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Sulphide occurrences in the
Rogaland Henrik Schiellerup, NTNU, Norway Work in progress The Rogaland anorthosite province in South Norway hosts a number of minor sulphide deposits as either disseminated, lumpy or semi-massive occurrences in anorthosite, or in one instance as a stratiform concentration in the Bjerkreim-Sokndal intrusion. Sulphide droplets are ubiquitous in all major mafic intrusions in Rogaland, which must have been formed from melts near-saturated in sulphur prior to emplacement. All sulphides are interpreted as being of magmatic origin and strictly comagmatic with their host intrusions. Both anorthosite- and norite-hosted sulphide deposits are characterised by restricted Re/Os, Pd/Cu and Cu/Ni ratios, which suggest that the sulphides exsolved from melts of comparable compositions. Low to sub-ppb level Pd and common-Os abundances for both anorthosite- and norite-hosted deposits imply that little interaction has occurred between immiscible sulphide and silicate melts. Although elevated R-factors are required to explain the composition of the stratiform deposit in the Bjerkreim-Sokndal intrusion, most anorthosite-hosted deposits are characterised by very low R-factors. The low R-factors in anorthosite-hosted deposits are in accordance with an origin by immiscibility in rather immobile intierstitial melts to the plagioclase crystal mush. Sulphide saturation therefore seems to be a late event in the history of massif-type anorthosite emplacement. We interpret the sulphide occurrences as resulting from differentiation of primary, relatively sulphur-rich magmas. References: Schiellerup, H., Lambert, D.D., Larsen, R.B., Nilsson, L.P., Duchesne, J.C., Robins, B. and Prestvik, T. (in prep.). Sulphide deposits related to the Proterozoic Rogaland anorthosite province, South Norway: Implications for sulphide ore genesis and massif-type anorthosite magmatism. |