加拿大萨德伯里奈恩( Nairn) 铜多金属矿地球化学特征及意义

[摘 要] 加拿大奈恩(Nairn)工作区位于萨德伯里(Sudbury)镍铜矿集区南西方向约50 km,工作区内的矿化类型可划分两类:淤产于辉长岩中的铜镍矿化和于产于石英角砾岩中的铜矿化。两种矿石的微量元素和稀土元素特征较为相似, 高场强元素中富集Th-Zr-Hf 而相对亏损Nb-Ta 等,大离子亲石元素中富集Rb-U-Pb 而相对亏损Ba-P-Ti 等,稀土元素相对富集轻稀土,轻稀土元素分馏程度明显,而重稀土元素分馏程度不明显,铈异常不明显,而铕异常变化较大,总体上表现为负异常。上述特征暗示其物质来源可能相似,结合其矿物组合和本区围岩特征来看, 铜镍矿石主要与中-基性岩浆有关,而石英角砾岩的铜矿化主要与后期的岩浆热液有关,表明两种矿化类型主要与本区岩浆的结晶分异作用有关,早期的高温铜镍硫化物随辉长岩中硅酸盐矿物的结晶而后生成,晚期的含矿热液沿构造产生的断层破碎带迁移并最终充填在构造裂隙中。从奈恩矿区成矿特征来看,本区辉长岩墙与上伏围岩的接触部位,特别是构造发育或相互交汇处将为最有利的成矿部位。

Geochemical Characteristics of the Nairn Copper Polymetallic Deposit,Sudbury,Canada and Their Significance

Abstract:The Nairn working area is located about 50km to the southwest of the Sudbury Cu-Ni ore concentration area in Canada. The mineralization in this area is dominated by copper-nickel mineralization within gabbros and copper mineralization within quartz breccias. Both of them have the similargeochemical characteristics of high content of Th,Zr,Hf and relatively lower content of Nb,Ta and other HFSE,high content of Rb-U-Pb and relativelylower content of Ba,P,Ti and other LILE. The REE exhibits right-dipping chondrite normalized patterns with unobvious Ce anomalies,negative Eu anomalies and with obvious fractionation of LREE and indistinct fractionation of HREE. These features imply that they originate from the similar source related to the magma activity and their crystal fractionation. The copper-nickel mineralization within gabbros is mainly related to mafic magma,and the copper mineralization within quartz breccias is mainly related to magmatic hydrothermal fluids. Copper-nickel sulfides formed from high temperature magma after crystallization of silicate minerals in gabbros in the early stage,and the magmatic hydrothermal fluids formed in the later stage and shifted along fault fracture zones and filled in structural fissures. Based on the metallogenic features in the Nairn working area,the contacts between gabbro dyke and quartzites,especially the places where structures developed well or faults intersect,are considered to be the most favorable mineralization loci.