广东河台金矿田糜棱岩磁组构对剪切带变形与成矿的约束  

Characteristics of mylonite magnetic fabrics and constraint on the relationship between the shear zone deformation and mineralization

作　　者：李康 焦骞骞 许德如 张胜印 常华诚 戴家润 LI Kang;JIAO Qianqian;XU Deru;ZHANG Shengyin;CHANG Huacheng;DAI Jiarun(Faculty of Land Resource Engineering,Kunming University of Science and Technology,Kunming,Yunnan 650093,China;State Key Laboratory for Nuclear Resources and Environment,East China University of Technology,Nanchang,Jiangxi 330013,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093 [2]东华理工大学,核资源与环境国家重点实验室,江西南昌330013

出　　处：《地质学报》2024年第6期1757-1775,共19页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41902086);云南省重大科技项目(编号202202AG050006)联合资助的成果。

摘　　要：河台金矿田是广东省内规模最大的金矿,由于金矿床都产于糜棱岩带中,因而被认为是典型的与剪切带有关的金矿。然而,对于Au矿化与剪切带变形条件之间的关系目前仍不十分清楚。高村和云西是河台金矿田两个代表性的金矿床,分别受ML11和ML9两条剪切带的控制。本文在对两条剪切带中的含矿和无矿糜棱岩的变形特征进行野外调查和室内岩(矿)相学观察的基础上,分别开展岩石磁学和磁化率各向异性(AMS)特征研究。糜棱岩x-T曲线显示了磁黄铁矿的居里温度,结合磁滞回线、等温剩磁(IRM)以及矿相学特征,表明河台金矿田糜棱岩几乎不含磁铁矿,载磁矿物主要为黑云母和磁黄铁矿,但是磁黄铁矿的贡献要远大于黑云母。两条糜棱岩带中不含矿糜棱岩的平均磁化率K_(m)<500×10^(-6)(SI)、磁化率各向异性度P_(j)、椭球体形状参数T、磁面理F和磁线理L没有明显差别。并且形成两条剪切带的主应力方向也近于一致,最大主应力方向σ_(1)(K_(3))为近水平NNW-SSE向,最小主应力σ_(3)(K_(1))为NEE-SWW向,倾伏角较缓。运动学涡度W_(k)值也近似,在0.12~0.65之间,小于0.71。上述特征暗示两条含金剪切带都是在印支期NNW-SSE向近水平的强烈挤压作用下形成的,其中发育的糜棱岩为S型和SL型构造岩,具有强烈压扁的特征,并且在剪切变形过程中纯剪切作用所占的比重要明显大于简单剪切。然而,两条剪切带中含矿糜棱岩与无矿糜棱岩的AMS特征有明显的区别。含矿糜棱岩的K_(1)近于直立,且K_(m)>500×10^(-6)(SI)和P_(j)值都明显大于无矿糜棱岩。因此,糜棱岩的变形强度与含矿性具有一定的正相关关系,而在燕山期叠加的脆韧性变形使得最大磁化率主轴(即最小主应力轴)变陡,更有利于热液的运移和最终成矿。The Hetai goldfield with gold deposits strictly hosted by mylonite zones are considered to be a typical gold mineralization example related to ductile-shear deformation and have the largest gold reserves in the Guangdong Province.However,the shear deformation conditions versus the gold mineralization remain unclear.The Gaocun and the Yunxi gold deposits confined to ML11 and ML9 mylonite zone respectively,are the significant gold producers in the goldfield.The magnetic petrology and anisotropy of magnetism susceptibility(AMS)of the barren and auriferous mylonite in the shear zones were studied after macroscopic deformation and petrography characteristic observation.The x-T curves of mylonite show the Curie temperature of pyrrhotite,in combination with the hysteresis loops,isothermal remnant magnetism(IRM)and petrography characteristics,indicating biotite and pyrrhotite are the dominant magnetic bearing minerals of the mylonite with no magnetite,and the contribution of pyrrhotite is much larger than the biotite in Hetai goldfield.Therefore,the AMS characteristics are effective in showing the deformation of the shear zones.The barren mylonite in ML11 mylonite belt(Gaocun deposit)has a similar mean magnetism susceptibility value K_(m)(<500×10^(-6)(SI)),corrected anisotropy degree Pj,ellipsoid shape factor T,magnetism foliation F and lineation L with the ML9 mylonite belt(Yunxi deposit).Moreover,both the shear zones show consistent orientation of principle stress,nearly horizontal NNW-SSE striking maximum principle stress σ_(1)(K_(3))and steep dip NEE-SWW striking minimum principle stress σ_(3)(K_(1)).Kinematic vorticity of two shear zones are also undistinguishable,varying from 0.12 to 0.65,i.e.less than 0.71.These characteristics suggest that both the shear zones in the Hetai goldfield were subjected to Indosinian NNW-SSE trending severe compression which resulted in the mylonite as the S and SL tectonites with intense oblate stain ellipsoid,and the pure shear is dominant in the shear deformation.However,the AMS

关 键 词：磁化率各向异性(AMS) 显微构造 糜棱岩x-T曲线 运动学涡度 河台金矿 

分 类 号：P618.51[天文地球—矿床学]