Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania
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- 作者：David M. Evans ; Leopold Byemelwa ; Jon Gilligan
- 关键词：Landmines ; Mineral exploration industry ; Metal detection
- 刊名：Journal of African Earth Sciences
- 出版年：1999
- 出版时间：August 1999
- 年：1999
- 卷：29
- 期：2
- 页码：329-351
- 全文大小：2916 K
文摘
Magmatic Ni---Cu sulphide deposits are often geometrically and compositionally complex, and it is important to understand this complexity at an early stage of their economic evaluation. The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20 % in 100 % sulphide. Generally, the lowermost layers have higher metal tenors, higher Ni/Cu, and lower S/Se ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt (R factor). Later sulphides separated from a more fractionated silicate melt with a lower R factor, implying an increasing contribution of sedimentary sulphide by wall rock assimilation during fractionation in a lower magma chamber.