摘要
粤北大宝山铜多金属矿床一直存在燕山期岩浆热液成因和海西期火山喷流成因之争,争议的焦点在于块状、似层状硫化物矿体的成因。本文在全面开展矿区地质调查和钻探查证的基础上,对块状、似层状和脉状硫化物矿石中的黄铁矿和磁黄铁矿开展EPMA和LA-ICP-MS原位分析。测试结果表明,不同产状黄铁矿的平均分子式相似,分别为FeS_(1.98)、FeS_(1.99)和FeS_(1.98),似层状和脉状硫化物中磁黄铁矿的平均化学式为Fe_(0.886)S和Fe_(0.874)S,属形成温度相对较低单斜磁黄铁矿。与花岗岩岩浆热液标型黄铁矿相比,不同产状的黄铁矿和磁黄铁矿中Co、Ni、Mn、Se和Ge等元素以类质同象形式赋存,它们含量较低但稳定,Cu、Pb、Zn、Ag、Bi和Tl及Ga主要以微细矿物子晶形式存在,其含量丰富,但变化明显。从块状、似层状到脉状硫化物矿体,黄铁矿和磁黄铁矿中Co、Zn和Se的含量及Co/Ni值降低,而Cu、Pb、Ag、Bi等元素的含量明显升高。结合矿区次英安斑岩的产状和含矿性特征表明,大宝山矿床块状、似层状和脉状硫化物矿体都是次英安斑岩深部岩浆房产出的含矿流体在不同赋矿环境中的产物。
There has long existed controversy concerning the metallogenic mechanism of the Dabaoshan Cu-polymetallic deposit.The debate focuses on the metallogenic mechanism of massive and stratoid sulfide ores as to whether they were formed by magmatic hydrothermal fluids related to the Yanshanian granotoid or VMS in the Hercynian period.Based on detailed geological survey of the orefield and drilling verification,the authors investigated in-situ trace element values of pyrite and pyrrhotite in massive,stratoid and veined sulfide ores by EPMA and LA-ICP-MS.The data show that the average molecular formulae of pyrites from different modes of occurrence of sulfide ores are FeS_(1.98),FeS_(1.99 )and FeS_(1.98),the average molecular formula of the pyrrhotite in stratiform sulfide ores is Fe_(0.886)S,and that in veins is Fe_(0.874)S,suggesting relatively low temperature mpo.Compared with things of typomorphic pyrite formed by granitic hydrothermal fluids,Co,Ni,Mn,Se and Ge are low in content but steady as isomorphism in pyrite and pyrrhotite from different modes of occurrence of sulfide ores.The values of Cu,Pb,Zn,Ag,Bi,Tl and Ga are rich but variable,and they formed daughter crystals in pyrite and pyrrhotite.From massive and stratoid to veined sulfide ores,the Co,Zn,Se values and Co/Ni ratios decrease,while the Cu,Pb,Ag and Bi values increase in both pyrite and pyrrhotite.In combination with the occurrence and mineralization characteristics of sub-dacite porphyry,the authors consider that the massive,stratoid and veined sulfide ores in the Dabaoshan deposit were produced by the same metallogenic hydrothermal fluids in different environments,expelled from deep magma chamber of the sub-dacite porphyry.