Lateral variations in the platinum-group element content and mineralogy of the UG2 chromitite layer, Bushveld Complex
Lateral variations in the platinum-group element content and mineralogy of the UG2 chromitite layer, Bushveld Complex
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Bushveld 杂岩体 UG2 铬铁矿层铂族元素含量和矿物学的横向变化
DOI：
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发表时间：
1999
影响因子：
1.8
通讯作者：
R. Merkle
中科院分区：
文献类型：
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作者：
C. Penberthy;R. Merkle
对英国-马里卡纳地区若干UG2铬铁矿样品的调查揭示了显著的矿物学变化。大多数与典型UG2的偏差可归因于中低温下流体的相互作用，有时与局部扰动有关，如替换类伟晶岩、坑洞或断层的存在，而在其他情况下，则是由于不太明确的热液活动造成的。在某些地区，原生硅酸盐已被由石英、钠长石、榍石和含水硅酸盐（滑石、前褐长石、绿泥石、绿帘石和泵辉石）组成的低温组合所取代。在这些地区，贱金属硫化物组合由千粒矿+黄铁矿+黄铜矿组成，而不是在正常UG2中发现的五粒矿+黄铜矿+磁黄铁矿+或-黄铁矿组合。这种变化可归因于硫化物-铬铁矿平衡和与流体相互作用造成的铁和硫损失。在冷却过程中，铂族元素（PGE）从贱金属硫化物中排出，导致铂族矿物的存在，主要是铂族硫化物，被包裹在贱金属硫化物的颗粒边缘中或在边缘处。流体对硫化物的腐蚀导致这些铂族矿物在含水硅酸盐中的分离。在其他地方，与富铁交代流体的相互作用产生了铂族矿物组合，其特征是存在丰富的Pt-Fe合金、PGE硫砷化物、PGE碲化铋和其他非硫化物相。
Investigation of a number of samples of UG2 Chromitite from the Brits-Marikana area revealed significant mineralogical variations. Most of the deviations from typical UG2 can be attributed to interaction with fluids at intermediate to low temperatures, sometimes related to local disturbances such as the presence of replacement pegmatoid, potholes, or faulting, and in other cases resulting from less well-defined hydrothermal activity. In some areas, primary silicates have been replaced by low-temperature assemblages consisting of quartz, albite, sphene, and hydrous silicates (talc, prehnite, chlorite, epidote, and pumpellyite). In these areas, the base-metal sulphide assemblage consists of millerite+pyrite+chalcopyrite, instead of the pentlandite+chalcopyrite+pyrrhotite+ or -pyrite assemblage found in normal UG2. Such changes can be attributed to iron and sulphur loss resulting from sulphide-chromite equilibration and interaction with fluids. Expulsion of platinum-group elements (PGE) from base-metal sulphides during cooling resulted in the presence of platinum-group minerals, predominantly PGE-sulphides, enclosed in, or at the grain edges of, base-metal sulphides. Corrosion of sulphides by fluids leads to the isolation of these platinum-group minerals in hydrous silicates. Elsewhere, interaction with iron-rich metasomatic fluids resulted in a platinum-group mineral assemblage characterized by the presence of abundant Pt-Fe alloys, PGE sulpharsenides, PGE-bismuthtellurides, and other non-sulphide phases.