攀西裂谷地区层状镁铁岩的PGE矿化作用

PGE mineralization of layered intrusions in Panxi rift region,China

攀西裂谷位于四川西部，裂谷经历了元古宙和海西期二次地幔柱活动，形成多处穹窿构造和层状镁铁质岩体的侵入。后一期的层状岩体赋存著名的超大型钒钛磁铁矿床。中国和南非合作研究认为，层状岩体PGE矿化应进一步研究。以新街岩体为代表．经钻探工程建立了岩体剖面；岩石学、矿物学和地球化学研究证实，岩体有三个岩浆旋回和许多韵律层，层厚仅2～3cm。自上而下岩相为辉长岩、橄辉岩、辉石岩和橄榄岩，造岩矿物为贵橄榄石、普通辉石、钛普通辉石和中长石。岩体下部旋回，硫化物较富集，多在高镁质岩相。硅酸盐、氧化物和硫化物三系列矿物共生而不混熔。硫化物呈浸染状，主要有三层，产在橄榄岩、辉石岩和下辉长岩内。铂族矿物有砷铂矿、自然铂、硫锇矿、铋碲钯矿、碲铋矿、碲银矿、自然银等。PGE富集可能有三个阶段：岩浆早期，岩浆中“S”不饱和，PGE易进入硅酸盐；岩浆晚期“S”逸度增高，硫化物富集，为PGE富集阶段；热液阶段PGE再分配畜集。PGE和Ni、Cu、S为正相关关系，和Fe、Ti相辅相成，无明显关系。岩石中PGE背景值为（0．166～0．411）×10^-6，PGE矿化体的品位变化较大，为（0．94～0．976）×10^-6有的钻孔样品Pt＋Pd含量大于1×10^-6．可做进一步找矿的依据。

The Panxi rift is located in west Sichuan. The rift experienced the Paleozoic and Hercynian mantle plume activities and has a few dome structures and layered-intrusions; the intrusions host the well-known super large V-Ti magnetite deposits. The collaborated study by China and South Africa shows that the further study of the layered-intrusion PGE mineralization is needed. For instance, the section of Xinjie intrusion has been set up by drilling. The petrologic, mineral and geochemical studies show that there are three magmatic intrusion cycles and many cyelothems with two to three centimeter thickness. From top downwards, the intrusion is composed of gabbro, olivine gabbro, pyroxenite and peridotite. The rock-forming minerals include chrysolite, pyroxene, Ti-pyroxene and pseudoalbite. Sulfides are enriched in Mg-high rocks at the lower cycle. Silicates, oxides and sulfides co-exist unmixed. The sulfides are disseminated and mainly constitute three layers which exist separately within peridotite, pyroxenite and lower gabbro. The PGE minerals include sperrylite, native platinum, osmium-sulfide, tellurbismuth-palladium, botesite, tellurbismuth, native silver, etc. The PGE are enriched in three stages. At the early magmatic stage, the sulfur is unsaturated in magma and the PGE enter into the silicates; at the late magmatic stage, the sulfur fugacity increases and the sulfides are enriched leading to the enrichment of the PGE; at the hydrothermal stage, the PGE are redistributed. The PGE are positively correlated to Ni, Cu and S, and are supplemented with Fe and Ti but without close relationship in contents. The PGE contents of the rocks are high, ranging from 0. 166× 10^-6 to 0. 411×10^-6. The PGE contents of the PGE mineralized bodies are varied, ranging from 0. 94 × 10^-6 to 0. 976× 10^-6. The Pt＋Pd contents of some drill cores are higher than 1 × 10^-6 , which can be taken as a basis for further prospecting.