关键词: 锆石U-Pb定年, 地球化学, 岩石成因, 浅成低温热液型金矿, 小兴安岭地区

Abstract:  Yidong Linchang gold polymetallic deposit is a recently discovered gold deposit in Lesser Xing’an range. The volcanic-subvolcanic rocks are widely distributed in the mining area, among which the diorite porphyrite and dacite are closely related to the mineralization. In this contribution, we reported petrogeochemistry，zircon U-Pb ages and Sr, Nd and Hf isotope compositions of the diorite porphyrite and dacite at Yidong Linchang gold polymetallic deposit. Geochemical studies show that the volcanic-subvolcanic rocks closely related to mineralization are peraluminous calc-alkaline volcanic rocks. All these rocks have arc magma characteristics related to subduction and are enriched in LREEs and weak negative Eu anomaly, enriched in large-ion lithophile elements (Rb, Ba) and incompatible elements (Th, U), and relatively depleted of high field-strength elements (Nb, P and Ti). Zircon U-Pb ages of diorite porphyrite and dacite are (99.60±0.62) Ma and (98.50±0.50) Ma, respectively, both formed in the Early Cretaceous. Sr-Nd-Hf isotope analysis showed that the samples have high (87Sr/86Sr)i ratios (0.707 20-0.707 70), low εNd(t) values (-3.47--2.42) and εHf(t) values (-2.22-4.11), revealing that the source area is mainly mantle with the strong contamination of crustal materials. Research results reveal that the diorite porphyrite and dacite in Yidong Linchang gold polymetallic deposit were formed in the continental arc environment of the active continental margin. The magmas were likely derived from deep-formed magmas by the partial melting of the overlying mantle wedge by the fluids released by the dehydration of the subducting Pacific Oceanic plate, and are strongly contaminated by the crust during the evolution process. On the basis of the above research and combined with the regional geological background, it is inferred that the volcanic-subvolcanic rocks of the Early Cretaceous were formed in the tectonic background of lithospheric extension as a consequence of the rollback of the subducted Paleo-Pacific Oceanic plate.

Key words: zircon U-Pb dating, geochemistry, petrogenesis, epithermal gold deposit, Lesser Xing'an range