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Petrography and electron microprobe analysis were used to investigate the mineralogy, bulk composition, abundance, and distribution of Cu-Fe-Ni sulfide phases in a suite of about 25 alkalic-basalt-hosted xenoliths from Kilbourne Hole, New Mexico. The xenoliths include spinel lherzolites, spinel clinopyroxenites, clinopyroxene megacrysts, mafic granuloblastites, and a sillimanite-quartz granuloblastite. Sulfide abundance is low in all the xenoliths, but shows a maximum (∼0.5 vol. %) in pyroxenites and megacrysts. The sulfides occur as interstitial to silicate and oxide grains, fully enclosed and isolated in grains, and along fracture surfaces in grains. The major sulfide phase is monosulfide solid solution (∼pyrrhotite), accompanied by variable amounts of pentlandite, and cubanite. Both the mineralogy and bulk sulfide composition are distinguishable among the xenolith types: Ni-rich for the lherzolites, Ni-poor for the crustal xenoliths, and intermediate for the pyroxenites, megacrysts, and composite xenoliths. The sulfides in the Kilbourne Hole spinel lherzolites most likely result from partial retention, in the residual silicate rock, of an immiscible sulfide formed during mantle partial melting.

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