Abstract

The ages of several intrusive bodies associated with porphyry copper mineralization in the Star Mountains area have been further investigated. These intrusions are largely intermediate in composition and they cut through a Cretaceous to Upper Tertiary folded sedimentary sequence. The K-Ar results demonstrate that the majority of intrusions were emplaced between 7 m.y. and 1 m.y. ago. Discordant ages found within some intrusive bodies suggest that such bodies are in fact multiple intrusions of more than one age. New age data from the monzonites and diorites in the vicinity of the Mount Fubilan (Ok Tedi) porphyry copper deposit show a time gap of 1.5 m.y. between initial magmatic emplacement (2.6 m.y.) and subsequent copper mineralization (1.1 m.y.) associated with the Fubilan porphyries. Comparison of the ages of mineralized porphyries in the Star Mountains Intrusives (3.4 to 4.6 m.y.) and Antares Monzonite (2.4 to 3.1 m.y.) with older Miocene to early Pliocene ages determined on unmineralized parts of the same intrusions likewise indicates a distinct time interval between initial postemplacement cooling and the later hydrothermal alteration/mineralization processes.The youthfulness of intrusive igneous activity in this part of Papua New Guinea and Irian Jaya raises the possibility that the Quaternary stratovolcanoes in nearby areas of the Highlands may belong to the same tectonic regime, and therefore may similarly be of some economic potential.

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