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

Abstract

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 206Pb/204Pb, 15.598 to 15.705 for 206Pb/204Pb, and 38.087 to 38.474 for 208Pb/204Pb) and of magmatic and hydrothermal K-feldspars (from 18.291 to 18.449 for 206Pb/204Pb, from 15.598 to 15.608 for 207Pb/204Pb, and from 38.023 to 38.127 for 208Pb/204Pb); δ34S varies from −0.4 to +3.4 ‰. 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.