辉石巨晶中的硫化物及其成因

我国一些地区玄武岩辉石巨晶中的硫化物球泡(0.02-0.05mm)呈点阵式、散布式、定向带状或微裂隙羽状分布。硫化矿物组合是磁黄铁矿-镍黄铁矿-黄铜矿,其中以磁黄铁矿为主(～90％)。根据硫化物的规则排布以及高温矿物组合推测点阵式、散布式硫化物形成于地幔。是由溶解了～1％S的硅酸盐熔体在减压上升过程中析出过饱和的硫所致。

SULFIDES IN PYROXENE MEGACRYSTS AND THEIR ORIGIN

Four occurrences of sulfides have been recognized in pyroxene megacrysts:lattice-like, scattered, oriented belt and feather-like. The sulfide mineral association consists of pyrrhotite(90%), chalcopyrite(5%) and minor pentlandite. The first three types of sulfides are thought to have been formed in the mantle.At>20 kbar, silicate melt would contain 1-3% S. Once the drop of pressureoccurred, S solubility in the silicate melt would decreases, followed by themove-out of supersaturated S as immicible bubbles of sulfide. On the contrary,the fourth type of sulfides were produced by S-,C-rich volatile-fluid interaction. The results show that the geochemistry of sulfur in the mantle is complex,and the content of sulfur in a certain portion of basaltic magma may be higher.The soluble and then immiscible processes of sulfur in pyroxene megacrystsare an epitome of the formation of sulfide ore deposits related with basic andultrabasic magmas.