福建牛头山新近纪碱性玄武岩中地幔岩包体内硫化物研究

福建牛头山一带新近纪碱性玄武岩中含有尖晶石二辉橄榄岩包体。这些地幔岩包体内普遍存在有硫化物。硫化物按产状和成因分为两类:1)分布于寄主矿物内部,未与裂隙相连,是地幔岩浆作用的产物;2)分布于颗粒内或颗粒边部,在裂隙上或与裂隙相连,是地幔流体交代作用的产物。电子探针分析表明,15个硫化物测点中,除2个黄铜矿、1个硫铜铁矿外,其余为不同Ni/Fe(mol比)比值的铁镍硫化物:6个测点为富镍镍黄铁矿,其Ni/Fe=0.98～2.79,(Fe+Ni)/S=1.03～1.08;2个为针镍矿,其Ni/Fe=5.5,(Fe+Ni)/S=1.01;4个测点为富镍磁黄铁矿,其Ni/Fe=0.29～0.49,(Fe+Ni)/S=0.79～0.94。4粒单一硫化物矿物的成份是不均一的,多数表现为自中心到边部Ni含量和Ni/Fe值呈增加趋势,而Fe和Cu含量呈减少趋势。本研究还发现单一硫化物中由中心到边部金与镍大致有相同的变化趋势。

SULFIDES IN MANTLE-DERIVED XENOLITHS FROM NEOGENE ALKALI BASALTS AT NIUTOUSHAN, FUJIAN

The mantle-derived spinel lherzolites captured in the alkali basalts in age of Neogene occurred in the Niutoushan district, Fujian province, China. The isolated sulfides were commonly found in minerals of the mantle-derived xenoliths. They could be identified into two types. One was sulfide inclusion occurring in host minerals, which produced during gradually cooling of sulfide-silicate melt. Another was sulfide phase distributing in intergranular or the fissures, related to mantle metasomatism. Fifteen points of sulfides were analyzed by electron microprobe. Except two chalcopyrites and one talnakhite, six of those were pentlandites, with Ni/Fe ( molar ratio) ranging from 0.98 to 2.79 and (Fe+Ni)/S ( molar ratio) ranging from 1.03 to 1.08; four pyhrrotites, with Ni/Fe ( molar ratio) ranging from 0.29 to 0.49 and (Fe+Ni)/S ( molar ratio) ranging from 0.79 to 0.94, and two millerites, whose Ni/Fe ( molar ratio) equalled to 5.5 and (Fe+Ni)/S ( molar ratio) equalled to 1.01. The composition of a single sulfide was not homogeneous, mostly with Ni contents and Ni/Fe (molar ratio) increasing from the center to the margin, while Fe and Cu contents decreasing from the center to the margin. The changing tendency of Au was similar to Ni, namely, increasing from the center to the margin in a singlr sulfide.