Late Jurassic Sn metallogeny in eastern Guangdong, SE China coast: Evidence from geochronology, geochemistry and Sr–Nd–Hf–S isotopes of the Dadaoshan Sn deposit

Abstract

The newly discovered Dadaoshan Sn deposit is located in the eastern Guangdong Sn–W province, coastal SE China. The Sn mineralization, hosted in Jurassic porphyritic granite and the Lower Jurassic Jinji Formation sedimentary wall rocks, is considered to be granite-related. In this study, the porphyritic granite was LA–ICP–MS zircon U–Pb dated to be 153.2±1.2Ma, consistent with the syn-mineralization molybdenite Re–Os age of 152.6±1.8Ma. The porphyritic granite samples are weakly peraluminous (A/CNK=1.0–1.1) and high-K calc-alkaline. The rocks contain high SiO2 (72.9–75.6wt%), moderate Rb/Sr (5–9) and low ΣREE (136–223ppm). They are enriched in F, Li, Rb and Sn, depleted in Ba, Sr, P, Zr, Th, Nb and Y, and have distinct negative Eu anomalies (δEu=0.09–0.18), suggesting that the porphyritic granite is highly fractionated I-type granite. The calculated initial 87Sr/86Sr (0.711582–0.715173), relatively low ɛNd(t) (−9.48 to −8.54; TDM2=1638–1814Ma), and the zircon εHf(t) (−14.2 to −5.1; two-stage model ages=1528–2103Ma) all suggest that the granite was mainly crustal-derived with little mantle input. Sulfur isotopic compositions for the sulfides (arsenopyrite and chalcopyrite: δ34S=−1.1 to 1.4‰, average=−0.1) imply a dominantly magmatic sulfur source. The calculated zircon Ce4+/Ce3+ and EuN/EuN∗ ratios of the Dadaoshan granite range from 1.0 to 112 (mean=31.7) and from 0.04 to 0.37 (mean=0.14), respectively, indicating a low oxygen fugacity for the magma. The reducing and highly fractionated nature of the Dadaoshan granitic magma may have played a key role in the Sn mineralization.It was previously argued that the Jurassic Sn–W mineralization and its causative magmatism were largely confined in the South China interior, e.g., the Nanling Range. Our new data suggest that the Late Jurassic Sn–W mineralization and its causative magmatism actually extended to the SE China coastal area. The Dadaoshan granite may have been generated from partial crustal melting led by underplating of mantle-derived magmas in an extensional environment. Regional extension may have been related to the west-directed, flat-slab subduction and delamination of the Paleo-Pacific (Izanagi) plate beneath the South China block. Another suite of Early Cretaceous Sn–W-bearing granitic rocks in eastern Guangdong may have mainly been crustal-derived with minor mantle input, and likely occurred under back-arc extensional setting led by the Paleo-Pacific subduction rollback.