The sulfides in the garnet pyroxenite xenoliths from Salt Lake Crater, Oahu |
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| Authors: | DE WAAL S A; CALK L C |
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| Institution: | 1National Institute for Metallurgy Johannesburg, South Africa
2U.S. Geological Survey Menlo Park, California |
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| Abstract: | Trace amounts of sulfide, ranging from 0?06 to 0?26 volume percent, are present in the garnet pyroxenite xenoliths in nephelinebasalt at Salt Lake Crater, Oahu, Hawaii. Microscopic studyrevealed the existence of three chemically and physically distinctsulfide types, i.e. enclosed, interstitial, and vein sulfides.The enclosed sulfide forms spherical inclusions in primary pyroxene,garnet, ilmenite, and spinel. It has a bi-modal chemical character,which may be in part due to alteration of some of the enclosedsulfide grains by the nepheline basalt host magma, but moreprobably represent Cu-Ni-rich sulfide liquid coexisting withCu-rich monosulfide solid solution. The interstitial sulfideis uni-modal and occurs in the interstices of the primary silicates.It has been subjected to intense chemical alteration by thenepheline basalt host magma. As a result the interstitial sulfidebecame Cu-poor with a varying Ni content, which indicates thatcomplete chemical equilibrium with the basalt host magma hasnot been attained. The vein sulfide, present as fracture fillings, is of late genesisand appears to represent partly altered enclosed sulfide. Thealteration process is the same as that which affected the interstitialsulfide. The mineralogy and chemistry of the enclosed sulfide suggeststhat the xenoliths have been abruptly cooled from about 1000?C, which represents the ejection of the xenoliths from thehost basalt magma. |
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