云南省中西部红色风化壳中铂族元素分布特征

Geochemical Characters of Platinum Group Elements of the Regoliths in the Midwest of Yunnan Province

近年来,铂族元素以其广泛的地质活动环境受到越来越多的关注,人们对铂族元素的研究也从其在硫化物熔体、硅酸盐熔体和热液流体中的富集成矿行为逐渐延展到其在表生风化过程中的地球化学迁移行为。本文通过对我国云南省中西部潞西菲红、元谋朱布和弥渡金宝山3个具有铂族元素矿化的超基性岩体形成的红色风化壳研究发现,三地风化壳化学风化程度远不及世界上热带、亚热带地区的典型红土风化壳,但是其红土化程度存在依次降低的次序。分别对三地风化壳铂族元素分析表明,随着风化壳红土化程度的增高,铂族元素富集程度也在增高,并且不同铂族元素在同一风化壳的不同位置也具有不同富集程度,表明伴随着红土化过程,铂族元素在地表风化壳中发生了迁移富集和分异作用。研究发现,低价铁离子对铂族元素络合物的还原作用和高价铁氧化物对铂族元素的吸附作用都对铂族元素的重新分配并富集具有重要意义;6个铂族元素不同的地球化学行为导致了其在风化壳中的分异,其中,Rh在红土化过程中的行为和铂族元素整体行为体现出高度一致性,因此Rh可以作为表生作用过程中铂族元素的标型元素;Au和铂族元素在红色风化壳中的分布具有一定相似性,根据粘土型Au矿床的存在,推测也有红色粘土型铂族元素矿床的存在。

Platinum Group Elements（PGE）has been received increasing attention due to their extensive existence in various geological environments.Based on the investigation in three red regolith profiles which are developed over the bedrocks of ultrabasic complexes in Feihong,Zhubu and Jinbaoshan regions of midwestern Yunnan Province,it is found that the lateritization degree of the three regolith regions are far weaker than those of the typical regoliths in other places such as tropic and subtropic areas,and the intensity shows decreasing trend from Feihong,Zhubu and Jinbaoshan.PGE geochemical analysis shows that with increasing of lateritization,the concentration degree of the PGE is higher.And PGEs have different values at different positions even in the same regolith,indicating that PGEs migrated,enriched and differentiated in the regoliths in company with the process of lateritization.Our study found that Fe2＋ is of great importance to the reduction of PGE complex and that the sorption of Fe3＋ oxide to PGEs also has great impact on the redistribution and enrichment of PGEs.Different geochemical features of six elements in PGEs result in the differentiation in red regoliths,and Rh shows highly consistent with the overall performance of PGEs during the lateralization.Therefore,Rh can be used as typical element of PGEs in epigenesist.Au and PGEs have similar distribution characters in red regoliths,and based on the occurrence of red clay type Au deposit,it can be inferred that there must be some red clay PGE deposits in the world.