Cu-Ni-PGE magmatic sulfide ores and their host layered gabbros in the Haymiliyah fossil magma chamber (Haylayn Block, Semail Ophiolite nappe, Oman)

Abstract

A disseminated sulfide-rich zone has been discovered in the gabbroic magma chamber. In this 150 m thick zone, thin, finegrained, concordant layers of noritic gabbro first appear in the layered gabbros, and contain most of the disseminated sulfides. Magmatic textures are well preserved. At the base of the section, the cumulates comprise olivine gabbros, gabbros and two-pyroxene gabbros. In the uppermost two-thirds of the sulfide-rich zone, two-pyroxene gabbros become predominant and grade locally into noritic gabbros and norites. This zone constitutes a transitional unit between an open-system fractionation represented by the main layered gabbro unit, and a closed-system fractionation corresponding to the planarlaminated noritic gabbros. Textural criteria evoke the segregation of an immiscible sulfide liquid which separated from a basaltic melt, prior to the first appearance of orthopyroxene as a main cumulus phase. Three sulfide associations were observed. -from Authors