摘要
利用锍镍试金富集-等离子体质谱（ICP—MS）测定法较系统分析了云南白马寨主要Cu—Ni硫化物矿石和主要围岩的PGE、Au、Cu和Ni含量，发现PGE含量均较低，其中块状硫化物矿石的∑PGE为78．2×10^-9～556×10^-9，橄榄辉石岩为0．472×10^-9～67．0×10^-9，辉长岩为0．847×10^-9，二辉岩为0．76×10^-9～0．809×10^-9．后期煌斑岩的PGE也很低（2．98×10^-9～4．07×10^-9）。各类矿石和围岩中∑PGE与Au，Ni与Cu之间呈明显的正相关关系。各类矿石的PGE原始地幔标准化曲线和Pt／Pd和Cu／Pd值与其各主要围岩非常相似，说明该矿Cu—Ni硫化物矿石为岩浆成因，且与围岩有成因上的联系。矿石和围岩较高的Pt／Pd值（平均0．83）显示其主要形成于单独的硫化物饱和事件，矿石中较高的Ir（0．77×10^-9～5．52×10^-9，平均2．35×10^-9）和Pd／Ir值（4．76-296，平均138）显示硫化物矿石可能受到后期强烈的热液蚀变。白马寨硫化物矿石较高的^187Os／^188Os初始值（0．456±0．026）显示地壳物质的加入是成矿的重要因素。计算显示该矿硫化物矿石中地壳来源Os超过30％。
Concentrations of platinum group elements （PGE）, Au, Cu and Ni in massive sulfide ores and related host rocks from Baimazhai Cu-Ni magmatic sulfide deposit were determined by using inductively coupled plasma mass spectrometry （ICP-MS） following nickel sulfide fire assay pre-concentration. The results show that the total PGE （∑PGE） are quite low, decreasing gradually from central massive ores （78.2× 10^-9-556 × 10^-9） to olivine pyroxenite （0. 472 × 10^-9 - 67.0 × 10^-9 ）, gabbro （0. 847 × 10^-9 ） and, websterite （0.76 × 10^-9 - 0. 809 × 10^-9 ）. The intruded lamprophyre dykes also show low ∑PGE （2.98× 10^-9 -4.07 × 10^-9）. The ∑PGE exhibits obvious positive correlations with Au, Ni and Cu contents. Primitive mantle normalized PGE patterns of the massive Cu-Ni ores are of the Pt-Pd type with relatively steep and trough-like patterns, which are similar to those of the host rocks. In addition, the Pt/Pd and Cu/Pd ratios of the massive sulfide ores are similar to those of host rocks. These characteristics suggest that sulfides in the massive ores are of magmatic origin, co-genetic with their host rocks. The relatively high Pt/Pd ratios of the Baimazhai massive sulfide ores （averaging 0.83） and their host rocks imply that the Baimazhai sulfides formed in a single sulfide saturation event. High Ir contents （0. 77 × 10^-9 - 5.52× 10^-9, averaging 2.35× 10^-9） and dramatically variable Pd/Ir ratios （4.76-296, averaging 138） of the massive sulfide ores suggest that the Baimazhai sulfide ores are of magmatic origin, but might have suffered significant late stage hydrothermal alteration. The initial ^187Os/^188 Os value of 0. 456±0. 026 indicates crustal contamination has played an important role during mineralization. The proportion of crust-derived Os is calculated to be more than 30%.
出处
《矿物岩石地球化学通报》
CAS
CSCD
2008年第3期239-246,共8页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
国家自然科学基金资助项目(40673045,40173025)
国家重点基础研究发展规划项目(2002CB412610)
南京大学内生成矿作用国家重点实验室开放基金资助项目
