江南造山带黄金洞金矿床成矿时限：构造-热年代学约束

The Jiangnan Orogen is one of the most important bases of gold resources in China. The ore genesis and ore-forming geodynamic background are still subjects of extensive debate, which is caused by the poorly constrained timing and duration of gold mineralization etc. Tectono-Thermochronology, which has become an efficient method to constrain the timing and duration of the ore-forming thermal event, can provide information about time, temperature, and structural control. Therefore, this project will focus on the timing and duration of the mineralization of the Huangjindong gold deposit, one of the most typical deposits in the Jiangnan Orogen. In order to find suitable minerals and samples for further dating, the associations and deformation of hydrothermal minerals will be studied by macroscopical mapping of structure- alteration- mineralization, mineral mapping at microscopic scale and analysis of micro-fabric. The timing of mineralization will be constrained by 40Ar/39Ar ages of hydrothermal muscovite and SHRIMP U-Pb ages of hydrothermal monazite and xenotime. The upper and lower limits of the timing of the mineralization will be constrained by the U-Pb ages of zircon from pre-mineralization dykes, zircon (U-Th)/He ages of ores and host rocks, and illite K-Ar ages of post-mineralization fault gouges. Finally, all the ages will be combined to constrain the timing and duration of gold mineralization, build thermal history of the deposit, and reveal the rules of the spatial-temporal evolution and distribution of the deposits. All these work will deepen our understanding on the metallogenic dynamics and ore genesis of the deposits in the Jiangnan Orogen, and provide theoretical basis for ore prospecting.

江南造山带是我国最重要的黄金资源基地之一，该区矿床成因与成矿地球动力学背景争议不断，其重要原因之一是成矿作用时限不清。构造-热年代学能够提供构造控制、时代与温度三重限定，已成为厘定成矿-热事件发生时代与持续时间最有效的方法。因此，本项目拟聚焦江南造山带最具代表性的黄金洞金矿床成矿时限这一关键科学问题，通过详细的构造-蚀变-矿化填图、矿物填图与显微组构分析，查明热液蚀变矿物组合与变形特征，优选测年对象；通过热液白云母40Ar/39Ar和热液独居石或磷钇矿U-Pb定年，厘定成矿作用年代；通过成矿前脉岩锆石U-Pb、岩矿石锆石（U-Th）/He和成矿后断层泥中伊利石K-Ar定年，限定成矿时代上、下限；多元信息综合约束金成矿-热事件的发生时代与持续时间，重建金矿床热历史，揭示复杂构造背景下金矿床的时空演化与赋存规律，深化对江南造山带成矿作用动力学和矿床成因的认识，为实现区域找矿新突破提供理论依据。

江南造山带是我国最重要的黄金资源基地之一，为深入理解该区矿床成因，项目聚焦金成矿作用时限与构造控制机理这一关键科学问题，选择具有代表性的黄金洞金矿床，通过系统的构造-年代学研究，取得以下认识：黄金洞金矿床赋存于新元古代浅变质岩系中，主要发育石英-硫化物脉型、石英角砾岩型与毒砂黄铁绢英岩型三种矿化样式；矿床内不发育受控于温度梯度的蚀变矿化与元素分带，成矿流体具有中低盐度和富CO2的特征，同位素数据指示成矿物质与流体为变质来源。区域一级控矿构造—NE-NNE向长沙-平江（长平）断裂控制区内金矿田的空间展布，并为深源含金流体上涌提供通道；受控于NE-NNE向泥湾、长垄与坑上二级断裂控制，矿床内产出多个NE-NNE向成矿廊带，廊带内发育受控于紧闭褶皱和逆断层的近EW-NWW向早期贫矿石英脉；NNE-NE向控矿断裂左行走滑活动过程中，成矿廊带不同块体间发生旋转变形，贫矿石英脉能干性强，在构造应力作用下极易发生碎裂变形，超压流体亦可导致贫矿石英脉水力致裂；大规模角砾岩化致使成矿系统渗透率急剧升高，含金流体随之注入；构造-流体压力波动诱发流体相分离进而导致可见金在构造裂隙和角砾胶结物中沉淀，硫化作用导致金伴随黄铁矿和毒砂共同沉淀。热液白云母40Ar/39Ar年龄指示成矿早期贫矿石英脉形成略早于400Ma，金成矿发生于约400Ma或略晚，后期有构造热事件叠加。综上所述，黄金洞金矿床形成于转换挤压构造背景下，矿体形成严格受逆断活动控制，成矿物质为变质来源，具有典型造山型金矿床特征；受控于褶皱或逆断层的早期贫矿石英脉是有利找矿靶区。