熊耳山地区东草沟金银矿床构造控矿特征与成矿规律研究

Study on Structure Ore-controlling Characteristics and Metallogenic Regulartiy of Dongcaogou Gold-Silver Deposit in Xiong’ershan Area

熊耳山矿集区地处秦岭造山带中东部,印支—燕山期地幔与地壳相互作用导致区内大规模的岩浆活动和构造运动,从而形成区内分布众多的不同期次和规模的贵金属及有色金属矿床。东草沟金银矿床是近年来在熊耳山矿集区新发现的一处金银矿床,目前处于勘探开发阶段。野外构造解析表明,东草沟金银矿床矿体严格受断裂控制,根据产状、运动学和变形特征,将矿区控矿断裂划分为构造破碎带(强构造变形带)和陡倾断裂。东草沟金银矿床构造与矿化时空关系研究表明:早、晚成矿阶段的控矿断裂特征明显不同。其中,早成矿阶段(印支末期—燕山早期)的控矿断裂为压性断层,显示出明显的韧—脆性变形特征,发育有S-C构造及构造片理化带,反映的构造应力场为近SN向挤压;晚成矿阶段(燕山中晚期)的控矿断裂表现为张性断层和脆性变形特征,矿脉具有典型的扩张性充填脉的特征,反映的构造应力场为近EW向引张。区内不同方向的控矿断裂是在近SN向挤压作用下形成的多方向复共轭断层(conjugate-conjugate faults)系,及由其派生的次级断裂,复共轭断层系统的组合式样(assemblage patterns)控制着区内矿体空间展布及式样。

The Xiong’ershan ore concentration area is located in the middle eastern part of the Qinling orogenic belt. Multi-stage tectonic activity leads to regional multi-level faults,among which the first-grade fault is a deepfault with multi-stage activity and structural inheritance characteristics,which controls the distribution oforiginal source of ore-forming materials and regional mineralization. The second-grade fault controls thedistribution of metallogenic belts.The third and fourth grade faults are the main ore hosting faults.The regionalextension and tectonic extension in Yanshanian period led to extensive magmatic activities,which providedimportant material and energy sources for mineralization.The interaction between the Yanshanian mantle and thecrust led to large-scale magmatic activities and tectonic movement,thus forming a large number of precious andnonferrous metal deposits of different stages and scales in the area.The Dongcaogou deposit is a new gold-silverdeposit discovered in the Xiong’ershan ore concentration area in recent years,which is still in the stage ofexploration and development. Field structural analysis shows that the orebody of the Dongcaogou deposit isstrictly controlled by faults. From the end of Indosinia to the early Yanshanian,the structure in the near EWdirection is dominant in this region,with minor NNE-near SN direction faults.Five stages of tectonic activitiesin the deposit were identified in this study,and their sequence and tectonic stress field are as follows:The firststage tectonic stress field is near SN compression,the second stage tectonic stress field is near EW compression,the third stage tectonic stress field is NW compression,these three stages fault are pre-mineralization structures,the fourth stage tectonic stress field is NNE compression,which is a fault structure in the syn-mineralization,and the late stage tectonic stress field is converted into extension due to stress relaxation.The fifth stage tectonicstress field is NE compression,which is a post-mineralization fault.According to the occurrence,kinematics anddeformation characteristics,the ore-control faults can be divided into structural fracture zone (strong structuraldeformation zone) and steep fault.The study of the time-space relationship between structure and mineralizationshows that the ore-controlling faults in the early and late ore-forming stages have obviously difference instructural characteristics.In the early ore-forming stage (late Indosinian early Yanshanian),the ore-controllingfaults are compressive faults and show obvious ductile brittle deformation where S-C structures and tectonicschistosity zones are developed,reflecting a tectonic stress field of nearly S-N compression. In the late oreforming stage (middle and late Yanshanian),the ore-controlling faults are characterized by tensile faults andbrittle deformation,and the ore veins are characterized by typical expansive filling veins,which suggested thattectonic stress field is nearly E-W oriented extension.The ore-controlling faults in different directions in the areaare multi-directional conjugate fault systems formed under the near S-N direction compression,and thesecondary faults derived from them.The assembly patterns of the compound conjugate fault system control thespatial distribution and pattern of ore bodies in the Dongcaogou Au-Ag deposit.