河北省涞源县龙门斑岩型钼矿床锆石U-Pb和辉钼矿Re-Os年龄及其地质意义

Zircon U-Pb and molybdenite Re-Os dating of Longmen porphyry molybdenum deposit in Laiyuan County of Hebei Province and its geological significance

龙门钼矿床是太行山北段成矿带内近些年探明的一个大型钼矿床,钼矿体主要产于花岗斑岩、闪长岩和新太古代片麻岩中,以角砾岩型矿石为主。矿区内辉钼矿化主要类型为浸染状、薄膜状、细脉状,发育钾长石化、硅化、绢云母化、黄铁矿化蚀变,类似典型的斑岩型矿床的矿化和蚀变特征。文章对龙门钼矿床的闪长岩和花岗斑岩进行了LA-ICP-MS锆石U-Pb同位素测年,获得闪长岩的锆石谐和年龄为(138.1±0.6)Ma(MSWD=0.6,n=21),花岗斑岩的锆石谐和年龄为(137.0±0.7)Ma(MSWD=1.03,n=17),结合地质特征,显示花岗斑岩晚于闪长岩形成。对主要矿石类型中的辉钼矿进行了Re-Os同位素测年,获得辉钼矿的Re-Os等时线年龄为(136.5±1.5)Ma,与赋矿的花岗斑岩的侵位年龄相一致,二者应为同一岩浆-流体活动的产物。龙门钼矿床辉钼矿样品的w(Re)为13.1×10^(-6)~59.3×10^(-6),表明其成矿物质来源于壳幔混源。龙门矿区及太行山北段成矿带内的隐爆角砾岩体是下一步找矿勘查的方向。

The Longmen deposit is a large-sized molybdenum deposit discovered in recent years in the North Taihang Mountain metallogenic belt.The molybdenum orebodies are mainly hosted in the Mesozoic granitic porphyry,diorite and Neoarchean gneiss,and molybdenum ore is mainly of breccia type.The main ore-forming types in the deposit include dissemination,lamination,and veinlet molybdenite mineralization,and the major alteration types comprise potassic alteration,silicification,sericitization and pyritization,which are similar to typical ore-forming and alteration characteristics of the porphyry molybdenum deposit.In this paper,the authors present LA-ICP-MS U-Pb zircon age data for the diorite and granite porphyry in the Longmen molybdenum deposit.The U-Pb age of the zircon from the diorite is(138.1±0.6)Ma(MSWD=0.61,n=21)and that from the granite porphyry is(137.0±0.7)Ma(MSWD=1.03,n=17).Combined with geological characteristics,the authors hold that the granite porphyry was formed later than the diorite.The Re-Os dating of molybdenite yielded an isochron age of(136.5±1.5)Ma,which is consistent with the emplacement age of the granite porphyry.The authors thus believe that they are products of the same magma-fluid activity.The Re values of molybdenum vary in the range of 13.1×10^(-6)~59.3×10^(-6),showing that they were derived from mixed crust and mantle sources.The cryptoexplosion breccia in the Longmen area and the North Taihang Mountain metallogenic belt is the target of prospecting and exploration in the next step.