Early Jurassic magmatism and metallogeny in the Yizuomao area, Lesser Xing'an Range-Zhangguangcai Range, NE China: Evidence from petrogeochemistry, zircon U-Pb ages, and Hf isotopes

The Yizuomao area, located in the south segment of Lesser Xing'an Range-Zhangguangcai Range, is an important part of ore-concentrated area in the east of Ha'erbin. The Yizuomao Complex comprises medium- to coarse grained, medium- to fine-grained and fine-grained biotite-bearing alkali feldspar granite, and the results show( 206)Pb/U-238 ages of 195.3 +/- 1.8 Ma, 200.6 +/- 3.2 Ma and 205.2 +/- 4.1 Ma, respectively. The geological char- acteristics for these deposits indicate that a genetic link between the emplacement of granite porphyries and skarn-type mineralization. The ages of regional mineralization and crystallization of the granite porphyrie suggest that skarn mineralization in the Yizuomao area occurred during the late Early-early Middle Jurassic. The Yizuomao Complex and associated granite porphyries have similar characteristics, as both comprise high-K calc-alkaline rocks containing high concentrations of SiO2 and K2O + Na2O, and low concentrations of Ti, Fe, Mn and Ca. The magmatic rocks are depleted in Ba, Nb, Sr, and Ti, and enriched in Rb, Th, U, K and Pb, and have high Rb/Sr ratios, characteristic of highly fractionated I-type granites. Moreover, all display positive epsilon(Hf)(t) values from + 5.6 to + 14.3, and young zircon Hf single-stage and two-stage model ages, suggesting a significant contribution of juvenile material. Based on the geochronology, geochemistry and Hf isotopic data, we suggest that the Yizuomao Complex and associated granite porphyries were derived from partial melting of juvenile crust. The Yizuomao Complex was emplaced in the transformation period from the post-collision extension of the NCC and the Jiamusi-Khanka Massif to the subduction of Paleo-Pacific Plate. The granite porphyries that are intimately associated with the mineralization were the result of magmatic activity along an active continental margin related to subduction of the Paleo-Pacific Plate.