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

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 +/- 1.2 Ma, consistent with the syn-mineralization molybdenite Re-Os age of 152.6 +/- 1.8 Ma. The porphyritic granite samples are weakly peraluminous (A/CNK =1.0-1.1) and high-K talc-alkaline. The rocks contain high SiO2 (72.9-75.6 wt%), moderate Rb/Sr (5-9) and low EREE(136-223 ppm). 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 (delta Eu = 0.09-0.18), suggesting that the porphyritic granite is highly fractionated I-type granite. The calculated initial Sr-87/Sr-86 (0.711582-0.715173), relatively low epsilon(Nd)(t) (-9.48 to -8.54; T-DM2 =1638-1814 Ma), and the zircon epsilon(Hf)(t) (-14.2 to -5.1; two stage model ages = 1528-2103 Ma) all suggest that the granite was mainly crustal-derived with little mantle input. Sulfur isotopic compositions for the sulfides (arsenopyrite and chalcopyrite: delta S-34 = -1.1 to 1.4%,, average = -0.1) imply a dominantly magmatic sulfur source. The calculated zircon Ce4+/Ce3+ and Eu-N/Eu-N(*) 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. (C) 2016 Elsevier B.V. All rights reserved.