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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。
The Jidong Xiayingfang gold deposit is located in the eastern section of the Yanshan orogenic belt on the northern margin of the North China Platform, and is an important post-hydrothermal gold deposit in the area. The gold deposit is produced in the Da Tongsan complex and in the outer contact zone. There are three mineralization types, namely porphyry type, breccia type and skarn type, which constitute the typical porphyry type gold mineralization system. In order to accurately determine the metallogenic age of the Yingfang Gold Mine and to better understand its relationship with other gold deposits in the area, zircon U-Pb and Re-Os isotopic dating of molybdenite were used to obtain porphyry (Granite porphyry) is 163.32 ± 0.90Ma. The crystallization age of the lamprophyre vein cut through the ore body is 159.0 ± 1.5Ma, which limits the mineralization age to be between 163.32Ma and 159.0Ma. The molybdenite obtained Re-Os isotope pattern age of 164.2 ± 2.3Ma. Within the error range, the Re-Os isotopic pattern age is consistent with the U-Pb isotopic age, indicating that the age of the Xiayingfang Gold Mine is 164.2 ± 2.3Ma and belongs to the Middle Jurassic magmatic hydrothermal event. Combined with the results of previous studies, it is concluded that the diagenetic and mineralization tectonic settings of the Xiayingfang Gold Mine and the Jidong Middle Jurassic gold deposit are the same as the magmatic events in this period and may be affected by the subduction of the Paleo-Pacific plateau in the tectonic setting .