粤东宝山银(锑)矿床地质特征和成因

GEOLOGY AND GENESIS OF THE BAOSHAN SILVER(ANTIMONY)DEPOSIT IN EASTERN GUANGDONG

粤东宝山大型银(锑)矿床产于早侏罗世火山-沉积地层中,银、硫(锑)化物矿体呈脉状,沿下侏罗统金鸡组上段碳质页岩和粉砂岩的层间断裂中分布。矿床深部其青磐岩化蚀变,中部以黄铁矿化、硅化、碳酸盐化为主,上部以硅化为特征。矿区自西向东锑矿化减弱,银矿化增强,在垂直方向上,60 m 标高之上为锑矿化富集带,0m 标高以下为银矿化富集带。研究表明,区域早侏罗世火山-沉积地层可能是矿源层,矿床是与燕山中—晚期火山-次火山活动有关的浅成中-低温热液矿床。

The Baoshan large-sized(antimony)deposit in eastern Guangdong has Early Jurassic vol- canic-sedimentary rocks as host rocks.Silver and antimony contents of ore-bearing wall rocks are 3～2 orders of magnitude that of their abundances in identical rocks,and are 18～16 times their abundances in the same sorts of rocks in eastern Guangdong,showing characteristics of source bed.The Yanshanian volcanic-subvolcanic rocks include quartz porphyry,diabase and basalt, which contain relatively high silver,with the concentration coefficient of silver being 33,44 and 34 respectively.Volcanic activities brought such ore-forming materials as silver and antimony from the depth and caused activation and migration of ore-forming elements in wall rocks,which eventually entered hydrothermal solution. Wall rock alterations include silicification,pyritization,propylitization,sericitization,chlori- tization and carbonatization,showing vertical zonation.Silver mineralization is closely related to propylitization,pyritization and silicification,whereas antimony mineralization has to do with pyritization and silicification. There are altogether 21 orebodies in the ore district,which can be assigned to two groups trending NE-NNE and EW respectively.Silver and antimony mineralizations assume horizontal and vertical zoning.Horizontally,silver mineralization grows stronger from west to east,and things are just opposite for antimony mineraliztion;vertically,silver mineralization gets intensi- fied but antimony mineralization weakens from the shallow place to the depth. Siver and antimony migrate mainly in the form of sulfur complex.The favorable conditions for the precipitation of silver and antimony are pH 6.5～7.0,Eh-0.54 eV,t 160～290℃,P 160×10~5～175×10~5Pa,ore-forming depth 630～760m,salinity 2.23 wt%～19.04 wt%NaCl, and density 0.52～0.97g/cm^3.Sulfur,lead,oxygen and hydrogen isotopic compositions and REE partitioning show that metallogenic substances and ore-forming fluids came mainly from magma at depth,with the addition of wall rock materials and meteoric water.The ore deposit is a shallow-seated medium-low temperature volcanic-hydrothermal one,with filling as the major mineralization form.