超基性岩红土风化壳中铂族元素(PGE)的地球化学特征及其表生行为:来自印尼与中国不同气候环境红土剖面的对比研究  

Geochemical behavior of Platinum Group Elements(PGE)during the laterization process of the ultramafic rock:A comparative study of two laterite profiles under different climate conditions from Indonesia and China

作　　者：付伟[1,2] 黄小荣[2] 杨梦力[2] 张亚倩[2] 牛虎杰[3] 

机构地区：[1]桂林理工大学隐伏金属矿产勘查广西重点实验室,广西桂林541004 [2]桂林理工大学地球科学学院,广西桂林541004 [3]金川集团股份有限公司,甘肃金昌737100

出　　处：《地学前缘》2015年第2期160-173,共14页Earth Science Frontiers

基　　金：国家自然科学青年基金项目(41102051);广西自然科学基金项目(2012GXNSFAA053187;桂科青0991083);广西重点实验室建设项目(11-031-20;12-071-20);桂林理工大学"八桂学者"项目

摘　　要：选择印度尼西亚苏拉威西岛Kolonodale地区和中国云南省元江地区的两处红土剖面为研究对象,对比研究不同气候环境下PGE在超基性岩红土风化壳中的地球化学特征及其表生行为。测试数据表明,PGE在两例红土剖面中都表现出了不同程度的表生富集效应,相对于基岩的最大富集系数分别达5.42(Kolonodale剖面)和6.52(元江剖面),并且PGE在风化产物中的富集系数与样品的红土化强弱指标(S/SAF值)关系密切。但PGE在两例剖面中的垂向分布特征明显不同,它们的含量曲线分别呈"哑铃状"(Kolonodale剖面)和"倒勺子状"(元江剖面)。地球化学证据指示,风化壳中的PGE主要源自基岩中的铬铁矿,它在超基性岩红土化过程中的表生行为与Fe和Cr等元素高度一致,显示出残余富集的习性。这种机制导致了PGE富集段出现在元江和Kolonodale风化壳剖面的上部(红土层)。此外,气候环境通过制约基岩的红土化程度来对PGE的表生行为产生影响。Kolonodale剖面的红土化程度高于元江剖面,PGE在强烈红土化作用下会在风化壳内部发生迁移再分配,这是导致在Kolonodale剖面的腐岩层中也出现PGE富集现象的可能机制。研究进一步证实,Pd和Os在红土化程度较高的风化壳中活动迁移性较强,它们会与Pt、Ir、Ru和Rh等元素发生相对明显的内部分异。除此之外,在超基性岩红土化过程中IPGE与PPGE之间或PGE内部各单项元素之间的内部分异现象并不显著。To study the geochemical characteristics and evolution of PGE during the laterization of the ultramafic rock, the Kolonodale profile from Indonesia and Yuanjiang profile from China were selected as the comparative studying targets. Our work revealed that the PGE supergene enrichment are apparent in both two laterite profiles, and the enrichment factors relative to parent rocks are 5. 42 （Kolonodale profile） and 6. 52 （Yuanjiang profile） individually. This PGE enrichment effect is closely associated with the laterization degree of the weathering product. However, the vertical distribution pattern of PGE is different in these two cases, showing ＂dumb bell＂-like shape in the Kolonodale profile and ＂inverted spoon＂-like shape in the Yuanjiang profile. Geochemical evidence indicated that chromite minerals are the original source of PGE in the laterite crust, and the geochemical behavior of PGE is highly consistent with Fe and Cr, which show typical residual concentration during the laterization process. This mechanism led to PGE enrichment in the upper part of the laterite crust. Furthermore, climate constrained the laterization degree of the ultramafic rock, and then influenced the concentration and behavior of PGE during weathering. For the Kolonodale profile, PGE may have undergone more migration and redistribution in the laterite crust due to the higher laterization degree, leading to one more PGE concentration segment occurring in the lower part of the laterite crust. Our work further confirmed that Pd and Os are more mobile in the intensively weathered crust, and they may show relatively high differentiation with Pt, Ir, Ru and Rh. Except this, the internal differentiation of PGE was not significant in general during the ultramafic rock laterization.

关 键 词：铂族元素 地球化学行为 红土风化壳 超基性岩 气候背景 

分 类 号：P618.53[天文地球—矿床学] P595[天文地球—地质学]