A proton- and electron-microprobe study of gallium, nickel and zinc distribution in chromian spinel☆

摘要: Abstract Chromian spinels from a number of localities were analyzed by proton and electron microprobes to examine the variation trace elements in different geological environments. studied include those representing ophiolitic complexes, layered intrusions continental areas, Alaskan-type komatiitic subvolcanic sills, Ni sulfide ores metamorphosed mafic ultramafic rocks. Nickel concentrations range 30 4690 ppm (proton microprobe), with mean value 943 ppm. Nickel, favouring octahedral sites spinel structure, displays an overall increase decrease Cr/(Cr + Al Fe 3+ ) ratio. partitioning between chromian mantle silicates appears be primarily dependent upon major element composition spinel. Zinc 230 9810 cluster around 500 Ophiolitic display lowest Zn values. levels appear discriminate chromitite samples occurring as accessory dunites or other rock types. that are enclosed adjacent grains higher Zn. Zinc, strongly tetrahedral sites, crude negative correlation Mg/(Mg 2+ ratio vary function temperature. All contain measurable quantities Ga microprobe, ranging 10 208 There is reciprocal relationship concentration +Al positive concentrations. Measured whole supportive experimental mineral-melt partition coefficient Malvin Drake (1987). Similar peridotite xenoliths, mid-ocean ridge basalts oceanic-island basalts, correlates well 2 O 3 case most complexes. The seem have crystallized melts whose compositions similar partial upper mantle.