Литосфера (Oct 2017)
Systematization of u-pb zircon ages of granitoids from the copper porphyry deposits on the urals
Abstract
There is a generalization of U-Pb age of zircons from the copper-porphyry deposits of the eastern slope of the Urals. Approved reserves of the largest ones are about 1.4-1.8 Mt of Cu (at an average content of 0.4-0.6 wt % of Cu). Porphyry mineralization is confined to the small massifs of quartz-diorite composition, localized exclusively within sub-meridional volcanic areas of island-type separated by sialic zones. U-Pb ages were determined by LA ICP-MS, Goethe University Frankfurt (Germany), by SHRIMP-II, VSEGEI (St.Petersburg, Russia) and by SHRIMP-IIe/mc, IBERSIMS, Granada University (Spain). In the South Urals lateral section from east to west (approximately 160 km) the age of some quartz diorite porphyry deposits decreased from D1-2 (390 and 380 Ma, the Gumeshky and small Voznesensk deposits in Tagilo-Magnitogorsk Megazone) to D2-C11 (362 and 356 Ma, major Mikheyevsk deposit Tarutinsk deposit in the eastern part of the East-Ural volcanic megazone) and C12 (336 and 335 Ma, Benkalinsk, Zhaltyrkol’sk deposits in Valeryanovka zone). In addition, in the western part of the East-Ural volcanic megazone (in Uvelka allochthonous tectonic structure) there are S1-2 ore-bearing porphyry quartz-diorite massifs. They include the large industrial Tomino-Bereznyaki ore cluster with epithermal and porphyry mineralization (427-429 Ma) and of Zelenodolsk porphyric deposit (418 Ma) located at the distance of 25 km to the South. In indicated direction, ore specificity also changеs: Cu-(Au)- and Au-Cu-porphyric deposits are replaced by Cu-(Au, Mo)-porphyric ones. Within the Magnitogorsk zone from the early- to the late island-arc stage, the age of ore-bearing granitoids decreases (390, 381, 374 and 362 Ma), at that time their composition changes from diorite to shoshonite. Isotopic and petrogeochemical data suggest that considered island-type diorite is perhaps the result of selective melting of metabasalts of low crust or of depleted mantle (mantle wedge). This melting occurred repeatedly according to the displacement in time of its source from the west to the east of the Urals.
