内蒙古中东部油房西Pb-Zn-Ag多金属矿床辉钼矿Re-Os同位素年龄及地质意义

Re-Os isotopic dating of molybdenite separates from Youfangxi Pb-Zn-Ag polymetallic deposit, Inner Mongolia

油房西Pb-Zn-Ag多金属矿床为近年来在兴蒙造山带内发现的中型脉状矿床,伴生Cu和Mo。该矿床主要产出于潜火山机构外侧的断裂系统内,与潜火山活动有明显的空间关系。成矿作用可以划分为3个阶段,即:早期钼矿化阶段;主成矿期铅、锌和银矿化阶段,伴生铜;晚期碳酸盐化阶段。早期钼矿化阶段,细脉浸染状钼矿化主要产出于潜火山相的花岗斑岩内,矿化较弱,伴随轻微的钾化和强烈的硅化和黄铁矿化,后期叠加了强烈的泥化;主成矿阶段,主要形成脉状闪锌矿、方铅矿、黄铁矿以及次要的黄铜矿化,以脉状充填产出于围岩裂隙内,围岩蚀变主要为硅化,局部有强烈的萤石化;晚期碳酸盐化阶段,主要发生绿泥石化和碳酸盐化。为进一步查明油房西矿化区成矿作用发生的时间,文章对矿床早期钼矿化阶段形成的辉钼矿开展了Re-Os同位素分析,4件样品分析结果获得的模式年龄加权平均值为(138.4±1.2)Ma,MSWD值为0.63,等时线年龄为(136.4±4.9)Ma。结果表明油房西地区Pb-Zn-Ag多金属矿床形成时间为早白垩世,属燕山期构造-岩浆活动的产物。

Located in the eastern segment of the CAOB, the Youfangxi deposit in the mid-east Inner Mongolia is a newly found medium-sized Pb-Zn-Ag polymetallic deposit. The orebodies mainly occur in the fracture system outside the subvolcanic edifice, and are closely related to the subvolcanic activity. The mineralization process can be divided into three stages： the early stage of molybdenum mineralization; the main mineralization stage of the lead, zinc and silver;and the late carbonate stage. The weak mineralization of veinlet-disseminated molybdenites at the early stage is mainly located within granite porphyry of subvolcanic facies and is associated with weak potassium alteration and strong silicification and pyritization. The main metallogenic stage is composed of veinlike chalcopyrite, sphalerite, galena and pyrite,and the alteration of the wall rock is mainly silicification with minor intense fluoritization. The late stage consists of chloritization and carbonatization. Four molybdenite separates from the main orebody yielded a Re-Os weighted mean model age of（ 138. 4 ± 1. 2） Ma and an isochron age of（ 136. 4 ± 4. 9） Ma. These data indicate that the mineralization at the Youfangxi Pb-Zn-Ag deposit was associated with the Early Cretaceous intraplate granitoid magmatism.