Abstract
Indonesia is a country that has several world-class copper-gold deposits, particularly in eastern Sunda arc. The Hu’u complex has several prospects in the surface as lithocap of extensive epithermal style alteration, but some were detected associated with porphyry beneath the surface. The study focuses on hydrothermal breccia cement as a factor influencing the porphyry system in the Hu’u district. The methods used is mineralogical analysis with petrography and μ-XRF elemental mapping on hydrothermal breccia samples. The Hu’u district is interpreted as a paleo-volcano; a member of the Old Volcanics Rocks Formation. The Humpa Leu East lithology consists of pre-volcanics unit (lava and pyroclastics), diorite, andesite-μ-diorite, and tonalitic intrusion at the depth. Hydrothermal alteration evolved from tonalite body to outward, consist of potassic, inner propyllitic and overprinted by phyllic and advanced argillic. Several phases of hydrothermal activities occur in this system, including the hydrothermal breccia phase associated with complex fluids. The hydrothermal cement of Humpa Leu East porphyry at least have three phases of mineralogical assemblages and possibly influencing the mineralization. The mineralogical assemblage of hydrothermal cement in HLE consists of quartz-feldspar-plagioclase-biotite as a high-temperature phase; then followed by epidote-sericite-chlorites-anhydrite-carbonates in medium temperature; there are aluminum-rich clay minerals interpreted as gibbsite. Mineralization occurs in three phases including chalcopyrite-magnetite, bornite-chalcopyrite and chalcopyrite-sphalerite phases. The occurrences of chalcopyrite at all phases indicate the stability of intermediate sulfidation proses in Humpa Leu and as a possible factor to answer the abundant copper in the Hu’u hydrothermal fluid system
Highlights
Indonesia is a country that has several world-class copper-gold deposits such as Batu Hijau, Martabe, Grasberg - Ertsberg, and the discovery of Onto CopperGold Deposits in Hu’u Complex in 2013 [1]
The deposits classify as world-class with more than > 5 million ounces gold equivalent, which is dominantly associated with porphyry-epithermal type
Hu’u complex has several prospects in the surface as low to medium metal’s grade lithocap of large epithermal style alteration, but some were detected associated with porphyry beneath the surface
Summary
Indonesia is a country that has several world-class copper-gold deposits such as Batu Hijau, Martabe, Grasberg - Ertsberg, and the discovery of Onto CopperGold Deposits in Hu’u Complex in 2013 [1]. The latest research in Hu’u complex was done by Burrows et al (2020) and reporting that the U-Pb zircon age for the andesite that caps the volcano-sedimentary 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. The latest research in Hu’u complex was done by Burrows et al (2020) and reporting that the U-Pb zircon age for the andesite that caps the volcano-sedimentary 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 The mineralization in this ‘young’ ages to be interested in exploration, and the character of deposits in Hu’u still open up opportunities for new discovery in this belt or Pleistocene ages volcanism or magmatism. In hydrothermal breccia cement using μ-XRF, which aims to determine the character and paragenesis of hydrothermal system in HLE
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