Early–Middle Jurassic magmatism and skarn–porphyry mineralization in NE China: Geochronological and geochemical constraints from the Sankuanggou skarn Fe–Cu–(Mo) deposit, and tectonic implications

Abstract

The Early–Middle Jurassic tectonic setting of NE China is poorly defined. Mineralization of this period, especially skarn–porphyry mineralization and the ore-related magmatism, can provide well constraints on the geodynamic setting. An analysis of the spatio-temporal distribution of skarn–porphyry deposits in NE China, with the Sankuanggou skarn Fe–Cu–(Mo) deposit chosen as a typical example, was conducted in an attempt to elucidate the tectonic setting of the region. The Sankuanggou deposit is located in the Great Xing'an Range, in the eastern segment of the Central Asian Orogenic Belt. Re-Os isochron dating of molybdenites indicates the ages of the skarn- and veinlets–disseminated-type mineralization are 172.9 ± 3.3 and 173.4 ± 6.3 Ma, respectively. This suggests that the mineralization was contemporaneous with emplacement of granodiorite (175.9 ± 1.6 Ma), and related to Early Jurassic magmatism. Zircons from the Sankuanggou granodiorite have εHf(t) values of +8.7 to +11.2. Sulfur isotopic compositions (δ34S) of the sulfides range from −3.59‰ to +0.92‰, indicating that the ore-forming materials were mainly derived from magma. The Re content of molybdenite (11.3–63.3 ppm) suggests that the ore-forming materials mainly originated from a mixed crust–mantle source. Geochemical characteristics and Sr–Nd–Pb–Hf isotopic compositions suggest that the ore-forming granodiorite was formed in a continental arc setting, melts of which largely originated from partial melting of a mantle wedge induced by the subducted slab. Based on the spatio-temporal distribution of the skarn–porphyry deposits in NE China, we propose that the Early–Middle Jurassic period (200–160 Ma) is likely to have been one of the most important metallogenic epochs in NE China. These deposits formed in a continental arc setting, which was closely related to the westward subduction of the paleo-Pacific Plate during this period.