Abstract

Porphyry copper systems in Papua New Guinea and contiguous areas reveal distinctive intrusion geometries and fracture patterns. These distinctive characteristics are in turn related to their time of formation and to the tectonic province in which they occur.Porphyry systems of Miocene-Oligocene age occur in the mobile belt of Papua New Guinea, the Admiralty Islands, and on New Britain. In these older deposits, intrusion and fracture styles are indicative of porphyry bodies emplaced into settings produced and dominated by strike-slip stress regimes. The resulting geometrical distribution of fracture and intrusion patterns fixes the orientation of ambient principal stresses during their evolution. Derived principal stress directions appear to correlate with known and inferred directions and styles of coeval plate convergence.Younger porphyry systems of Pliocene and Pleistocene age occur on both mainland New Guinea and in some of the volcanic terrain of nearby islands. On mainland New Guinea, they occur scattered along the Aure tectonic zone some 250 km inland from the northern edge of New Guinea. In contrast with the older porphyry centers, the Plio-Pleistocene intrusion-fracture patterns are suggestive of forcefully emplaced porphyry intrusions into tectonically relaxed crustal blocks. Concomittant differential elevation of these young systems is an integral component of their tectonic evolution and is viewed as a consequence of high convergence rates between the Australian and Pacific Plates.

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