吉林延边地区浅成热液金(铜)矿床的~(40)Ar/~(39)Ar激光探针测年与成矿时代讨论

延边地区是中国东北部陆缘浅成热液金铜矿床发育的地区之一,广泛发育着浅成热液金矿床、中温热液金(铜)矿床和中深成中高温热液富金铜矿床(类斑岩型);富金铜矿床的成矿时代发生在105～102 Ma,为了进一步确定浅成热液金矿床与中深成中高温热液富金铜矿床的成矿动力学背景,采用流体包裹体的~(40)Ar/~(39)Ar激光探针定年法,对该区典型浅成热液金矿床进行了精细的年代学测定,获得刺猬沟金矿床、五星山金矿床和杜荒岭金矿床的脉石矿物石英流体包裹体的~(40)Ar/~(39)Ar等时线年龄分别为(141±7)Ma、(123±7)Ma和(107±6)Ma,其中刺猬沟金矿床((141±7)Ma)和五星山金矿床((123±7)Ma)的脉石矿物石英流体包裹体含有过剩放射性成因~(40)Ar,而杜荒岭金矿床((107±6)Ma)的脉石矿物石英流体包裹体几乎不含或含极少量过剩放射性成因~(40)Ar。结合最新获得的相关地质体的精细年代学成果,认定该区浅成热液金矿床成矿作用均发生在早白垩世晚期,或发生在早白垩世晚期火山喷发、浅成岩浆就位之后,其形成环境与富金铜矿床一致,为古太平洋板块向亚洲大陆正北向俯冲转入Izanagi-Farallon板块西向俯冲的构造转换期。

~(40)Ar/~(39)Ar laser probe dating and discussion on metallogenic epoch of epithermal Au-Cu deposit in Yanbian area of Jilin

The Yanbian area of Northeastern China developed continental margin epithermal Au-Cu deposits, where the epithermal low temperature Au deposit, the medium temperature hydrothermal Au(Cu)deposit and the medium-high temperature hydrothermal Cu deposit with Au-enrichment (like porphyry) widely occurred. The epoch of Cu deposit with Au-enrichment is 105 - 102 Ma. In order to determine the metallogenic geodynamic setting, the authors studied the chronology of the typical epithermal Au deposit using ~(40)Ar/~(39)Ar laser probe dating, and the result shows that the ~(40)Ar/~(39)Ar isochron age of gangue mineral quartz fluid inclusions in Ciweigou, Wuxingshan and Duhuangling Au deposits are (141±7) Ma, (123±7) Ma and (107±6) Ma, respectively. The gangue mineral quartz fluid inclusions of Ciweigou and Wuxingshan Au deposits contain excess radiogenic ~(40)Ar, but those of Duhuangling Au deposit contain almost none or very small amount of excess radiogenic ~(40)Ar. Combining the new acquired precise chronological results of related geologic body, the authors consider that the mineralization time of the epithermal Au deposit was the late period of the Early Cretaceous, or occurred after volcano eruption and hypabyssal magma emplacement in the late period of the Early Cretaceous, and the formation environment of the epithermal Au deposit was consistent with the Cu deposit with Au-enrichment, which was the tectonic transition period in which the north-trend subduction of the Paleo-Pacific Plate towards the Asian continent changed to the western-trend subduction of the Izanagi-Farallon Plate.