1.东华理工大学核资源与环境国家重点实验室，江西 南昌 330013
2.东华理工大学地球科学学院，江西 南昌 330013
3.东华理工大学江西省放射性地学大数据技术工程实验室，江西 南昌 330013
作者简介 About authors
蚀变岩型矿石是热液型金矿床中重要的矿石类型，其形成与水岩反应密切相关。江南造山带黄金洞金矿中的蚀变岩型矿石多发育在褪色化蚀变带中，目前其形成机制尚不清楚。野外勘查、岩相学观察和TIMA分析表明，蚀变带中最主要的特征是广泛发育菱铁矿、绢云母和隐晶质石英。蚀变岩型矿石局部可见较多硫化物，与含金石英脉中的硫化物具有相似的化学成分，说明为同一期流体作用的产物。部分硫化物切穿碳酸盐矿物，说明褪色化蚀变形成于成矿前。TIMA和μ-XRF分析表明，蚀变带发生硅化和绢云母化，且Fe聚集成点状。因此，推测成矿前的水岩反应形成大量菱铁矿斑点，为成矿提供良好的化学圈闭。成矿期含金流体与菱铁矿发生化学反应，通过硫化作用促进金的沉淀，为黄金洞金矿蚀变岩型矿石的成矿机制。
关键词：热液型金矿;蚀变岩型矿石;褪色化蚀变;菱铁矿;硫化物;成矿机制;江南造山带
Keywords：hydrothermal gold deposit;altered rock type ore;bleaching alteration;siderite;sulfide;metallogenic mechanism;Jiangnan orogenic belt
本文引用格式
1.新元古代小木坪组第二段；2.新元古代小木坪组第一段；3.第四系；4.倒转向斜；5.倒转背斜；6.金矿脉；7.断裂；8.取样位置
图3黄金洞金矿矿脉、褪色化蚀变带手标本和显微照片
（a） 与含矿石英脉相邻的褪色化蚀变带；（b） 褪色化蚀变带的颜色变化；（c） 碳酸盐—石英脉两侧对称的褪色化蚀变带；（d） 含金蚀变岩；（e） 黄铁矿切穿菱铁矿；（f） 浸染状黄铁矿位于菱铁矿附近；（g） 溶蚀的菱铁矿边缘局部被石英胶结；（h） 碳酸盐—石英脉由绢云母、方解石、石英、绿泥石和硫化物组成；（i） 碳酸盐—石英脉被含毒砂、黄铁矿的矿脉横切Apy-毒砂；Py-黄铁矿；Sd-菱铁矿；Sph-闪锌矿；Qtz-石英；Cc-方解石；Ser-绢云母
Fig.3Hand specimens and photomicrograph of the gold veins and fading alteration zone of the Huangjindong gold deposit
有些矿物无法被识别的原因可能是：（1）薄片抛光质量不合格；（2）某些矿物的谱峰相当接近，无法被能谱检测器完全分离，从而产生光谱叠加造成干扰。未识别出的矿物中有一半以上粒径小于1 µm。
电子探针和激光剥蚀等离子质谱仪分析均在东华理工大学核资源与环境国家重点实验室进行。电子探针的试验仪器为JEOL JXA-8120型电子探针。分析条件如下：加速电压为20 kV，电流为15 nA，束斑直径为1~2 μm，峰值计数时间为20 s，背景时间为10 s。激光剥蚀等离子质谱仪分析采用以高能量准分子激光器为基础的NWR193HE智能激光剥蚀系统。分析的主微量元素包括Zn、Cu、Cd、Fe、Mn、S、Ni、Te、As、Ag、Pb、Co、Au、Se、Sb、W、Tl和Bi。
图4利用TIMA对碳酸盐—石英脉和褪色化蚀变带进行的矿物鉴定和填图
Fig.4Mineral identification and mapping of carbonate-quartz vein and bleaching alteration zone used by TIMA
野外和钻孔编录可观察到褪色化蚀变带在石英脉两旁呈对称分布，在此基础上，利用TIMA在该样品中观察到2个蚀变带，碳酸盐—石英脉近端的蚀变带为硅化，远端的蚀变带为绢云母化。近端硅化蚀变带以石英（59%）、钠长石（11%）和菱铁矿（8%）为主，菱铁矿主要赋存于碳酸盐—石英脉与含金蚀变岩的接触部位。远端绢云母化蚀变带由绢云母（65%）、石英（17%）、钠长石（9%）以及少量菱铁矿（4%）和绿泥石—斜绿泥石（2%）组成。等粒径石英—绢云母—钠长石组合为蚀变板岩的基质。
图5碳酸盐—石英脉和褪色化蚀变带的μ-XRF元素填图
（a）~（k） μ-XRF元素填图；（l） 对应的薄片照片
Fig.5μ-XRF element mapping of carbonate-quartz vein and bleaching alteration zone
