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Abstract

The Island Copper Cluster (ICC), situated at the northern end of Vancouver Island, consists of five porphyry copper-gold-molybdenum systems genetically associated with stock and dike-like rhyodacitic porphyries of Jurassic age (approximately 180 ma) that intruded the island arc, calc-alkaline basalts, andesites and pyroclastic rocks of the comagmatic Bonanza Group. The systems (Island Copper; Bay Lake; G Zone; Red Island; and Rupert Inlet) are coincident with a series of northwest-trending magnetic highs and regional faults aligned for more than 10 km. They all share many similarities in the alteration-mineralization geometries but vary largely in size and grades. Copper-bearing skarn and vein-type mineralization also constitutes an integral part of the porphyry systems.

The only economic deposit of the cluster is the Island Copper mine controlled and operated by BHP Minerals Canada Ltd., which had initial estimated reserves of 257 million tonnes at 0.52 per cent copper and 0.017 per cent molybdenum at a 0.3 per cent copper cutoff grade. At Island Copper, mineralization is associated with multiphase rhyodacitic intrusions and hydrothermal breccia bodies. Available data suggest that the porphyry system evolved dynamically from an early, probably juvenile-dominated stage, to one strongly influenced by meteoric waters, as the main heat source cooled . and further intrusion and brecciation took place. Three main stages of alteration and mineralization have been differentiated:

An Early Stage, related to the intrusion of a main rhyodacite porphyry, involved the development of four outwardly progressing zones: a) a copper-barren stockworked core of quartz-amphibole-albite-magnetite( apatite, scapolite); b) a biotite-magnetite zone

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