Spatial and temporal constraints of leached Cu-Au porphyry shoulder high-sulfidation epithermal deposit: Insight from new discovered Kumbokarno Prospect, Trenggalek District, East Java

Abstract

We conduct microscopic and microprobe quantitative analyses to confine characteristics of the newly found Cu-Au high sulfidation deposit which interestingly seems to highly associate with the presence of iron oxide-hydroxide complex. The resulting paragenesis shows four generation phases, which are magmatic, deep hypogene, shallow hypogene, and supergene. The alteration pattern suggests presence of a concealed intrusion which ascends the hypogene mineralization forming-fluid. Quantitative microprobe analysis shows enrichment of copper and gold in various types of iron oxide-hydroxide texture. A unique repetitive pattern of high and low copper concentration is found overlaps with goethite-hematite band of colloform texture. An interesting pattern between gold and titanium is also found as gold is almost exclusively located inside or near Fe-rich leucoxene. We propose a model of leached Cu-Au porphyry shoulder high-sulfidation epithermal deposit system to explain the prevalent condition of Kumbokarno Prospect where intensive late oxidation acts as the main process of metal concentration.