Lead Isotope Characteristics of the Mindyak Gold Deposit, Southern Urals: Evidence for the Source of Metals

Abstract

The isotopic composition of Pb in pyrite of the Mindyak orogenic gold deposit located in the Main Ural Fault Zone, the Southern Urals, has been studied by the high-precision MC-ICP-MS method. Orebodies at the deposit are composed of early pyrite and late polysulfide–carbonate–quartz mineral assemblages. The orebodies are localized in olistostrome with carbonaceous clayey-cherty cement. Pyrites from early and late mineral assemblages are close in Pb isotope ratios. For early pyrite ²⁰⁶Pb/²⁰⁴Pb = 18.250–18.336, ²⁰⁷Pb/²⁰⁴Pb = 15.645–15.653, ²⁰⁸Pb/²⁰⁴Pb = 38.179–38.461; while for late pyrite ²⁰⁶Pb/²⁰⁴Pb = 18.102–18.378, ²⁰⁷Pb/²⁰⁴Pb = 15.635–15.646, ²⁰⁸Pb/²⁰⁴Pb = 38.149–38.320. The model parameters μ₂ (²³⁸U/²⁰⁴Pb = 9.91 ± 2), ω₂ (²³²Th/²⁰⁴Pb = 38.5 ± 4), and ²³²Th/²³⁸U = 3.88 ± 3 indicate that an upper crustal Pb source played a leading role in ore formation. Carbonaceous shale as an olistostrome cement and syngenetic sulfide mineralization are considered to be the main Pb sources of both early and late mineral assemblages. An additional recept in apparently magmatic lead is suggested for the late veinlet mineralization. The involvement of lead from several sources in ore formation is consistent with the genetic model, which assumes a two-stage formation of orebodies at the Mindyak deposit.