西秦岭甘肃徽县大石湾钴锰矿床地质特征及成因

Geological characteristics and genesis of the Dashiwan-cobalt manganese deposit in Huixian County,Western Qinling mountains

甘肃徽县大石湾钴锰矿床位于西秦岭造山带云台-迷坝成矿带东段,矿体赋存于上志留统卓乌阔组第4段灰岩夹硅质岩建造、灰岩-硅质岩建造2套含矿建造中。为进一步指导该地区的找矿工作,通过开展大石湾钴锰矿区建造构造专项填图,结合探槽揭露和老硐编录,分析建造构造与成矿之间的关系,对地质特征、成矿规律进行了总结,认为矿床成因类型为沉积-改造型钴锰矿。研究结果表明,卓乌阔组第4段硅质岩与灰岩接触带(硅钙面)为主要赋矿空间,其次为灰岩-硅质岩建造中层间断裂带。主要控矿构造方向为近EW向;矿床的成矿具有多期次的特点,与多期次的构造运动相对应;加里东晚期是该矿床最主要的初始富集成矿期,印支期是该矿床一个重要的构造期,该期近EW向的挤压逆冲推覆构造对原始沉积层进行叠加改造;燕山期NE向、NNE向压扭性断裂对早期含矿地质体截切错动,并为后期钴锰再次淋滤富集提供了有利空间,为成矿期后构造单元,控制钴锰最终成矿的赋存状态。

The Dashiwan cobalt-manganese deposit in Huixian County is located in the eastern section of the Yuntai-Miba mineralization belt in the West Qinling orogenic belt.The ore body occurs in two sets of ore bearing formations:the limestone intercalated siliceous rock formation and the limestone siliceous rock formation in the fourth segment of the Upper Silurian zhuowukuo Formation.In order to further guide the exploration work in the region,a special mapping of the construction structure of the Dashiwan cobalt-manganese mining area was carried out,combined with trench exploration and old cave logging.The relationship between the construction structure and mineralization was analyzed,and the geological characteristics and mineralization laws were summarized.It is believed that the genetic type of the deposit is a sedimentary reformed cobalt-manganese deposit.The research results indicate that the contact zone between siliceous rocks and limestone in the fourth segment of the zhuowukuo Formation(siliceous calcium surface)is the main ore-forming space,followed by the interlayer fault zone in the limestone siliceous rock formation.The main direction of the ore control structure is in the near EW direction.The mineralization of ore deposits has the characteristic of multiple stages,which corresponds to multiple stages of tectonic movements;The late Caledonian period was the main initial enrichment stage of this deposit,while the Indosinian period was an important tectonic period.During this period,the nearly EW trending compression thrust nappe structure superimposed and transformed the original sedimentary layers;The NE and NNE trending compressional and torsional faults during the Yanshanian period cut and dislocated the early ore-bearing geological bodies,providing favorable space for the subsequent leaching and enrichment of cobalt and manganese,and controlling the occurrence state of cobalt and manganese mineralization in the post mineralization tectonic units.