Information on abundance and distribution of platinum\|group elements (PGE) in peridotite from ophiolite is relevant to understand the nature and evolution of the upper mantle. The ophiolite suite outcropping along th...Information on abundance and distribution of platinum\|group elements (PGE) in peridotite from ophiolite is relevant to understand the nature and evolution of the upper mantle. The ophiolite suite outcropping along the famous suture zone of Yarlung Zangbo River, Tibet, has attracted wide attention of geologists both in China and abroad. The Dagzhuka ophiolite of in the suture zone is thought to display a complete ophiolitic sequence. The peridotite from the Dazhuka ophiolite is composed of fairly fresh or unaltered lherzolite, harzburgite and minor dunite which are the upper mantle residuum formed by 15%～35% partial melting. In this paper we have mainly studied the abundance and distribution of PGE in the harzburgites and lherzolites. The harzburgites and lherzolites preserve total PGE contents of 28 37×10 -9 ～50 67×10 -9 respectively higher than Primitive mantle or the peridotite from some typical ophiolites and Alpine. They all have fractionated chondrite\|normalized PGE patterns with positive slopes from Ir to Pd (Fig.1), and Pd/Ir=1 13～2 40>1, Pd/Rh=2 23～7 49>1, and Pd/Pt=0 26～1 16 (average 0 67) higher than Primitive mantle (1 11, 2 35, 0 57) or CI\|chondrite (1 01, 2 73, 0 53). Consequently, the Dagzhuka peridotite are PGE\|enriched, but otherwise possess residual characteristics arising from a minimum of 15% partial melting. It is suggested that mantle residuum by partial melting have low total PGE contents, fractionated chondrite\|normalized PGE patterns with negative or slightly flat slopes from Ir to Pd, and Pd/Ir<1. But, the total PGE contents, chondrite\|normalized PGE patterns and Pt/Ir, Pd/Rh and Pd/Pt values of the Dagzhuka peridotite are completely inconsistent with a residual origin. Partial melting would have partitioned all sulfide in the source into the melt. In fact, no sulfide or silicate melt remained in the Dagzhuka peridotite. Therefore, PGE in Dagzhuka peridotite are not present in sulfides. The PGE\|enrichment and fractionation of the Dagzhuka peridotites seem to arise from mantle metasomatism of melts/fluid enrich incompatible elements include Pt and Pt, but not from residual or percolation of sulfides. The enrichment of Cs, Rb, Ba, Th, U and LREE in Dagzhuka peridotite also give a hint of the mantle metasomatism. The abundance and distribution of PGE in the peridotite from the Dagzhuka ophiolite show the nature and evolution of the Dagzhuka upper mantle are distinctive.展开更多
岩浆型Ni—Cu—PGE(platinum group elements,铂族元素)硫化物矿床是重要的铜镍矿床类型,探讨该类型矿床产出环境,成矿作用,矿床成因机制具有重要意义。本文通过对该类型矿床时空分布规律,矿床成矿过程,成矿理论,勘查技术等方面入手,搜...岩浆型Ni—Cu—PGE(platinum group elements,铂族元素)硫化物矿床是重要的铜镍矿床类型,探讨该类型矿床产出环境,成矿作用,矿床成因机制具有重要意义。本文通过对该类型矿床时空分布规律,矿床成矿过程,成矿理论,勘查技术等方面入手,搜集大量资料,综述该类型矿床在成岩成矿年代学、地球化学特征、矿床形态、成矿理论和成矿判别标志等方面的研究现状,结果表明:岩浆型Ni—Cu—PGE硫化物矿床在容矿岩石、成矿作用方式或主要金属组份、成矿构造环境等特点具有不同分类方式,并且硫化物(矿层)的分布都具有重力分异的特点;在时空分布规律方面国外Ni—Cu—PGE硫化物矿床主要形成时间是在中元古代以前,而中国主要形成时间是在中元古代以后;其中早古生代晚期(390~430 Ma)的该类矿床目前仅发现于中国,以夏日哈木超大型矿床为代表;成矿模式存在"岩浆通道成矿"和"小岩体成大矿"之争,二者在成矿位置、岩浆上侵方式、外来地壳硫的加入存在差异;依据全岩m/f与Mg~#比值判定岩体含矿性,结合铂族比值、磁铁矿的(Ni+Cr)/(Si+Mg)比值、磁铁矿Ti含量等可作为该类型矿床勘查评价的重要参考指标。展开更多
