斑岩型铜矿床中铂族元素的研究现状与存在问题

Current situation and existing problems in the study of platinum group elements in porphyry copper deposits

铂族元素的研究在过去几十年取得了重要的进展。铂族元素可以赋存于不同的岩石类型中,形成于不同的时代。由于铂族元素具有特殊的化学性质,比较稳定且难熔于普通的酸、碱等,故铂族元素成矿具有特殊性。作为一种非常规铂族元素矿化类型,富铂族元素的斑岩型铜矿床的研究对研究铂族元素从地幔岩石圈转移进入花岗质岩石及随后从熔体进入流体并在硫化物中富集的机理,具有重要的研究意义。本文从斑岩型铜矿床中铂族元素的分布特征、矿化特征、铂族矿物特征、流体包裹体特征和富集成矿机理方面论述了斑岩型铜矿床中铂族元素的研究现状,并指出目前斑岩型铜矿床中铂族元素研究存在的主要问题,如影响斑岩型铜矿中铂族元素含量高低的影响因素不明确,富PGE斑岩型铜矿中流体包裹体研究不够系统,PGE的富集机理研究还欠深入,并指出今后我国斑岩型铜矿中PGE研究的重点,指出长江中下游地区一系列斑岩型铜矿床是我国斑岩铜矿中铂族元素研究的有利地区。

The study of platinum group elements has made important achievements in recent decades. PGE can be hosted in different types of rocks formed in different epochs. The ore-forming condition of PGE is also quite special due to their particular chemical characteristics such as stable chemical behaviors and refractory of common acid and alkali solutions. PGE mineralization in porphyry copper deposits belongs to one of the unconventional PGE mineralizations and is significant for the understanding of the problem how PGE were transported from lithosphere to granite and then concentrated in sulfides. This paper describes the current status of the study of PGE in porphyry copper deposits in the following five aspects： PGE distribution, PGE mineralization, platinum group minerals, fluid inclusions, and enrichment mechanism. The main existing problems in PGE study for porphyry copper deposits, such as unclear influencing factors on PGE distribution, inadequate systematic study of fluid inclusions, insufficient researches on the enrichment mechanism of PGE in porphyry copper deposits, are also discussed. The emphatic points in the study of PGE in porphyry copper deposits are pointed out, and it is further suggested that the series of porphyry copper deposits in the middle and lower Yangtze region are potential areas for the study of PGE in porphyry copper deposits in China. Mutschler et al. first described PGE content of Cordilleran alkaline suite porphyries containing copper and precious metals. Later, elevated PGE content was reported by Eliopoulos et al. based on a PGE content analysis of samples from different alteration zones. Then, much research work on PGE concentration in porphyry copper deposits has been done. A comparison of porphyry copper deposits in different tectonic environments made by Tarkian et al. shows that the porphyry Cu deposits of the island arc type have higher Pd and Pt content than those of the continental margin type. However, some other scientists hold that the PGE content is only related to the sulfide content of the porphyry Cu deposits and has no relation to the geological age, chemical composition of the intrusives and types of magma. So, what are the true factors which affect the PGE content in the porphyry copper deposits？ According to a careful optical and microanalysis, the presence of the platinum group minerals （PGM） has been revealed by some researchers. Most of the PGM so far diagnosed in the porphyry copper deposits are tellurides, arsenides, bismuthides and, especially, merenskyite. Based on fluid inclusion study, it is considered that the mineralizing fluids seem to be high temperature and high salinity fluids in the porphyry Cu deposits, and Pd and Pt might have been transported as chloride complexes under suitable physicochemical conditions.