四川力马河镁铁-超镁铁质岩体的地球化学特征及成岩成矿分析  

Geochemical characteristics and metallogenesis of the Limahe mafic-ultramafic intrusion,Sichuan.

作　　者：陶琰[1] 胡瑞忠[1] 漆亮[1] 罗泰义[1] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550002

出　　处：《岩石学报》2007年第11期2785-2800,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40573020;40673030);中国科学院重要方向项目(KZCX3-SW-125)资助。

摘　　要：四川会理力马河镍矿是峨眉山大火成岩省最重要的岩浆硫化物矿床之一,成矿岩体为一小型铗铁-超镁铁岩侵入体,由含斜长石的超镁铁岩(包括含长辉石橄榄岩和斜长橄榄辉石岩)和辉长岩类的镁铁质岩组成。矿床富含硫化物,成矿元素组合为铜、镍,铂族元素含量很低,没有铂族元素的工业富集,是峨眉山大火成岩省中富铜镍贫铂族元素的代表性岩浆硫化物矿床。本文对力马河镍矿成矿岩体的镁铁、超镁铁岩及矿床中各种硫化物矿石进行了主量元素、微量元素及铂族元素含量分析。分析结果表明,力马河岩体的镁铁、超镁铁岩属拉斑玄武岩成因系列,岩石特征微量元素比值大致与高钛的峨眉山玄武岩相当、与低钛的峨眉山玄武岩有明显区分,但估计原始岩浆强不相容微量元素绝对含量大大低于高钛玄武岩,因此,其成矿岩体不是与一般的低钛或高钛峨眉山玄武岩(不包括苦橄岩在内)直接对应的深成相。岩体超镁铁岩及矿石铂族元素组成特征表现为无钌亏损的型式,钯/铱比值较小、在5左右,也显著不同于一般的峨眉山玄武岩,而类似于峨眉山大火成岩省苦橄岩的铂族元素组成。运用岩石地球化学研究方法计算,原始岩浆为苦橄质成分:MgO含量约17%、SiO_2含量约48%。估计原始岩浆形成于130公里左右的深度,由类似于洋岛玄武岩岩浆源区成分的地幔经19%左右的部分熔融形成。超镁铁岩及硫化物矿石铂族元素含量一般在10^(-9)～10^(-8)级,铂族元素相对铜镍强烈亏损,铜/钯比值高于原始地幔10～100倍,铜镍铂族元素组成的原始地幔标准化曲线呈铂族元素显著亏损的"U"型。模式分析说明,导致铂族元素亏损的原因是岩浆成矿演化过程中多阶段硫化物熔离作用造成的,早期熔离出来的硫化物被丢失并造成岩浆中铂族元素亏损,其铂族元素亏损后的岩浆(第)二次硫化物熔离富�The Limahe nickel deposit is one of the most important magma sulfide deposits in the Emeishan LIP ( Large Igneous Province). The ore-bearing intrusion is a small mafic-ultramafic intrusive body which is fractionated well, consist of plag-bearing ultramafics and gabbros. The ores are rich in sulfide with high grade of nickel and copper but poor in PGE (platinum-group elements). It is a typical PGE-poor sulfide deposit in the Emeishan LIP. This paper will provide a basic study on major elements, trace elements and platinum-group elements for various rocks and ores in the intrusion. The major and trace elements variations of the rocks show tholeiitic evolution trend. The characteristics of the trace elements in ratio shows it is similar with high Ti Emeishan Continental Flood Basalt (ECFB), and different to Low-Ti ECFB. But the calculated concentration of strong incompatible trace elements in primary magma of the intrusion is much lower than High-Ti ECFB. So, the intrusion is not a differentiated body from a magma related with high-Ti or Low-Ti ECFB (not including picrites). The composition of PGE for the ultramafic rocks and sulfide ore are in a style of no Ru depletion, and the ratio of Pd/Ir is lower in about 5, that is quite different to ECFB, but same to the picrites in Emeishan LIP. By estmating, the composition of primary magma is picritic with about 17% in MgO and 48% in SiO2. The primary magma is originated from about 130 km depth in mantle, with degree of about 19% partial melting of the mantle which is analogous to the source mantle of OIB( Ocean Island Basalts). PGE analyses indicates that the sulfide ore are depleted in PGE with contents in pph to 0.1 X 10(-6). The ratio of Cu/Pd is higher over primitive mantle 10 to 100 times. Mantle-normalized Ni-PGE-Cu plots are distinguished in U shape. By model analyzing, it is concluded that the ores are formed by 'the second sulfide segregation'. The primary magma had sulfide segregation in the first, the removal of sulfide liquid from magma made the magma deplet

关 键 词：岩浆硫化物矿床 峨眉山大火成岩省 力马河镍矿 铂族元素 镁铁-超镁铁岩 

分 类 号：P588.125[天文地球—岩石学] P618.63[天文地球—地质学] P618.53