The geochemical role of primary copper-sulphur mineralization in the crystallization of the Freetown (Sierra Leone) layered gabbro

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Abstract
Summary: The separation of iron-titanium oxide droplets and the formation of olivine, in the Freetown layered gabbro, depleted the magma in iron and enriched the magma in copper. In magma injections in which the sulphur fugacity was sufficiently high, this resulted in the separation of immiscible copper sulphide droplets closely associated with the iron-titanium oxide droplets, and both were subsequently enclosed by olivine. A lower sulphur fugacity in other injections of magma suppressed the separation of the copper, which later appeared as native copper associated with euhedral titanomagnetite, and was enclosed by feldspar. Crystallization of the iron-titanium oxide droplets and subsolidus diffusion has resulted in granular exsolution of ilmenite from the droplets and lamellar exsolution of ilmenite in the euhedral titanomagnetite.