We investigated the duration of formation of the giant Ok Tedi porphyry copper-gold deposit in Papua New Guinea using zircon SHRIMP U-Pb dating. The intrusions that host the Cu-Au mineralisation have a maximum age of 1.43_x000D_
0.22 Ma. Since previously published K-Ar dates on the same intrusion constrain the last thermal event at 1.11_x000D_
0.05 Ma, we conclude that the magmatic-hydrothermal event that produced the deposit lasted ~0.45 million years (Myr). A comparison of Ok Tedi's calculated volatile fluxes with those from arc volcanoes and active mineralising hydrothermal systems suggests that the efficiency of metal deposition is a key factor in determining the duration of deposit formation._x000D_
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