安徽池州许桥银矿地质特征及矿区深部找矿方向

Geological features of the Xuqiao silver ore deposit and downward ore-prospecting direction in the ore district,Chizhou,Anhui

许桥银矿床位于长江中下游成矿带安庆-贵池矿集区东南部,矿床银储量达到中型规模,成矿岩体为分水岭石英闪长岩,矿体主要呈似层状赋存于分水岭岩体北东侧奥陶系仑山组、汤山组地层层间裂隙中;矿石矿物主要为黄铁矿、闪锌矿、方铅矿、黝铜矿、黄铜矿、辉银矿、自然银,脉石矿物为石英、碳酸盐矿物;矿石组构以自形-他形晶结构、交代结构、稀疏浸染状构造和网脉状构造为主;围岩蚀变类型主要有硅化、碳酸盐化、矽卡岩化、绿泥石化等;许桥银矿床成矿作用经历了两个成矿期:热液期和表生期,热液期又可分为三个成矿阶段,即为矽卡岩阶段、石英-硫化物阶段及碳酸盐-硫化物阶段;成矿流体早期以岩浆热液为主、晚期混有大气降水的流体演化特征;成矿物质主要来源于岩浆热液,地层贡献了部分矿质;成矿温度为中低温(208～259℃),矿床类型为中低温热液银多金属矿床,并指明了矿区深部找矿方向。

The Xuqiao silver ore deposit is situated in the southeastem part of the Anqing-Guichi mining camp in the mid-lower Yangtze River reaches metallogenetic belt,with silver reserve up to a medium size,mineralization being host- ed in watershed quartz diorite, mainly stratoid ore body occurring in the interlayer fractures of the Ordovician Lunshan Formation and Tangshan Formation. Ore minerals include pyrite, sphalerite, galena, tetrahedrite, chalcopyrite, argentite, natural silver; gangue minerals are quartz and carbonate minerals; ore fabrics are substantially euhedral-anhedral, metaso- matic, sparsely disseminated and stockworked; wall rock alteration is dominated by silication, carbonatation, skarniza- tion and chloritization. The deposit has two mineralization epochs： hydrothermal epoch and supergene epoch, and the former is further divided into three stages, i.e., skarn stage, quartz-sulfide stage and carbonate-sulfide stage; ore-forming fluid is predominantly magmatic hydrothermal fluid in the early period, and joined by precipitation later. Ore-forming material is mainly derived from magmatic hydrothermal fluid, with some contribution from strata. Ore formed at mid- low temperature（208- 259℃）leading to a mid-low hydrothermal silver polymetallic deposit and giving clues for deep- seated ore prospecting in the ore district.