Highly fractionated Early Cretaceous I-type granites and related Sn polymetallic mineralization in the Jinkeng deposit, eastern Guangdong, SE China: Constraints from geochronology, geochemistry, and Hf isotopes

Abstract

The recently discovered Jinkeng deposit, located in eastern Guangdong Province, SE China, is a granite-related cassiterite–sulfide-type Sn–Cu–Pb–Zn deposit in the Cathaysia Block. Zircon U–Pb dating of the biotite granite and fine-grained granite associated with the deposit yielded concordant ages of 144.7±0.8Ma and 141.1±1.3Ma, respectively. These ages are consistent, within error, with the molybdenite Re–Os isochron age of 139.3±2.5Ma for the deposit, indicating a temporal link between the emplacement of granitic plutons and polymetallic Sn mineralization. Combined with the regional mineralization ages, we propose that the 145–135Ma interval represents another significant period of Sn–W mineralization in southern China, in addition to those already recognized. The biotite granite and fine-grained granite have similar geochemical characteristics; both are weakly peraluminous, high-K and calc-alkaline, containing abundant Si, Na, and K, and low concentrations of Fe, Mg, Ca, and P. Compared to primitive mantle and unfractionated granitoids, they are enriched in Rb, Th, U, K, and Pb, have relatively high Rb/Sr and low K/Rb values, are depleted in Ba, Sr, and Ti, and have prominent negative Eu anomalies (δEu=0.05–0.19), characteristic of highly fractionated I-type granites. Zircons from these granites have εHf (t) values ranging from −9.2 to −3.3, and Hf model ages (TDM2) of 1776–1406Ma, suggesting that the granites formed by the partial melting of Proterozoic basement material, and contain a minor mantle-derived component. Highly fractionated and reduced (fO2 below NNO) magma facilitated the enrichment of Sn. Existing knowledge on the tectonic evolution of this region and new data from this study, indicate that the granites and associated Sn mineralization in the Jinkeng deposit formed in an extensional environment at ~140Ma, likely related to the rollback of the paleo-Pacific Plate.