湘东北万古金矿床控矿构造特征与控矿规律研究

Characteristics of Ore-controlling Structures of Wangu Gold Deposit in Northeastern Hunan Province

湘东北位于江南造山带中部,呈典型的盆岭构造格局。该盆岭省由北东向深大走滑断裂、花岗岩山岭和红层盆地组成,其中产有大型–超大型规模的万古金矿。该矿床赋存在新元古界冷家溪群层间破碎带内,矿石类型主要为含矿石英脉型和蚀变岩型,其次为构造角砾岩型。万古矿区发育北西(西)向和北东向两组断裂,其中北西(西)向断裂为赋矿构造。通过分析华南板块的构造演化,认为万古金矿区的北东向断裂与燕山期古太平洋板块俯冲与后撤有关,而北西(西)向断裂可能形成于加里东–印支期,但在燕山期重新活化并成为容矿构造。区域航磁异常、CSAMT法地球物理探测和深部钻探工作进一步显示,低阻的北西(西)向含矿断裂可能延伸至万古矿区外围深部的黄浒洞组,且沿该断裂带赋存的矿体具侧伏规律,说明万古金矿区深部仍有找矿潜力。万古金矿区–金井一带有较大的航磁正异常和稳定的低重力场,其深部的黄浒洞组地层中有局部强磁异常,推测该区深部可能存在较大的隐伏岩体,该岩体侵位时的热量可为含矿流体的迁移提供能量。

The central Jiangnan Orogenic Belt in northeastern Hunan province shows typical basin and range characteristics. This basin and range province, which is host to the super-large Wangu gold deposit, is composed of NE-trending large strike-slip faults, granitic plutons and red-bed basins. The Wangu gold deposit is hosted in the interlayer fracture zone in the Neoprotozoic Lengjiaxi Group. The ore types are mainly auriferous quartz veins and altered rock type with minor tectonic breccia type. NW（W）- and NE-trending faults were recognized in the orefield, and the NW（W）-trending faults are the gold-bearing structures. Integrating the tectonic evolution of South China and comparison of the Wangu gold deposit with other lode-type gold deposits, it is inferred that the NE-trending faults were related to the subduction and rollback of the paleo-Pacific plate during the Yanshanian. The NW（W）-trending faults might have been formed during the Caledonian-Indosinian, and were reactivated during the Yanshanian, thus accommodated the ores. Aeromagnetics, CSAMT and deep drilling indicate that the NW（W）-trending faults with low resistivity extend to the depth of the Huanghudong Formation outside of the Wangu orefild. The lateral extension of orebodies in the NW（W）-trending faults shows the potential of deep prospection in the Wangu gold deposit. Combined with the strong local magnetic anomalies in the Huanghudong Formation, the large positive aeromagnetic anomalies and the low gravity field in the Wangu deposit and the Jinjing district, we suggest a large concealed intrusion possibly provided energy for the transportation of gold-bearing fluid.