西秦岭八方山-二里河Pb-Zn矿区硅质岩的微区成分特征及演化

A study of micro-area compositional characteristics and the evolution of cherts from Bafangshan-Erlihe Pb-Zn ore deposit in Western Qinling Orogen

硅质岩以SiO2为主,并广泛发育于造山带内。激光Raman、SEM-EDS分析结果显示,研究区硅质岩微组构特征记录了造山作用、成矿作用和重结晶作用等的改造。SEM分析显示,研究区硅质岩中石英颗粒较小且呈紧密堆积,这些特征符合热水沉积快速结晶的特点。激光Raman分析结果中,石英颗粒自边缘向中心核部的拉曼特征峰(463cm-1)经高斯拟合(Gaussian Fitting)后尖锐程度逐渐递增,半高宽(FWHM)递减,反映了石英自身的重结晶作用。在石英颗粒边界与碳酸盐脉的接触部位,结晶程度和有序度自内向外呈递增趋势,反映了石英颗粒遭受了流体的影响,SEM分析结果中石英颗粒的絮状反应残余边界进一步支持了该结论。在SEM下,金属硫化物在裂隙和空隙中发生沉淀并呈线状和零星浸染状分布,与应力作用及杂质矿物有着密切的关系。另外,据硅质岩中的脉体穿插关系,指示西秦岭存在碳酸盐(铁白云石)热液→金属硫化物热液→硅质-碳酸盐(方解石)热液的多阶段流体演化,与东秦岭流体作用具有较好的相似性。

Chert,mainly composed of silica,are widely and stably distributed in the orogenic area. The results of Raman and SEM-EDS analyses of cherts indicate that the microfabric information of chert from the Bafangshan-Erlihe Pb-Zn ore deposit can be used to study the reconstruction of orogeny,of metallogenesis and of recrystallization. The SEM analysis show that the quartz grains in cherts are tiny and closely packed,which is in accordance with the characteristics of high nucleation rate of hydrothermal sedimentation. Despite of the high stability,the recrystallization of the quartz can be clearly proved by the Raman analysis showing that the FWHM value of the characteristic peak （463 cm^-1） of quartz after the Gaussian Fitting decreases from the rim to the core of the quartz grain,which indicates the increasing of crystallinity towards the core caused by the recrystallization of the quartz grain. For the quartz grains that were in contact with the carbonate vein,the crystallization degree of the quartz is increasing from the inner to the rim of the grain,implying that the quartz grains had been affected by the upper fluids. This is also supported by the SEM analysis showing that there are floccules at the interface between quartz and carbonate mineral. Some carbonate minerals were broken up and deformed under the stress during the orogenic activities,resulting in the fissures and holes filled up with metal sulphides. Under SEM,it can be seen that metal sulphides are distributed in the fissures and holes with linear and disseminated structures. In addition,in the interpenetration of different veins,there existed multiple stages of fluids evolution,which is similar to that in the Eastern Qinling orogen,with the order of carbonate （ankerite） fluids→metal sulphides fluids→siliceous-carbonate（calcite） fluids.