Origin of the Wunugetushan porphyry Cu–Mo deposit, Inner Mongolia, NE China: Constraints from geology, geochronology, geochemistry, and isotopic compositions

Abstract

The Wunugetushan porphyry Cu–Mo deposit is located in the southeastern margin of the Mongol–Okhotsk Orogenic Belt and in the northwestern segment of the Great Xing’an Range, NE China. The orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith. The SHRIMP zircon U–Pb dating of the granitic porphyry dyke yielded ages of 201.4±3.1Ma (2σ, MSWD=1.5). These results indicate that the magmatism in the Wunugetushan area might have occurred at ca. 201Ma in the early Jurassic, and that the mineralization age (ca. 181Ma) of this deposit is later than the age of intrusive granitic porphyry in the area. Geochemically, the Wunugetushan granitoids belong to high-K calc-alkaline and shoshonitic series, enriched in K, Rb, Nd, and Pb, and depleted in Sr, Nb, Ti and P, with negative Eu anomalies. In situ Hf isotopic analyses of zircons using LA-MC-ICP-MS indicate that the εHf(t) values for zircons from a granitic porphyry sample vary from +2.4 to +11.8 and that the corresponding crustal model ages (TDMC) vary from 483 to 1088Ma. The least-altered monzogranitic porphyry, granitic porphyry and biotite granite yielded relatively uniform εNd(t) values from −1.0 to +0.6 and low (87Sr/86Sr)i ratios ranging from 0.704387 to 0.708385. The geochemical and Sr–Nd–Hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust. The δ34S values of sulfides show a narrow range (+0.76‰ to +3.20‰) similar to those of magmatic sulfur, further implying a lower crust origin. Based on the results of this study and the regional geodynamic evolution, it is proposed that the formation of the Wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Massif during the early Jurassic, and that the monzogranitic porphyry intrusions in Wunugetushan area probably provided important ore metals responsible for the large-scale Cu–Mo mineralization.