云南金宝山铂钯矿床铂族元素地球化学及找矿意义

Platinum group elements geochemistry of Jinbaoshan Pt-Pd deposit in Yunnan Province and its exploration implications

金宝山是中国目前发现的最大的独立铂钯矿床,该岩体基性程度高,主要由橄榄石、单斜辉石组成,含大量铬铁矿〔w(Cr)约为0.5%〕。铂钯矿石呈稀疏浸染状,硫化物含量少,高铂族元素、低铜镍含量。矿体与超基性围岩界线不明显,且二者具有相似的微量、稀土元素参数和微量、稀土、铂族元素标准化配分模式,表明两者的原始岩浆具有相似的性质。超基性围岩具有高的Pd/Ir、Ni/Cu比值和Pb负异常,相反,铂钯矿石显示为低的Pd/Ir、Ni/Cu比值和Pb正异常,两者具有相似的Cu/Pd、Cu/Pt比值(≤原始地幔值),表明铂钯矿石形成于地幔柱S低度饱和环境,超基性围岩可能形成于S饱和/不饱和的地球化学界面。铂族元素地球化学的差异表明含少量富铂族元素的硫化物的含矿岩浆可能注入于稍前侵入的、且未完全固结的超基性围岩中,形成似层状矿体。峨眉地幔柱早期硫低度饱和、融离出少量硫化物以及铂族元素在硫化物/硅酸盐相中极高的分配系数是导致金宝山矿石富铂钯、贫铜镍的根本原因。金宝山是极少有的全岩体Cu/Pd、Cu/Pt值均小于原始地幔值的矿床,表明该岩体的岩浆经历了硫化物富集铂族元素的过程,推测靠近峨眉地幔柱喷发中心的基性-超基性岩体是寻找铂族元素矿床最佳远景区之一。

Jinbaoshan which contains large amounts of chromites and has high Cr content （about 0.5 % ） is the largest independent Pt-Pd deposit which consists mainly of olivine and clinopyroxenite. Ores are sparsely disseminated and have a small amount of PGEenriched sulfides. The ores and ultrabasic wall rocks have similar trace elements, REE and PGE parameters and similar primitive mantle normalized patterns, implying that their parent magmas were alike. Samples from Jinbaoshan rock body have similar Cu/Pd and Cu/Pt ratios （4 the value of primitive mantle）. The ultrabasic wall rocks have high Pd/Ir and Ni/Cu ratios and Pb negative anomalies; on the contrary, the Pt-Pd ores have low Pd/Ir and Ni/Cu ratios as well as Pb positive anomalies. These data show that the parent magma of the ores had low S saturation, whereas the parent magma of the ultrabasic wall rocks was probably formed on the geochemical interface of S saturation related to Emeishan mantle plume. Ore mag- mas containing a little PGE-enriched sulfides were probably injected into the unconsolidated ultrbasic rocks which had intruded earlier, forming the quasi-bedded ore body. The low S saturation of Emeishan mantle plume in the early stage and high partition coefficient of PGE in the sulfide/silicate phases seem to be the essential factors responsible for high PGE and low Ni-Cu content of the Jinbaoshan deposit. Jinbaoshan is one of the rarely found rock bodies which have lower C2a/Pd and Cu/Pt ratios than the value of primitive mantle in China, implying that the rnagma of Jinbaoshan has experienced a procedure of PGE enrichment eruption center of Emeishan basalt seems to be one of The basic-ultrabasic intrusive body located close to the the best hopeful areas in search for PGE deposits.