Mineralization in the Argentine Islands consists of sparse quartz-molybdenite-chalcopyrite and quartz-pyrite veinlets, and conspicuous quartz magnetite veins. It is associated with a Tertiary granodioritic pluton (cut by small irregular bodies of quartz monzonite) which intrudes mainly Mesozoic volcanic rocks. Hydrothermal alteration, affecting both the intrusion and the volcanic rocks, consists of a core of potassic enrichment which passes directly into a zone of propylitic alteration. Phyllic alteration is present but is restricted to small areas localized well within the zone of propylitization. The type of mineralization and distribution of alteration zones provides evidence of the nature of the root zone of a porphyry copper system.

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