.G., Dobretsov N.L., Zonenshain L.P., Syao Syuchan, Chang E.Z., 1994. Geodynamic Evolution of the Western Part of the Paleo-Asian Ocean. Russian Geology and Geophysics 35 (7–8), 8–28 (in Russian)

2. Berzin N.A., Kungurtsev L.V., 1996. Geodynamic Interpretation of Geological Complexes of the Altai-Sayan Region. Russian Geology and Geophysics 37 (1), 63–81 (in Russian)

3. Berzina A.N., Berzina A.P., Gimon V.O., 2016. Paleozoic-Mesozoic Porphyry Cu (Mo) and Mo (Cu) Deposits Within the Southern Margin of the Siberian Craton: Geochemistry, Geochronology, and Petrogenesis (A Review). Minerals 6 (4), 125. https://doi.org/10.3390/min6040125.

4. Berzina A.N., Berzina A.P., Gimon V.O., 2019. The Aksug Porphyry Cu-Mo Deposit (Northeastern Tuva): Chronology of Magmatism and Ore Formation Processes (U-Pb and Re-Os Isotope Data) and Metallogenic Implications. Russian Geology and Geophysics 60 (9), 1060–1075. https://doi.org/10.15372/RGG2019070.

5. Berzina A.N., Berzina A.P., Gimon V.O., 2021. The Aksug Porhyry Cu-Mo Ore-Magmatic System (Northeastern Tuva): Sources and Formation of Ore-Bearing Magma. Russian Geology and Geophysics 62 (4), 445–459. https://doi.org/10.2113/RGG20194115.

6. Bogatsky V.V., 1969. Metasomatic Magnetite Deposits of Southern Middle Siberia. In: Problems in Petrology and Metallogeny of the Western Border of the Siberian Platform. Krasnoyarsk Book Publishing House, Krasnoyarsk, p. 19–48 (in Russian)

7. Dymkin A.M., Mazurov M.P., Nikolaev S.M., 1975. Petrology and Specific Features of the Formation of Magnetite Deposits in the Irba Ore Field (Eastern Sayan). Novosibirsk, Nauka, 185 p. (in Russian)

8. Kalugin A.S., Kalugina T.S., Ivanov V.I., 1981. Iron Ore Deposits of Siberia. Novosibirsk, Nauka, 238 p. (in Russian)

9. Kryukov A.V., Shelkovnikov A.D., Volobuev M.I., 1982. New Absolute Age Determinations of Rocks in Some Areas of the Krasnoyarsk Krai (Information). In: Materials on Geology of the Krasnoyarsk Krai. Iss. 3. Western Siberia Geological Survey, Krasnoyarsk, p. 257–260 (in Russian)

10. Ludwig K.R., 1991. PbDat 1.21 for MS-DOS: A Computer Program for IBM-PC Compatibles for Processing Raw Pb-U-Th Isotope Data. Version 1.07. USGS Open File Report, 35 p.

11. Ludwig K.R., 2008. ISOPLOT 3.70. A Geochronological Toolkit for Microsoft Excel. User’s Manual. Berkeley Geochronology Center Special Publication 4, 76 p.

12. Mao J., Pirajno F., Lehmann B., Luo M., Berzina A., 2014. Distribution of Porphyry Deposits in the Eurasian Continent and Their Corresponding Tectonic Settings. Journal of Asian Earth Sciences 79, 576–584. https://doi.org/10.1016/j.jseaes.2013.09.002.

13. Mazurov M.P., 1970. Intrusive Magmatism, Metasomatism and Ore Mineralization in the Irba Ore Field (Eastern Sayan). In: Problems of Regional Geology and Petrography of Siberia and Geochemical and Geophysical Methods. Proceedings of the Conference of Young Scientists and Post-Graduates. Iss. 2. Nauka, Novosibirsk, p. 69–72 (in Russian)

14. Mihalasky J., Ludington S., Hammarstrom J.M., Alexeiev D.V., Frost T.P., Light T.D., Robinson G.R., Briggs D.A., Wallis J.C., Miller R.J., 2015. Porphyry Copper Assessment of the Central Asian Orogenic Belt and Eastern Tethysides – China, Mongolia, Russia, Pakistan, Kazakhstan, Tajikistan, and India. U.S. Geological Survey Scientific Investigations Report 2010-5090-X. Reston, USA, 106 p. https://doi.org/10.3133/sir20105090X.

15. Polyakov G.V., 1971. Paleozoic Magmatism and Ore Mineralization in Southern Middle Siberia. Nauka, Moscow, 309 p. (in Russian)

16. Porter T.M., 2016. The Geology, Structure and Mineralisation of the Oyu Tolgoi Porphyry Copper-Gold-Molybdenum Deposits, Mongolia: A Review. Geoscience Frontiers 7 (3), 375–407. https://doi.org/10.1016/j.gsf.2015.08.003.

17. Rudnev S.N., 2013. Early Paleozoic Granitoid Magmatism in the Altai-Sayan Folded Area and the Lake Zone in Western Mongolia. SB RAS Publishing House, Novosibirsk, 300 p. (in Russian)

18. Rudnev S.N., Babin G.A., Semenova D.V., Travin A.V., 2024. Evolution of Intrusive Magmatism in West Sayan. Russian Geology and Geophysics 65 (10), 1161–1176. https://doi.org/10.2113/RGG20244704.

19. Rudnev S.N., Borisov S.M., Babin G.A., Levchenkov O.A., Makeev A.F., Plotkina Yu.V., Serov P.A., Matukov D.I., 2008. Early Paleozoic Batholiths in the Northern Part of the Kuznetsk Alatau: Composition, Age, and Sources. Petrology 16 (4), 395–419. https://doi.org/10.1134/S086959110804005X.

