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Russian Geology and Geophysics

2003 year, number 11


V.I. Sotnikov, V.A. Ponomarchuk, D.O. Shevchenko, and A.N. Berzina
United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Porphyry Cu-Mo deposits, 40Ar/39Ar dating, 87Sr/86Sr value, S isotopes, halogens, Aksug deposit, Tuva
Pages: 1080-1092


Magmatic and ore-metasomatic processes in the Aksug Cu-Mo ore cluster were dated by the 40Ar/39Ar age method. It has been established that the formation of the Aksug porphyry Cu-Mo deposit was related to the origin of an ore-bearing porphyry complex and followed a long multistage granitoid magmatism (532-522; 497 1; 490-488; and 462 Ma). Dating of differently metasomatized ore-bearing porphyries (sericite and sericitized plagioclase) revealed three periods of endogenous events (404-401; 364-354; and 331-324 Ma) obviously corresponding to the periods of various ore-metasomatic processes: formation of stockwork pyrite-molybdenite-chalcopyrite mineralization and mineral association with native copper and chalcocite. The final stage was related to the formation of aplite-granite association (336-324 Ma), in which minor veinlet and nest pyrite-chalcopyrite mineralization was found. Despite the long overall period of endogenous processes, the 87Sr/86Sr values of accessory apatite in all studied Aksug rocks vary over a narrow range, 0.70427-0.70496, close to those in the mantle, which suggests that the parental magmas were generated at the same depths. This is consistent with the high activity of Cl, specific for all heterochronous magmatic processes, which might have been related to the dehydration of submerging oceanic plate. The expansive metasomatic transformation of country rocks at the deposit was accompanied by release of much Cl, which might seriously affect the overall balance of halogens in the ore-magmatic system. The 34S values of sulfides (0.6-3.1<194>) from ore zones are close to those of meteorites.