冀东下营坊金矿成矿年代学研究

冀东下营坊金矿地处华北地台北缘燕山造山带东段,是该区一个重要的岩浆期后热液型金矿。该金矿产于大铜山杂岩体及外接触带中,有三种矿化类型,即斑岩型、角砾岩型、矽卡岩型,构成了典型的斑岩型金矿成矿系统。为精确厘定下营坊金矿的成矿年代,更好的理解该矿与区内其他金矿的关系,本文采用锆石U-Pb和辉钼矿Re-Os同位素定年,获得赋矿斑岩(花岗斑岩)的结晶年龄为163.32±0.90Ma,切穿矿体的煌斑岩脉结晶年龄为159.0±1.5Ma,由此限定成矿年龄可能在163.32Ma~159.0Ma之间;而由辉钼矿获得的Re-Os同位素模式年龄为164.2±2.3Ma。在误差范围内,Re-Os同位素模式年龄与U-Pb同位素年龄是一致的,表明下营坊金矿成矿年龄为164.2±2.3Ma,属于中侏罗世岩浆热液事件。结合前人研究结果,认为下营坊金矿以及冀东中侏罗世金矿的成岩成矿构造背景与区内该时期的岩浆事件一样,可能受古太平洋板块俯冲的影响而处于挤压的构造环境。

Geochronology of the Xiayingfang Au Deposit in Eastern Hebei Province

The Xiayingfang Au deposit, an important Au deposit in eastern Heibei Province, is located in the eastern side of the Yanshan orogenic belt, North China Ctraton. Its Au ore bodies can be classified into porphyry, breccia and skarn types, which are hosted in the Datongshan complex and its external contact zone, both of which are typical features of a porphyry gold metallogenic system. In order to unraveling the mineralization age of this deposit and its relation with other Au deposits in eastern Heibei Province, this work adopted zircon U-Pb and molybdenite Re-Os dating technology for chronology. The results show that zircon U-Pb ages of granite porphyry hosting Au ore bodies and lamprophyric vein cutting the ore bodies are 163.32±0.90 Ma and 159.0±1.5Ma, respectively. The mineralization age is determined as between 163.32Ma to 159.0Ma. Re-Os model age of molybdenite is 164.2±2.3Ma, which is consistent with the age gap defined by magmatic rocks, and suggests that mineralization age of the Xiayingfang Au deposit is 164.2±2.3Ma, belonging to Middle Jurassic. Combined with previous research results, this work suggests that the Xiayingfang Au deposit formed in a compressive environment influenced by the subduction of the paleo-Pacific plate, just like magma events and the Au deposits of middle Jurassic in eastern Hebei province.