吉林省海沟金矿脉岩锆石U-Pb年龄及其成矿意义

U-Pb Dating of Syn-Mineralization Dykes of the Haigou Gold Deposit,Jilin Province and Its Metallogenic Significance

海沟金矿成矿期正长闪长斑岩脉岩中包含捕获碎屑锆石和岩浆结晶锆石。其中:岩浆结晶锆石U-Pb年龄的加权平均值为(132.4±1.5)Ma(n=18,MSWD=0.48,概率为0.96),可代表脉岩结晶年龄;在锆石U-Pb谐和年龄图上样品的上交点年龄为(2 460±29)Ma,下交点年龄为(137±18)Ma,前者可代表捕获碎屑锆石的成岩年龄,后者与脉岩中岩浆结晶锆石测年结果相近。综合分析认为,海沟金矿的成矿年龄应为132.4～128Ma,是陆内碰撞造山向伸展造山的构造转换时期。软流圈地幔隆起及其有关的地质和成矿作用是海沟金矿形成的主因。大海沟辉长闪长岩体为成矿同期同源岩体,其成岩年龄应代表海沟金矿成矿年龄的上限。

Two types of zircon,magmatic crystalline and captured fragment,are recognized in a syn-mineralization dyke（kjelsasite porphyry） sample collected from the Haigou gold deposit and used for zircon U-Pb dating.The averaged U-Pb age of the magmatic crystalline zircons of the sample is（132.4±1.5） Ma（n=18,MSWD=0.48,Probability=0.96）,indicating the formation age of the dyke.The upper and lower intersection ages of the zircons at U-Pb concordant plot are（2 460±29） Ma and（137±18） Ma respectively,probably representing the ages of the captured zircon fragments and forming age of the dyke.Comprehensive study indicates that gold mineralization in the Haigou gold deposit took place at about 132.4-128 Ma,a transitional period between the orogenic collision and post-orogenic extension.It is suggested that the asthenospheric upwelling and related geological and mineralization processes are the main cause for the formation of the Haigou gold deposit.The Dahaigou pyroxene diorite stock at the southeastern corner of the mine is thought to be coeval and cogenetic with the syn-mineralization dykes in the mine and its age gives the upper limit of the ore forming age.