铂族元素矿床的主要类型、成矿作用及研究展望

The major types,metallogenesis of platinum-group element deposits and some prospects.

铂族元素(PGE)矿床的研究在过去几十年取得了重要的进展。它可以赋存于不同的岩石类型、形成于不同的时代。内生 PGE 矿床与不同的岩浆类型及热液活动有关。由于铂族元素特殊的化学性质,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。PGE 矿床可划分为岩浆型、热液型、火山块状硫化物型(VMS)和外生型四大类型。岩浆型又可分为铜镍硫化物型、铬铁矿型和磁铁矿型,热液型主要有斑岩型和夕卡岩型,外生型包括黑色页岩型和砂铂矿型。本文讨论了各岩浆演化过程中:(i)硅酸盐和氧化物的分异,(ii)富 Fe 矿物(橄榄石、辉石、磁铁矿、铬铁矿)的分异,(iii)岩浆的混染,(iv)不同成分、硫不饱和的岩浆的混合等,都可以导致岩浆中硫达到饱和,一旦形成不混熔硫化物熔体,硫化物富集,将形成有经济价值的 PGE 矿床。同时,成矿还受温度、Ni 和 Cu 含量、体系中其它组分和硫逸度的控制。岩浆后期的热液蚀变会改变 PGE 的含量和品位,但典型的铂矿床一般没有遭受热液蚀变作用的显著影响。本文指出了铂族元素矿床研究存在的主要问题。如 PGE 矿床的物质来源、PGE 演化过程中的分配规律、铂族元素矿物(PGM)的赋存状态,并对以后的发展前景做了展望,指出西藏(蛇绿岩套铬铁矿亚类和俯冲增生弧斑岩型 Cu-Au 矿)和新疆(碰撞后二叠纪岩浆 Cu-Ni 硫化物型和黑色页岩型)是我国寻找 PGE 矿床的最有利地区。

The study of Platinum-Group Element （PGE） deposits has got important achievements in recent decades. PGE can be hosted in different type rocks, formed in different epochs, PGE deposits can be related to different types of magma and hydrothermal activities. The ore-forming condition of PGE is also special due to their particular chemical characteristics such as stable chemical behavior and refractory of common acid and alkali solutions. The paper suggested a systemic classification of four types and nine sub-types for PGE mineralization. Four major types of PGE deposit include magraatic type, hydrothermal type, volcanic massive sulfide （VMS） type and exogenous type. Magmatic-related PGE deposits can be further divided into Cu-Ni sulfide sub-type, chromite sub-type and magnetite sub-type. Hydrothermal-related PGE deposits contain porphyry Cu-Au sub-type and skarn Cu-Fe-Au sub-type. Exogenic- related PGE deposits can be divided into black shale-hosted PGE deposit and placer PGE deposit. And then we discussed the basic characteristics and enrichment regularity of all kinds of PGE deposits one by one. However, the genesis of PGE deposits is still in debate. Although there are several kinds of models, the saturation of S and fractionation of sulfide at the process of magma rising into the upper curst play an important role for PGE enrichment. With the evolution of magma, the following factors will eventually drive a sulfur-undersaturated magma to sulfur saturation： （i） fractionation of silicates and oxides; （ii） fractionation of Fe-rich minerals （notably olivine, pyroxene, chromite and magnetite） ; （iii） contamination of the magma; （iv） mixing of composition ally contrasting, sulfur undersaturated, magmas could trigger sulfur supersaturation. Once an immiscible sulfide melt has formed it needs to be concentrated so that the sulfides can be mined economically. Temperature, content of metal （ Ni and Cu ）, other components in the system and fs2 also the factors controlled the ore formation. Primary magraatic PGE mineralization show a low-temperature hydrothermal overprint, but relatively few cases have so far been documented where hydrothermal processes are the only or main factors responsible for PGE concentration. At last, the paper discussed the main problems for PGE study, such as origin and ore-forming conditions for PGE, partition regularity of PGE during the evolution of magma, the occurrence of platinum-group minerals （PGM） in the deposits and suggested some potential orientations, and further suggested that Tibet （ophiolite chromite sub-type and subduction-accretion arc porphyry Cu-Au sub-type） and Xinjiang （postcollisional Permian mafic-ultramafic Cu-Ni sulfide sub-type and black shale sub-type） are the most potential areas for PGE exploration in China.