The Onto Cu-Au Discovery, Eastern Sumbawa, Indonesia: A Large, Middle Pleistocene Lithocap-Hosted High-Sulfidation Covellite-Pyrite Porphyry Deposit

The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 +/- 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 +/- 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 +/- 0.02 and 0.35 +/- 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 +/- 0.22 to 0.284 +/- 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 +/- 0.064 to 0.038 +/- 0.018 Ma. The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 +/- 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 +/- 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 +/- 0.02 and 0.35 +/- 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 +/- 0.22 to 0.284 +/- 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 +/- 0.064 to 0.038 +/- 0.018 Ma. The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 +/- 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 +/- 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 +/- 0.02 and 0.35 +/- 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 +/- 0.22 to 0.284 +/- 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 +/- 0.064 to 0.038 +/- 0.018 Ma. The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 +/- 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 +/- 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 +/- 0.02 and 0.35 +/- 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 +/- 0.22 to 0.284 +/- 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 +/- 0.064 to 0.038 +/- 0.018 Ma. The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 +/- 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 +/- 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 +/- 0.02 and 0.35 +/- 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 +/- 0.22 to 0.284 +/- 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 +/- 0.064 to 0.038 +/- 0.018 Ma. The Onto system is exceptionally young and formed rapidly in the middle Pleistocene and is not significantly eroded. A U-Pb zircon age for the andesite that caps the volcanosedimentary host rocks provides a maximum age of 0.838 +/- 0.039 Ma, with a slightly younger porphyry zircon crystallization age of 0.688 +/- 0.053 Ma. Re-Os dating of molybdenite that is associated with both the quartz vein stockwork and high-sulfidation assemblage copper mineralization shows overlap between 0.44 +/- 0.02 and 0.35 +/- 0.0011 Ma. 40Ar/39Ar ages for alunite within the advanced argillic alteration block ranges from 0.98 +/- 0.22 to 0.284 +/- 0.080 Ma, and alunite closely associated with covellite spans a period from 0.537 +/- 0.064 to 0.038 +/- 0.018 Ma.