20. Rudnev S.N., Kiseleva V.Y., Babin G.A., Kovach V.P., Serov P.A., 2013. The Early Stages of Island-Arc Plagiogranitoid Magmatism in Gornaya Shoriya and West Sayan. Russian Geology and Geophysics 54 (1), 20–33. https://doi.org/10.1016/j.rgg.2012.12.002.

21. Rudnev S.N., Vladimirov A.G., Kruk N.N., Ponomarchuck V.A., Babin G.A., Borisov S.M., 2004. Early Paleozoic Granitoid Batholiths of the Altai-Sayan Folded Region (Lateral-Temporal Zoning and Sources). Doklady Earth Sciences 396 (4), 492–495.

22. Seltmann R., Konopelko D., Biske G., Divaev F., Sergeev S., 2011. Hercynian Post-Collisional Magmatism in the Context of Paleozoic Magmatic Evolution of the Tien Shan Orogenic Belt. Journal of Asian Earth Sciences 42 (5), 821–838. https://doi.org/10.1016/j.jseaes.2010.08.016.

23. Seltmann R., Porter T.M., Pirajno F., 2014. Geodynamics and Metallogeny of the Central Eurasian Porphyry and Related Epithermal Mineral Systems: A Review. Journal of Asian Earth Sciences 79, 810–841. https://doi.org/10.1016Zj.jseaes.2013.03.030.

24. Shokalskii S.P., Babin G.A., Vladimirov A.G., Borisov S.M., Gusev N.I., Tokarev V.N., Zybin V.A., Dubskii V.S. et al., 2000. Correlation of Igneous and Metamorphic Complexes of the Western Part of the Altai-Sayan Folded Region. GEO, Novosibirsk, 188 p. (in Russian)

25. Sotnikov V.I., Ponomarchuk V.A., Shevchenko D.O., Berzina A.N., 2003. The Aksug Porphyry Cu-Mo Deposit in Northeastern Tuva: 40Ar/39Ar Geochronology and Sources of Matter. Russian Geology and Geophysics 44 (11), 1119–1132 (in Russian)

26. Sotnikov V.I., Ponomarchuk V.A., Shevchenko D.O., Berzina A.P., Berzina A.N., 2001. 40Ar/39Ar Geochronology of Magmatic and Metasomatic Events in the Sora Porphyry Cu-Mo Ore Cluster (Kuznetsk Alatau). Russian Geology and Geophysics 42 (5), 744–785.

27. Stacey J.S., Kramers J.D., 1975. Approximation of Terrestrial Lead Isotope Evolution by a Two-Stage Model. Earth and Planetary Science Letters 26 (2), 207–221. https://doi.org/10.1016/0012-821X(75)90088-6.

28. Steiger R.H., Jäger E., 1977. Subcommission on Geochronology: Convention on the Use of Decay Constants in Geo- and Cosmochronology. Earth and Planetary Science Letters 36 (3), 359–362. https://doi.org/10.1016/0012-821X(77)90060-7.

29. Stifeeva M.V., Salnikova E.B., Arzamastsev A.A., Kotov A.B., Grozdev V.Yu., 2020. Calcic Garnets as a Source of Information on the Age of Ultramafic Alkaline Intrusions in the Kola Magmatic Province. Petrology 28 (1), 62–72. https://doi.org/10.1134/S0869591120010063.

30. Stifeeva M.V., Salnikova E.B., Kotov A.B., Gritsenko Yu.D., 2024. The First Age Data of the Deposits of Kondomsky Iron Ore Field (Gornaya Shoriya): Results of U-Pb (ID-TIMS) Dating of Garnet. Doklady Earth Sciences 514 (2), 246–250 (in Russian) https://doi.org/10.31857/S2686739724020073.

31. Vakhrushev V.A., 1965. Mineralogy, Geochemistry and Genetic Groups of the Contact-Metasomatic Iron Ore Deposits in the Altai-Sayan Region. Nauka, Moscow, 292 p. (in Russian)

32. Vladimirov A.G., Gibsher A.S., Izokh A.E., Rudnev S.N., 1999. Early Paleozoic Granitoid Batholiths of Central Asia: Abundance, Sources, and Geodynamic Formation Conditions. Doklady Earth Sciences 369А, 1268–1271.

33. Vladimirov A.G., Kozlov M.S., Shokal’skii S.P., Khalilov V.A., Rudnev S.N., Kruk N.N., Vystavnoi S.A., Borisov S.M. et al., 2001. Major Epochs of Intrusive Magmatism of Kuznetsk Alatau, Altai, and Kalba (From U-Pb Isotope Dates). Russian Geology and Geophysics 42 (8), 1089–1109.

34. Vrublevskii V.V., Kotel’nikov A.D., Izokh A.E., 2018. The Age and Petrologic and Geochemical Conditions of Formation of the Kogtakh Gabbro-Monzonite Complex in the Kuznetsk Alatau. Russian Geology and Geophysics 59 (7), 718–744. https://doi.org/10.1016/j.rgg.2018.07.002.

35. Yakubchuk A., Degtyarev K., Maslennikov V., Wurst A., Stekhin A., Lobanov K., 2012. Tectonomagmatic Settings, Architecture, and Metallogeny of the Central Asian Copper Province. In: J.W. Hedenquist, M. Harris, F. Camus (Eds), Geology and Genesis of Major Copper Deposits and Districts of the World: A Tribute to Richard H. Sillitoe. SEG Special Publications. Vol. 16. Cenveo, Lancaster, p. 403–432.