湖南黄金洞金矿床白钨矿Sm-Nd年龄及其地质意义

Scheelite Sm-Nd age of the Huangjindong Au deposit in Hunan and its geological significance

黄金洞金矿床是江南造山带上重要的金矿产地之一,矿体赋存在新元古代的浅变质岩中,受东西向-北西西向构造的严格控制。多年来,黄金洞金矿床的成矿年龄一直存在着争议。通过对黄金洞金矿区的白钨矿开展详细的野外调查、岩相学观察和Sm-Nd同位素分析,在147Sm/144Nd-143Nd/144Nd图解中获得白钨矿的等时线年龄为(129.7±7.4) Ma (MSWD=1.0),对应的εNd(t)值为-8.21~-8.68。结合黄金洞矿区白钨矿与含金硫化物的交切关系观察、以及前人的成矿年代学和矿物学研究成果,认为白钨矿的等时线年龄可作为黄金洞金矿床的成矿年龄。白钨矿的εNd(t)值大于赋矿地层新元古界冷家溪群和湘东北早白垩世花岗岩,但小于新元古界仓溪岩群,表明白钨矿中的Nd部分来自新元古界冷家溪群和(或)湘东北早白垩世花岗岩,部分来自新元古界仓溪岩群。综合前人的研究,认为在江南造山带的金锑钨成矿作用中,新元古界为矿源层,区域变质作用和岩浆作用共同促进了金等成矿物质的活化,构造活化为含矿热液的运移和沉淀提供了通道和空间。

The Huangjindong gold deposit is one of the most important Au reserve in the Jiangnan Orogenic Belt.Its orebodies are strictly controlled by a series of E-to WNW-trending faults developed in low-grade metamorphic Neoproterozoic strata. However, the mineralization age of the Huangjindong deposit has not been constrained.Detailed field surveys, petrographic observations and Sm-Nd isotopic analyses have been carried out on scheelites in the Huangjindong deposit area. The scheelites yield an isochron age of 129.7±7.4 Ma(MSWD=1.0) on the 143Nd/144Nd versus 147Sm/144Nd plot, with corresponding εNd(t) values varying from -8.21 to -8.68. Based on the crosscutting relationship of the scheelite vein and Au-bearing sulfide vein in the Huangjindong deposit, and the previous studies on geochronology and mineralogy, the isochron age of scheelites is considered to be the mineralization age of the Huangjindong gold deposit. The εNd(t) values of scheelites are higher than those of the ore-bearing Neoproterozoic Lengjiaxi Group and early Cretaceous granitoids in northeastern Hunan but lower than those of the Neoproterozoic Cangxiyan Group, indicating that Nd in the scheelites partly originate from the Neoproterozoic Lengjiaxi Group and/or the early Cretaceous granitoids in northeastern Hunan, and partly from the Neoproterozoic Cangxiyan Group. Combined with previous research, ore materials of the Au-Sb-W deposits in the Jiangnan Orogenic belt are interpreted to be sourced from the Neoproterozoic strata owing to regional metamorphism and magmatic activities are interpreted to have facilitated the reactivation of ore-forming materials such as Au.Structural reactivation was interpreted as the source of channels and space for ore-fluids during the Au-Sb-W ore-forming process in the Jiangnan Orogenic Belt.