Mixed crustal-mantle source of porphyry Cu-Mo deposits of the Urals: Pyrite trace element geochemistry and Pb - S isotope data

Developing genetic models of porphyry Cu-, Mo-, and Cu-Mo deposits requires knowledge on the source of metals for these deposits. Even though porphyry Cu deposits worldwide were relatively well-studied and the corresponding sources of metals were considered, porphyry Cu-Mo deposits of the Urals were not previously investigated. The paper presents new data on two porphyry Cu-Mo deposits of Paleozoic age: namely Late Devonian to Early Carboniferous Verkhneuralskoe in the South Urals and Late Carboniferous to Early Permian Talitsa in the Middle Urals. Pyrite trace element data indicate minor input of Ni, Tl, and Ag from host rocks of the Talitsa deposit. Talitsa and Vekhneuralskoe deposits are heterogeneous in Pb isotope composition and, on the contrary, homogeneous in S isotope composition which is typical for porphyry deposits worldwide. The both deposits show similar age-corrected Pb isotope compositions of sulfides (18.228 to 18.521 for( 206)Pb/Pb-204, 15.598 to 15.705 for( 206)Pb/Pb-204, and 38.087 to 38.474 for Pb-208/Pb-204) and of magmatic and hydrothermal K-feldspars (from 18.291 to 18.449 for( 206)Pb/Pb-204, from 15.598 to 15.608 for Pb-207/Pb-204, and from 38.023 to 38.127 for Pb-208/Pb-204); delta S-34 varies from-0.4 to +3.4 parts per thousand. The isotope data suggest that granitoid melts were the dominant source of both sulfides and ore-bearing magmatic rocks. Mantle-crustal mixing model calculated for the Urals shows 95 % of mantle Pb in porphyry Cu-Mo deposits.

Automated summary

This paper investigates the source of metals for two Paleozoic porphyry Cu-Mo deposits in the Urals, providing new data and suggesting that granitoid melts were the dominant source. The lead isotope composition of the deposits is heterogeneous, while the sulfur isotope composition is homogeneous, consistent with typical porphyry deposits worldwide. The results indicate that 95% of the mantle lead is present in the porphyry Cu-Mo deposits in the Urals.