Abstract

The Sally Malay nickel-copper sulfide deposit lies at the base of a small layered intrusion enclosed within granulite facies garnet-cordierite paramigmatites and mafic granulites. Evidence from phase changes at the migmatite contact, together with two-pyroxene thermometry on the mafics and ultramafics, indicates that emplacement of the intrusives postdated peak metamorphic conditions.The norites which host most of the mineralization are interpreted as a chilled border zone to the intrusion, into which settled an early separated sulfide liquid. Both sulfide-silicate textures and an indicated homogeneity of original sulfide compositions are in keeping with sulfide formation and emplacement as an immiscible liquid. Changes in magma composition associated with widespread salic contamination are evident in the border zone and, on a larger scale, may well have been the main factor inducing sulfide separation. This argument is supported by the close association of alkali silicate and sulfide, which suggests that alkalis were dissolved in the sulfide liquid and therefore participated in solubility equilibria.Excepting the effects of local deformation and the low temperature exsolution history indicated for the sulfides, the characteristics of the main mineralized zone are consistent with a little modified igneous origin. A subsidiary shoot which extends off-contact into the migmatites appears to represent fault-remobilized sulfides.

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