滇西菲红超基性岩风化壳铂族元素地球化学行为

GEOCHEMISTRY OF PLATINUM GROUP ELEMENTS IN REGOLITH FROM THE FEIHONG ULTRAMAFIC COMPLEX,WESTERN YUNNAN

近年来在世界不同地区进行了风化过程中铂族元素的地球化学行为研究。作为中国西南部的第一个实例 ,本文研究了云南西部菲红超基性岩体上发育的红土化风化剖面。矿物学和微量元素地球化学研究证明该风化壳是超基性岩风化的结果。文中详细讨论了风化壳的地质、矿物学、红土化和铂族元素地球化学特征。结果表明 ,风化壳的红土化程度不高 ,仍处于红色粘土阶段 ;风化壳上部的表层土壤带和铁质粘土带中铂族元素总量至少富集了 3.5 7～ 7.87倍 ,其中Ru和Pd的富集程度较大 ,Ir的富集程度中等 ,Pt和Rh的富集程度较小 ,使得铂族元素的配分模式由基岩的Pt富集型转变为风化壳的Ru Pt富集型 。

The geochemical behaviors of platinum group elements (PGE) in weathering processes have been studied in different parts of the world in recent years. As a first example in southwestern China,here an investigation is made in a lateritized regolith profile,which is developed over the bedrock of the Feihong ultramafic complex in western Yunnan,and proved to be the weathering profile of ultramafic rock by research results from mineralogy and trace elements geochemistry. The characteristics of filed,mineralogy,lateritization and geochemistry of the PGE in the regolith are discussed in detail. The results show that the lateritization degree of the regolith is not high,yet in the red clay stage,which has a mineral assemblage with the co existence of different types of clay minerals such as 2∶1 type of chlorite,montmorillonite and illite and 1∶1 type of kaolinite. The PGE contents in the top soil and ferruginous clay zones of the regolith increase with a total enrichment of 3.57 to 7.87 as compared with the bedrock. The fractionation of PGE is developed during lateritization as implied by the changes of relative distribution and C1 chondrite normalized models of PGE from Pt concentration type in the bedrock to Ru Pt concentration type in the regolith. The enrichment degrees of Ru and Pd are relatively high,and Ir is moderate,while Pt and Rh are low.