闽中德化邱埕钼矿床辉钼矿Re-Os同位素定年及其对成矿时间的限定

Molybdenite Re-Os dating of the Qiucheng Mo deposit in Dehua of central Fujian Province and constraints on the mineralization time

福建德化邱埕钼矿床是德化—尤溪—永泰矿集区唯一一处规模较大的钼矿床。辉钼矿体分布在花岗斑岩外接触带,辉钼矿多沿中新元古代变质岩和晚侏罗世花岗岩裂隙分布,多呈浸染状、脉状和团块状。本次测得该矿床6件辉钼矿样品Re-Os模式年龄为150.1~152.8 Ma,^(187)Re-^(187)Os等时线年龄为(150.8±1.6)Ma,加权平均年龄为(151.8±0.9)Ma,表明成矿时代为晚侏罗世晚期,与该地区大规模的火山-侵入体活动相关;Re/Os比值远大于4,Re同位素含量14.31×10^(-6)~45.8×10^(-6)(最高达174.7×10^(-6)),指示成矿物质主要来源于壳源,可能还有少量幔源物质的加入。邱埕钼矿床的形成可能为古太平洋板块朝东亚陆缘碰撞挤压作用结束向伸展作用转化过程的产物。

The Qiucheng Mo deposit is located in the Dehua-Yongxi-Yongtai ore-concentrated area of Fujian Province.It is the only one large-scale molybdenum deposit there.Ore bodies are mainly distributed in the outer contact of granite porphyry,fissure filling of the middle-late Proterozoic metamorphic rocks and the late Jurassic granites.The molybdenite is disseminated,veins and lump.Re-Os dating of six molybdenite samples collected from the main ore body in the deposit yields the model age from 150.1 Ma to152.8 Ma,the isochron age of(150.8±1.6)Ma,and the weighted average age of(151.8±0.9)Ma.It can thus be considered that the deposit was formed in the late stage of Late Jurassic and related to the large-scale volcanic and intrusive rock activities.According to the rhenium content(14.31×10^(-6)-45.8×10^(-6)(one is 174.7×10^(-6)))and the ratio of Re and Os(much greater than 4)of molybdenum samples,it is inferred that the ore-forming materials of the deposit were mainly derived from the crust and possible addition of small amount of mantle materials.The Qiucheng Mo deposit may be the product of conversion process from the end of collision to the beginning of extension of the Paleo-Pacific plate towards the continental margin of East Asia.