Magmatism and metallogeny associated with mantle upwelling: Zircon U-Pb and Lu-Hf constraints from the gold-mineralized Jinchang granite, NE China

The Jinchang gold deposit is located in the easternmost portion of the Central Asian Orogenic Belt (CAOB), and represents one of the major gold districts in eastern Jilin-Heilongjiang provinces of China. The gold ore bodies are hosted mainly in altered Mesozoic granitoids, breccia pipes and ring and radial faults. Gold mineralization consists of alteration (stockwork in hydrothermally altered granites), breccia, and quartz-sulfide vein-types. Alteration assemblages around the alteration-style ore body show a vertical sequence of potassic, phyllic, and propylitic zones. In this study, we present U-Pb and Lu-Hf isotope data on zircons derived from mineralized granophyric granite, biotite monzogranite, granodiorite, and granite porphyry, and sericite Rb-Sr ages from the Jinchang gold deposit. The results show Pb-206/U-238 ages of 201 +/- 3 Ma (MSWD = 1.1), 203 +/- 4 Ma (MSWD = 1.4), 201 +/- 5 Ma (MSWD = 2.1), and 110 +/- 3 Ma (MSWD = 1.6), respectively. Sericite from the gold-mineralized phyllic-altered granodiorite and granite porphyry returns Rb-Sr isochron ages of 110 +/- 4 Ma (MSWD = 1.04) and 107 +/- 5 Ma (MSWD = 0.91), respectively. Our new data indicate that the gold mineralization at Jinchang took place at ca. 110 Ma and was temporally related to intrusion of the granite porphyry. Zircon epsilon Hf (200 Ma) values of the ca. 200 Ma granites vary from -4.8 to + 8.1, with T-DM(C) model ages of 727-1535 Ma, reflecting their derivation mainly by partial melting of juvenile Proterozoic crust. The gold-bearing 110 Ma granite porphyry returns epsilon Hf (110 Ma) values in the range of -1.6 to + 9.8, with T-DM(C) model ages of 542-1069 Ma, suggesting partial melts of juvenile Proterozoic crust with notable input of mantle components as compared to the ca. 200 Ma granites. Compiled oxygen (delta O-18(SMOW) = 0.7-10.1) and hydrogen (delta D-SMOW = 99 to -70) stable isotopic values of quartz from ores indicate that the ore-forming fluids were predominantly exsolved from magmas with minor amount of meteoric water in quartz-sulfide veins at the late stage. The Hf isotope data from the granite porphyry, integrated with the results from previous data on S and Pb isotopic composition of ores, constrain the source of ore-forming components as lower crust with discernible mantle inputs and wall rock assimilation. Our results have implications bearing on the widespread magmatism and metallogenic event during the Early Cretaceous time in East China, and link them to mantle upwelling that contributed both heat and volatiles for crustal melting and scavenging of metals which in turn were concentrated in upper crustal levels through exsolution for the magmas. (c) 2013 Elsevier B.V. All rights reserved.