Geochemical characteristics and lead isotope systematics of highly fractionated Li–F-enriched amazonite granites and related host rocks of the Orlovka–Spokoinoe mining district, Eastern Transbaikalia (Russia)

Abstract

Element concentrations and Pb isotope data are reported for the Khangilay, Orlovka and Spokoinoe granite massifs and their host rocks in the Orlovka–Spokoinoe mining district, Eastern Transbaikalia, Russia. The aim of the paper is to characterise the evolution trends and geochemical features of the Khangilay pluton and the Orlovka and Spokoinoe deposits and to study the genesis of the three granite massifs by examining fluid–rock and crust–mantle interaction in the evolution of granitoid magmatism. Zr/Hf, Y/Ho and Rb/Sr demonstrate that all three granite bodies show a continuous fractionation history from parental biotite–muscovite granites of Khangilay to highly evolved ore-bearing amazonite granites of Orlovka. Khangilay and its derivates Spokoinoe and Orlovka represent different evolution stages. REE patterns of the amazonite granites of Orlovka show a stronger Eu anomaly and more apparent REE tetrad effects in comparison with the less evolved granites of Khangilay. Pb isotope analyses indicate one common Pb source for all three granite massifs reflecting a homogenous source melt from which all magmatic members generated. Based on Pb isotope systematics two possible scenarios for the source of Li–F granites are proposed: (i) a crust–mantle source where a mixture of MORB and continental-derived material were brought together in the orogenic environment; and (ii) type II enriched mantle source where subducted continental material could have been strongly implicated in volcanic suites.