Late Cretaceous granitic magmatism and mineralization in the Yingwuling W–Sn deposit, South China: Constraints from zircon and cassiterite U–Pb geochronology and whole-rock geochemistry

Abstract

Numerous Late Cretaceous W–Sn deposits associated with granitic rocks were developed in the southern part of South China. However, the relationship among granitic magma, mineralization and tectonic setting remains disputed. The Yingwuling W–Sn deposit is spatially associated with K-feldspar granite and biotite granite in the southwestern part of Guangdong province, South China. LA-ICP-MS zircon U–Pb dating of K-feldspar granite, biotite granite and weathered ore-bearing granites yielded ages of ∼79 Ma, which agree well with the LA-ICP-MS cassiterite U–Pb age of 79.6 ± 0.9 Ma, indicating a close genetic link between the Yingwuling pluton and W–Sn mineralization. Geochemically, both K-feldspar granite and biotite granite show high SiO2, Na2O + K2O and low CaO, P2O5 contents, and they belong to shoshonitic series and high-K calc-alkaline series, respectively. High Rb/Sr ratios and low Nb/Ta and Zr/Hf ratios of the Yingwuling pluton indicate strong magmatic differentiation. Compared with K-feldspar granite, biotite granite experienced a higher degree of fractional crystallization as indicated by lower Fe2O3, TiO2, LREE, Sr, Eu, Ba and Zr contents and higher SiO2, HREE, Rb, Cs and Y contents. Their Sr and Nd isotope compositions (initial 87Sr/86Sr = 0.7027 and 0.7097; εNd(t) = −5.6 and −5.7) are less radiogenic than that of the South China basement. Thus, it is likely that some juvenile materials were involved in the formation of these granitic intrusions. This is also favored by the wide range of zircon Hf isotope values (εHf(t) = −6.6 to 0.8), which indicates mixing processes. A-type granite affinity of the Yingwuling pluton shows that it was possibly formed in an extensional setting. Late Cretaceous W–Sn deposits constitute an EW-trending belt from Guangdong to Yunnan provinces, which was compatible with the northward subduction of the Neo-Tethys plate rather than the northwestward subduction of the Pacific plate during Late Cretaceous. Combined with previous studies on magmatic rocks and tectonic activities during Late Cretaceous in South China, this study suggests that the subduction of the Neo-Tethys plate was most possibly responsible for the Late Cretaceous Yingwuling granitic intrusion and associated W–Sn mineralization.