Lead isotope systematics of porphyry–epithermal spectrum of the Birgilda–Tomino ore cluster in the South Urals, Russia

Abstract

The paper provides the first data on lead isotopic composition of porphyry and epithermal mineralization of the Birgilda-Tomino ore cluster. Lead isotope characteristics were obtained for 24 sulfide samples representing epithermal Au-Ag (Bereznyakovskoe ore field and Michurino occurrence), base-metal carbonate replacement (Biksizak occurrence), porphyry copper (Tomino, Kalinovskoe, and Birgilda deposits), and four plagioclase samples of the Birgilda-Tomino Igneous Complex. Ore samples have lead isotopic signatures similar to neighboring intrusions of the Birgilda-Tomino igneous complex and this confirms genetic relations between epithermal Au-Ag, base-metal carbonate replacement and porphyry copper mineralization with diorite porphyry intrusions. Variations in lead isotopic composition are caused by mixing of mantle and crustal lead sources. The input of radiogenic 206Pb took place during the post-ore phase as a result of a series of tectono-magmatic events, which include emplacement of at least two phases of the Chelyabinsk pluton. The latter however could act only as a trigger of hydrothermal activity but not as a lead source.