Isotopic analysis of the super-large Shuangjianzishan Pb-Zn-Ag deposit in Inner Mongolia, China: Constraints on magmatism, metallogenesis, and tectonic setting

The super-large Shuangjianzishan Pb-Zn-Ag deposit is a newly discovered deposit located in the Huanggang-Ganzhuermiao polymetallic metallogenic belt of Inner Mongolia, NE China. The deposit's resource includes 0.026 Mt Ag, 1.1 Mt Pb, and 3.3 Mt Zn. The deposit is controlled by a NW-trending ductile shear zone and NE and NW-trending faults in black pelite assigned to the lower Permian Dashizhai Formation. LREE enrichment, HREE depletion, Nb, Ta, P, and Ti depletion, and Zr and Hf enrichment characterize felsic magmatic rocks in the Shuangjianzishan Pb-Zn-Ag district. The ages of porphyritic monzogranite, rhyolitic crystal-vitric ignimbrite, and porphyritic granodiorite are 254-252,169, and 130 Ma, respectively. Pyrite sampled from the mineralization has Re-Os isochron ages of 165 +/- 7 Ma, which suggest the mineralization is associated with the ca. 169 Ma magmatism in the Shuangjianzishan district. Zircons extracted from the porphyritic granodiorite yield epsilon(Hf)(t) values of -11.34 to -1.41, with t(DM2) dates of 1275-1901 Ma. The epsilon(Hf)(t) values of zircons in the rhyolitic crystal-vitric ignimbrite and the ore-bearing monzogranite porphyry are 7.57-16.23 and 10.18-15.96, respectively, and their t(DM2) ages are 177-733 and 257-632 Ma, respectively. Partial melting of depleted mantle resulted in the formation of the ca. 254-252 Ma ore-bearing porphyritic monzogranite and the ca. 169 Ma rhyolitic crystal-vitric ignimbrite; dehydration partial melting of subducted oceanic crust resulted in the formation of the ca. 130 Ma porphyritic granodiorite. The porphyritic monzogranite was emplaced during the late stages of closure of the Paleo-Asian Ocean during the transformation from a collisional to extensional tectonic setting. The ca. 170 and ca. 130 Ma magmatism and mineralization in the Shuangjianzishan district are related to subduction of the Mongolia-Okhotsk Ocean and subduction of the Paleo-Pacific Ocean Plate, respectively. (C) 2015 Elsevier B.V. All rights reserved.