【摘要】 金宝山和白马寨铜镍硫化物矿床均主要赋存在峨眉山大火山岩省中,但其矿化特征存在许多不同。本文着重对比了金宝山铂钯矿床和白马寨铜镍矿床的铂族元素(PGE)地球化学特征,发现前者表现为高ΣPGE及低的(Cu+Ni)、Pd/Ir(3.84~26.49)、Cu/Pd(46.91~1309.58)值和Au/Pd值,相反,后者表现为低ΣPGE、高(Cu+Ni)、Pd/Ir(4.72~297.2)、Cu/Pd(10875.13~974788.55)值和较高的Au/Pd值。金宝山和白马寨PGE原始地幔标准化配分模式均主要表现为左倾型,但二者表现为镜像关系。金宝山较白马寨的PGE间相关性好,可能说明白马寨母岩浆经历了较为复杂的地质过程,其铂族元素体系因此受到较大的扰动。结合前人有关杨柳坪铜镍铂族元素矿床的铂族元素数据,认为峨眉地幔柱形成铜镍铂族元素矿床大致可以分成3个阶段:1金宝山阶段:即为S的低度饱和阶段,为峨嵋地幔柱上升初期,吸收少量壳源物质,由于PGE在硫化物中很高的分配系数,导致少量硫化物熔体从硅酸盐中萃取大量PGE和少量Cu-Ni熔离出来,与铬铁矿、橄榄石和辉石等,于高温下结晶分异堆积而成金宝山岩体,形成独立铂钯矿床。金宝山岩体为富含PGE硫化物熔体的主要接受者;2杨柳坪阶段:即S的中度饱和阶段,为峨嵋地幔柱上升的中期,吸收较多的壳源物质,发生较强的硫化物熔离作用,较多的Cu、Ni和PGE随硫化物熔体向下运移堆积而成杨柳坪铜镍铂族元素矿床,杨柳坪岩体为富含铂族元素硫化物熔体的次要接受者;3白马寨阶段:即S的高度饱和阶段,为峨眉地幔柱上升的后期,由于吸收大量的壳源物质,自身温度降低,发生强烈的硫化物熔离作用,大量铜镍及少量残余在硅酸盐中的PGE随硫化物熔体熔离出来堆积而成。由于PGE数量稀少,达不到工业品味,因此只能形成独立的铜镍矿床,白马寨母岩浆为铂族元素的给予者。更多还原

【Abstract】 The Jinbaoshan and Baimazhai ore deposits are two magmatic sulfide deposits hosted in the Emeishan large igneous provinces. In this paper, platinum group elements (PGE) geochemistry of the two deposits were compared, and the results show that the Jinbaoshan is characterized by high total PGE (ΣPGE), low (Cu+Ni), Pd/Ir (3.84~26.49), Cu/Pd (46.91~1309.58) and Au/Pd ratios. On the contrary, the Baimazhai is characterized by low ΣPGE, high (Cu+Ni), Pd/Ir (4.72~297.2), Cu/Pd (10875.13~974788.55) and Au/Pd ratios. The two deposits have enantiomorphous primitive mantle normalized PGE patterns. The Jinbaoshan mine has more obvious positive correlation among PGE elements and Cu, Ni than the Baimazhai, probably implying that the PGE compositions in the Baimazhai intrusive was disturbed as its parent magma had experienced more complicated evolutional processes than the Jinbaoshan. Based on analytical data of this study and Yangliuping Cu-Ni-PGE deposit, the Cu-Ni-PGE ore formation processes of the Emei mantle plume are divided into three stages: 1) the Jinbaoshan stage, namely low S-saturation stage, during which the Emei mantle plume was mixed with a little crust material and just changed into S-saturated from unsaturated at the beginning of ascending, that a little sulfide melt segregated from silicate. Because of high patition coefficient of PGE between sulfide and silicate melt, a little sulfide melt can scavenge a large number of PGE from silicate melt. Consequently, the Jinbaoshan independent Pt-Pd deposit was formed by cumulation of a little PGE-enriched sulfide and the co-crystallizing olivine, pyroxene, chromite, etc. at high temprature; 2) the Yangliuping stage, or moderate S-saturated stage, during which the continuously ascending Emei mantle plume absorbed more crustal material and became moderately S-saturated and resulted in more PGE, Cu and Ni segretated from the silicate. More PGE, Cu and Ni accumulated and formed the Yangliuping deposit. 3) the Baimazhai stage, or high S-saturated stage, within which the terminal Emei mantle plume absorbed a lot of crustal material and became highly S-saturated, resulting in strong sulfide segregation. Cu, Ni and PGE in the silicate segregated with sulfide melt and formed independent Cu-Ni deposit.更多还原