表1石英脉中黄铁矿和黄铜矿的电子探针分析结果
Table 1 EPMA analysis results of pyrite and chalcopyrite from quartz vein（%）
注：“-”代表低于检测限
表2蚀变围岩中黄铁矿和黄铜矿的EPMA元素值
Table 2 EPMA element values of pyrite and chalcopyrite from altered surrounding rock（%）
注：“-”代表低于检测限
图6含金蚀变岩和含金石英脉中黄铁矿和黄铜矿的EPMA和LA-ICP-MS分析结果
Fig.6EPMA and LA-ICP-MS analysis results of pyrite and chalcopyrite from Au-bearing alteration rock and Au-bearing quartz veins
表3石英脉中黄铁矿的LA-ICP-MS分析结果
Table 3 LA-ICP-MS analysis results of pyrite from quartz vein（×10-9）
注：“-”代表低于检测限
表4蚀变围岩中黄铁矿的LA-ICP-MS分析结果
Table 4 LA-ICP-MS analysis results of pyrite from altered rock（×10-6）
（1）黄金洞金矿床蚀变岩型矿石主要赋存于含菱铁矿的褪色化蚀变带中，褪色化主要由碳酸盐化、绢云母化和硅化引起，沿成矿前引起褪色化的碳酸盐—石英脉对称分布，颜色由绿灰色转变为浅黄—灰色。蚀变具有分带性，从碳酸盐—石英脉的近端到远端分别为硅化和绢云母化。
（2）菱铁矿中Mg、Fe和Mn元素聚集呈点状。部分菱铁矿被含金硫化物横切，局部被石英溶蚀，表明褪色化蚀变发生在矿化前，可能是富CO2流体与围岩反应的结果。
（3）菱铁矿与含金流体发生化学反应，大幅降低了流体中S含量，从而沉淀黄铁矿和黄铜矿等含金硫化物。菱铁矿为金矿化提供了理想的化学圈闭，通过硫化作用沉淀金。
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湘东北地区陆内构造—岩浆活化及其对金成矿作用的控制
热液金矿床围岩蚀变特征及其与金矿化的关系
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利用微区XRF技术的大洋固体矿产成分快速无损检测
江南古陆某些金矿床成因讨论
江南造山带黄金洞金矿床成矿机制：矿物形成环境与金成矿物理化学条件制约
湘东北黄金洞金矿床微量元素、稀土元素特征及其地质意义
湘东北大洞—万古地区金矿构造成矿定位机制的初步研究
应用TIMA分析技术研究Alum页岩有机质和黄铁矿粒度分布及沉积环境特征
湘东北连云山二云母二长花岗岩的年代学和地球化学特征：对岩浆成因和成矿地球动力学背景的启示
湘西合仁坪钠长石—石英脉型金矿床围岩蚀变及质量平衡
黄金洞金矿位于湘东北地区长沙—平江断裂东侧，成矿地质条件优越.已探明金储量为80 t，金品位为 4×10-6~10×10-6（平均值为5×10-6），包括阳山庄、金枚和金塘等矿区（图2）（Xu et al.，2017；Deng et al.，2020）.新元古代冷家溪群NW-NWW向小木坪组是主要的含矿围岩，根据岩性可划分为2段：第一段为层状钙质板岩，夹有粉砂质板岩、条带状板岩、变质细砂岩和绢云母板岩；第二段为层状砂质板岩，含粉砂质板岩、变质粉砂岩、绢云母板岩、条带状板岩、斑点状板岩、千枚状板岩和变质细粒砂岩，是含金矿脉的主要赋存层位（Deng et al.，2020）. ...
1.新元古代小木坪组第二段；2.新元古代小木坪组第一段；3.第四系；4.倒转向斜；5.倒转背斜；6.金矿脉；7.断裂；8.取样位置 ...
黄金洞金矿床发育有NWW和NE向2组断裂.其中，NWW向断裂与地层产状相近，是主控矿构造.该组断裂可能形成于早古生代，中生代晚期在区域构造应力的作用下重新活化（Zhou et al.，2021；肖拥军等，2004）.NE向断裂切割NWW向断裂，如：长平一级断裂和泥湾二级断裂等.此外，还发育有一系列NWW-EW向倒转褶皱，控制着矿体的分布.矿体多向北倾斜，占现有储量50%以上的重要矿脉向南倾斜（Zhang et al.，2018，2019）.该区未见岩浆岩出露，离矿区最近的侵入体是位于西南方向约12 km处形成于约142 Ma的连云山花岗岩（许德如等，2017）. ...