The East Sunda Arc, Indonesia - an emerging world-class porphyry Cu-Au province

The East Sunda arc extends from western Java to Sumbawa in Indonesia and contains at least four world-class porphyry Cu-Au deposits (Batu Hijau, Elang, Tumpangpitu and Sori Onto), along with several porphyry and epithermal prospects. Late Miocene to Pliocene porphyry mineralization was associated with the emplacement of composite tonalite intrusive complexes emplaced into andesitic volcanic and volcaniclastic rocks. The geodynamic setting involved the subduction of the Roo Rise beneath the Sunda arc, with the porphyry deposits forming along the arc segment where the basement transitions from the Sundaland craton beneath eastern Java to oceanic crust beneath Sumbawa. The deposits have mineralized central domains associated with potassic alteration that has been extensively overprinted by intermediate argillic alteration (e.g., Batu Hijau and Elang), and/or advanced argillic alteration (e.g., Tumpangpitu and Sori Onto). High sulfidation epithermal gold mineralization has overprinted the Tumpangpitu porphyry in the Tujuh Bukit district, where an extensive lithocap is well-developed and has overprinted several porphyry deposits and prospects. Lithocaps also define the upper parts of Sori Onto and Elang, where they are superimposed over porphyry mineralization. Only the structural root zones of the Batu Hijau lithocap are preserved due to the greater degree of uplift and exhumation in SW Lombok.