Timing of sulphide saturation and ore formation in the Sudbury Igneous Complex

Abstract

The Sudbury Igneous Complex (SIC) is widely believed to be the result of melt generation due to meteorite impact, and so models of Ni-Cu-PGE sulphide ore formation must be reconciled with this hypothesis. Moreover, the formation of the Ni and Cu sulphide ores is a product of sulphide saturation and segregation of immiscible sulphide melts, and like the ores at Noril’sk, those at Sudbury leave a fingerprint of the process in the comagmatic silicate rocks which are bereft of much of their Ni, Cu and PGE. At Sudbury, the thickest part of metal-depleted norite is located proximal to the largest known deposits, viz. the Creighton, Copper Cliff and Frood-Stobie Deposits. It is believed that the formation of the initial immiscible sulphide took place shortly after melt sheet formation, but well before any significant amount of silicate crystallization; sulphide saturation and segregation from the crustal melt sheet likely occurred under superheated conditions. The geological data provide important constraints on the sequence of events that formed the different orebodies in contact, footwall and offset dyke environments.