南泥湖—三道庄钼(钨)矿的成岩成矿年龄新数据及其地质意义

南泥湖—三道庄矿床是东秦岭地区最大的斑岩-矽卡岩型钼（钨）矿,研究采用LA-ICP-MS方法对南泥湖—三道庄矿区内南泥湖花岗岩体和花岗斑岩脉开展锆石U-Pb法测年,获得矿区内花岗岩成岩年龄为（145.2±1.5）^146.7±1.2Ma。采集南泥湖矿区网脉状辉钼矿化样品和三道庄矿区浸染状辉钼矿化样品开展ICP-MS法辉钼矿Re-Os同位素测年,获得10个样品的模式年龄为（143.4±2.0）^146.5±2.3Ma（加权平均年龄为145.03±0.69 Ma）,等时线年龄为（146.0±1.1）Ma。表明矿区内花岗岩与矿脉的形成年龄一致,具有密切的成因联系。另外,此次测年工作确认了前人曾提出的158 Ma左右岩浆-热事件的存在,还揭示出东秦岭地区在175 Ma左右曾经历过另外一次岩浆热事件。前人测得南泥湖岩体年龄与其真实的形成年龄相差较大,这是因为岩浆岩中的锆石来源不均一,而测试的锆石数量有限,采用测量数据的加权平均值不能真实地代表岩浆岩中全体锆石的年龄特征。

New geochronological data of granites and ores from the Nannihu-Sandaozhuang Mo(W) deposit

The Nannihu-Sandaozhuang molybdenum deposit is the largest porphyry-skarn type deposit in eastern Qinling region.This paper reports new LA-ICP-MS zircon U-Pb age data of granitoids(including granitic veins) and ICP-MS molybdenite Re-Os isotopic age data of the samples from the mining area.The obtained formation ages of granitoids are 145.2±1.5 ~ 146.7±1.2Ma,and the model ages of 5 molybdenite samples from stockwork in the Nannihu mining area and 5 molybdenite samples from disseminated skarn in the Sandaozhuang mining area are 143.4±2.0 ~ 146.5±2.3Ma with isochron age of 146.0±1.1Ma.These new geochronological data show explicitly that the granitoids and ores were formed simultaneously,suggesting their genetic relationship.Furthermore,these new data have confirmed the existence of magma-thermal event at about 158Ma revealed by previous dating work,and also for the first time revealed that the eastern Qinling area once underwent another magma-thermal event at about 175Ma.The published weighted average age data are of distinct deviation from the real intrusive age of the Nannihu magmatic body,which results from 1) nonhomogeneous origin of zircons in magmatic rock and 2) unrepresentative dating of zircon group.