Early Cretaceous Sn-bearing granite porphyries, A-type granites, and rhyolites in the Mikengshan–Qingxixiang–Yanbei area, South China: Petrogenesis and implications for ore mineralization

Abstract

A world-class Sn province in South China contains granite- and porphyry-related Sn deposits. In this paper, we investigate the source of Sn, based on a study of Early Cretaceous (145–134 Ma) ore-barren granites and granite porphyries, ore-barren rhyolites, and Sn-bearing granite porphyries in the Mikengshan (MKS)–Qingxixiang (QXX)–Yanbei (YB) area of South China. The ore-barren rhyolites have enriched whole-rock Nd and zircon Hf isotopic compositions [εNd(t) = − 9.1 to − 10.5; εHf(t) = − 5.9 to − 13.8]. The ore-barren granites and granite porphyries have A-type granite characteristics and less enriched Nd–Hf isotopic compositions [εNd(t) = − 4.9 to − 3.2; εHf(t) = − 6.0 to + 1.7] than the ore-barren rhyolites. The Sn-bearing granite porphyries have similar rare earth element and trace element patterns to the ore-barren rhyolites. In addition, they have similar Nd but less enriched Hf isotopic compositions [εNd(t) = − 8.9; εHf(t) = − 3.3 to + 0.4] compared with the ore-barren rhyolites. The average ΔFMQ values of the studied volcanic (–0.50) and intrusive (–0.21) rocks indicate reduced condition during magma evolution. We suggest that the ore-barren rhyolites were likely derived by partial melting of Paleoproterozoic to Mesoproterozoic crustal metasedimentary rocks and that the Sn-bearing granite porphyries were possibly formed by partial melting of Paleoproterozoic metasomatized mantle-derived crustal rocks. Whereas, the ore-barren granites and granite porphyries were likely generated by partial melting of a hybridized source consisting of ancient and late Mesozoic juvenile crustal rocks. We propose that the reduced redox state and ancient crustal sources played an important role for Sn mineralization in the MKS–QXX–YB area.