豫西小秦岭地区大湖金(钼)矿床Re–Os和Ar–Ar同位素定年:对成矿期次的限定

Re–Os and Ar–Ar dating of the Dahu Au(Mo)deposit in the Xiaoqinling area,West Henan:Constraint on its metallogenetic stages

【研究目的】位于华北克拉通南缘的东秦岭钼矿带是全球第二大钼矿带,其北缘蕴含有著名的小秦岭造山型金矿田。近年来通过地质调查工程的实施,在小秦岭大湖金(钼)矿区深部发现具有工业意义的钼矿化,并已开始开采钼矿,限定其成矿期次,有助于研究金钼成矿规律。【研究方法】本文基于小秦岭地区危机矿山深部找矿工作,研究了金钼深部成矿模式,分析了辉钼矿Re–Os和钾长石^(40)Ar/^(39)Ar同位素定年在划分成矿期次中的作用。【研究结果】来自S35矿脉的6件辉钼矿样品Re–Os模式年龄介于(192.3±2.9)~(223.4±3.2)Ma,等时线年龄为(214.9±5.2)Ma(MSWD=0.77),来自F5矿脉中钾长石晶体^(40)Ar/^(39)Ar坪年龄为(95.22±1.16)Ma,其等时线年龄为(95.10±4.57)Ma。【结论】辉钼矿年龄代表了印支期钼矿化事件,钾长石年龄反映存在燕山中期新的构造-岩浆-热事件,这期热事件对于金钼矿床的成矿活动可能有积极意义,叠加改造了印支期的钼矿化事件。结合手标本和BSE图像分析结果,认为大湖金(钼)矿区与金钼矿化相关的热事件应不低于两期。

This paper is the result of mineral exploration engineering.Objective The East Qinling molybdenum belt which located in the North China craton is the second largest Mo belt in the world,among which occur the most famous orogenic gold deposits of the Xiaoqinling.In recent years,through the implementation of geological survey engineering,molybdenum mineralization with industrial significance has been found in the deep of Dahu Au(Mo)deposit from Xiaoqinling area,and molybdenum ore mining has begun.Through the constraint on its metallogenetic stages,it is helpful to study the Au−Mo metallogenic regularity.Methods In this paper,based on the Crisis Mine deep−seated deposits prospecting in Xiaoqinling area,we studied the metallogenic model of deep Au(Mo)deposit,and analyzed the role of molybdenite Re–Os and K–feldspar ^(40)Ar/^(39)Ar isotope dating in the classification of metallogenic stages.Results Six molybdenite samples from the S35 ore vein yield Re–Os isotopic isochron age of(214.9±5.2)Ma(MSWD=0.77),with model ages ranging from(192.3±2.9)Ma to(223.4±3.2)Ma.K–feldspar samples from F5 ore vein yield Ar–Ar weighted plateau age of(95.22±1.16)Ma and the isochron age of(95.10±4.57)Ma.Conclusions Molybdenite age suggests that the Mo mineralization in S35 vein occurred in Indosinian period,and K–feldspar age indicates a new tectono–magmatic–thermal event during the Middle Yanshanian,and this hydrothermal event may contribute to metallogenic activity of Au(Mo)deposit,which superimposed the molybdenum mineralization events of Indosinian.Combined with the results of hand samples and BSE images analysis,it is concluded that there are at least two episodes of hydrothermal event related to Au(Mo)mineralization in Dahu Au(Mo)ore district.