Isotopy of lead from the Sora porphyry Cu-Mo magmatic center ( Kuznetsk Alatau)

Abstract

We studied the isotopic composition of lead in feldspars from the intrusive rocks of enclosing, ore-bearing porphyry, and post-ore complexes and in sulfides from the Sora magmatic center including the Sora porphyry Cu-Mo deposit. The arrangement of the isotopic composition points below the orogen evolution curve on the uranogenic lead diagram evidences a predominance of lead of mantle genesis in the igneous rocks and a minor content of crustal lead. On the 207Pb/ 204Pb– 206Pb/ 204Pb diagram, the lead of magmatites form a linear sequence (trend), which is interpreted as mixing of lead from different sources. According to the geochemical parameters, weakly depleted mantle metasomatized by subduction fluids was a source of magmatism. The linear correlation between the ratios of Pb isotopes in the igneous rocks of the Sora magmatic center is explained by the mixing of lead of the mantle and subduction fluids. Mantle lead is predominant in the basites of the enclosing, porphyry, and post-ore complexes and in the leucogranites of the enclosing complex. According to lead isotopy data, the differentiated magmatites (enclosing monzonitoids, ore-bearing porphyry, and post-ore syenite-porphyry) contain a subduction component, whose content increases in passing from early to late complex. The Pb-isotopic composition of sulfides suggests the mantle source of Pb in molybdenite of the breccia ores and the heterogeneous source (mantle and subduction fluids) of Pb in chalcopyrite of the veinlet ores.