四川丹巴杨柳坪铜镍铂族元素硫化物矿床成因初探

四川丹巴杨柳坪铜镍铂族元素硫化物矿床的含矿岩体围绕杨柳坪穹状构造分布,侵位于泥盆系大理岩、炭质板岩中.自下至上岩体由蛇纹岩相、滑石岩相、次闪石岩相和蚀变辉长岩相组成.似层状浸染状矿体分布于岩体底部蛇纹岩相内,透镜状块状矿体则分布于底部及底板围岩中,后者与前者在空间上有密切的依存关系.矿石中主要硫化物矿物为磁黄铁矿、镍黄铁矿和黄铜矿;块状矿石中还发现辉砷钴矿,以及砷铂矿、碲锑钯矿等铂族元素矿物.野外关系表明杨柳坪含矿镁铁-超镁铁岩体为火山通道相浅成岩体.含矿岩体和大石包玄武岩的地球化学特征表明两者为同源岩浆产物,与其它地区峨眉山玄武岩地球化学特点的相似性,表明它们也是峨眉地幔柱活动的产物.当玄武岩浆上升到浅成岩浆房中时,随着岩浆分离结晶作用的进行,硫化物从玄武岩浆中熔离出来并向下聚集是主要成矿作用.

Origin of Yangliuping Ni-Cu-PGE sulfide deposit in Danba, Sichuan

The mafic-ultramafic sills bearing the Yangliuping Ni-Cu (PGE) sulfide deposits are distributed in the Yangliuping tectonic dome. The sills intrude into the Devonian strata of marble and slate. The ore-bearing sills are composed of serpentinite, talc, tremolite, and meta-gabbro from bottom to top. The (layered) disseminated ore-bodies are situated in the serpentinite at the bottom of the sills, and the lenticular massive ore-bodies are located in the footwall marble or at the bottom of the sills below the disseminated ore-bodies. The primary sulfides in the ores include pyrrhotite, pentlandite, and cholcapyrite, and (colbaltite) and some platinum-group minerals including sperrylite and testibiopalladite occur in the massive ores. The geological relationship between the sills and the wall rocks indicate that the ore-hosting (intrusions) are sub-volcanic sills which act as feeders to the overlying basalt flows. The geochemical (characteristics) of the ore-hosting sills and the Dashibao basalt in the Yangliuping area indicate that they (originated) from the same parent magmas caused by the Emeishan mantle plume that produced the (Emeishan) flood basalts. When the magma emplaced in the sub-volcanic sills, the sulfides dissolved from the basaltic magma and was rich in Ni, Cu, and PGEs, as the basaltic magma became S-saturated because of the decreasing of the temperature and pressure and the introduction of amount of S from the wall rocks.