文摘Information on abundance and distribution of platinum\|group elements (PGE) in peridotite from ophiolite is relevant to understand the nature and evolution of the upper mantle. The ophiolite suite outcropping along the famous suture zone of Yarlung Zangbo River, Tibet, has attracted wide attention of geologists both in China and abroad. The Dagzhuka ophiolite of in the suture zone is thought to display a complete ophiolitic sequence. The peridotite from the Dazhuka ophiolite is composed of fairly fresh or unaltered lherzolite, harzburgite and minor dunite which are the upper mantle residuum formed by 15%～35% partial melting. In this paper we have mainly studied the abundance and distribution of PGE in the harzburgites and lherzolites. The harzburgites and lherzolites preserve total PGE contents of 28 37×10 -9 ～50 67×10 -9 respectively higher than Primitive mantle or the peridotite from some typical ophiolites and Alpine. They all have fractionated chondrite\|normalized PGE patterns with positive slopes from Ir to Pd (Fig.1), and Pd/Ir=1 13～2 40>1, Pd/Rh=2 23～7 49>1, and Pd/Pt=0 26～1 16 (average 0 67) higher than Primitive mantle (1 11, 2 35, 0 57) or CI\|chondrite (1 01, 2 73, 0 53). Consequently, the Dagzhuka peridotite are PGE\|enriched, but otherwise possess residual characteristics arising from a minimum of 15% partial melting. It is suggested that mantle residuum by partial melting have low total PGE contents, fractionated chondrite\|normalized PGE patterns with negative or slightly flat slopes from Ir to Pd, and Pd/Ir<1. But, the total PGE contents, chondrite\|normalized PGE patterns and Pt/Ir, Pd/Rh and Pd/Pt values of the Dagzhuka peridotite are completely inconsistent with a residual origin. Partial melting would have partitioned all sulfide in the source into the melt. In fact, no sulfide or silicate melt remained in the Dagzhuka peridotite. Therefore, PGE in Dagzhuka peridotite are not present in sulfides. The PGE\|enrichment and fractionation of the Dagzhuka peridotites seem to arise from mantle metasomatism of melts/fluid enrich incompatible elements include Pt and Pt, but not from residual or percolation of sulfides. The enrichment of Cs, Rb, Ba, Th, U and LREE in Dagzhuka peridotite also give a hint of the mantle metasomatism. The abundance and distribution of PGE in the peridotite from the Dagzhuka ophiolite show the nature and evolution of the Dagzhuka upper mantle are distinctive.
文摘岩浆型Ni—Cu—PGE(platinum group elements,铂族元素)硫化物矿床是重要的铜镍矿床类型,探讨该类型矿床产出环境,成矿作用,矿床成因机制具有重要意义。本文通过对该类型矿床时空分布规律,矿床成矿过程,成矿理论,勘查技术等方面入手,搜集大量资料,综述该类型矿床在成岩成矿年代学、地球化学特征、矿床形态、成矿理论和成矿判别标志等方面的研究现状,结果表明:岩浆型Ni—Cu—PGE硫化物矿床在容矿岩石、成矿作用方式或主要金属组份、成矿构造环境等特点具有不同分类方式,并且硫化物(矿层)的分布都具有重力分异的特点;在时空分布规律方面国外Ni—Cu—PGE硫化物矿床主要形成时间是在中元古代以前,而中国主要形成时间是在中元古代以后;其中早古生代晚期(390~430 Ma)的该类矿床目前仅发现于中国,以夏日哈木超大型矿床为代表;成矿模式存在"岩浆通道成矿"和"小岩体成大矿"之争,二者在成矿位置、岩浆上侵方式、外来地壳硫的加入存在差异;依据全岩m/f与Mg~#比值判定岩体含矿性,结合铂族比值、磁铁矿的(Ni+Cr)/(Si+Mg)比值、磁铁矿Ti含量等可作为该类型矿床勘查评价的重要参考指标。
