HR: 15:20h
AN: V33F-07    [Abstracts]
TI: Ancient crust in the world's youngest giant porphyry Cu-Au deposit, Ok Tedi, Papua New Guinea
AU: * van Dongen, M
EM: michiel.vandongen@sci.monash.edu.au
AF: Autralian Crustal Research Centre, School of Geosciences, Monash University, PO Box 28E, Clayton, VIC 3800, Australia
AU: Weinberg, R
EM: roberto.weinberg@sci.monash.edu.au
AF: Autralian Crustal Research Centre, School of Geosciences, Monash University, PO Box 28E, Clayton, VIC 3800, Australia
AU: Tomkins, A
EM: andy.tomkins@sci.monash.edu.au
AF: Autralian Crustal Research Centre, School of Geosciences, Monash University, PO Box 28E, Clayton, VIC 3800, Australia
AU: Armstrong, R
EM: richard.armstrong@anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Building 61, Mills Road, Canberra, ACT 0200, Australia
AB: The Ok Tedi Intrusive Complex in Papua New Guinea is dominantly composed of shoshonitic monzonite to monzodiorite. It is associated with one of the world's largest Au-rich porphyry Cu deposits (PCDs). The first zircon U-Pb zircon crystallization age determination for the Ok Tedi intrusions obtained using SHRIMP analysis are presented here. The mean concordant age of the mineralized monzonite porphyry is 1.12 plusminus 0.05 Ma, making Ok Tedi the world's youngest giant PCD and implying that it was exhumed at a rate of 3-5 km/Myr. This is consistent with Pliocene exhumation rates for Papua New Guinea. Many of the analyzed zircon grains contained inherited Proterozoic cores (ranging ~1.7-2.1 Ga, ²⁰⁶Pb/²⁰⁷Pb age), suggesting that magma evolution involved assimilation and/or partial melting of an ancient fragment of the North Australian Craton, possibly in the lower crust. Recycling of older cratonic continental crust has also been documented for the giant deposits of Bingham (USA) and Chuquicamata (Chile), suggesting that crustal contamination is a common process in the genesis of magma that forms PCDs, either by assimilation or by mixing of lower-to-middle crustal material with hydrous mantle derived melts. It is discussed whether this should be considered vital for the genesis of this deposit type.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1115 Radioisotope geochronology
DE: 3618 Magma chamber processes (1036)
DE: 3619 Magma genesis and partial melting (1037)
DE: 3665 Mineral occurrences and deposits
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting