[H-RE13] 資源地質学

[HRE13-P03] Geology, mineralization and carbonate-rich potassic alteration at the Humpa Leu East porphyry Cu-Au prospect, Hu'u district, Sumbawa Island, Indonesia

*Fadlin Fadlin^1,2、Ryohei Takahashi¹、Andrea Agangi¹、Pearlyn Manalo¹、Hinako Sato¹、Arifudin Idrus³、Bronto Sutopo⁴、Rachmat Pratiwinda⁵ (1.Akita University、2.Study Program of Geological Engineering, Jenderal Soedirman University (Indonesia)、3.Department of Geological Engineering, Universitas Gadjah Mada (Indonesia)、4.PT. Antam, Tbk (Indonesia)、5.PT. Sumbawa Timur Mining (Indonesia))

キーワード：HLE porphyry Cu-Au, mineralization, carbonate-rich potassic alteration, Sumbawa Island, Indonesia

The Humpa Leu East (HLE) prospect is one of the newly discovered porphyry Cu-Au prospects in the Hu'u district, Sumbawa Island, Indonesia. The deposit formed in an active continental margin with a calc-alkaline magma affinity. The HLE porphyry Cu-Au prospect is characterized by typical multiphase porphyry intrusion associated with hypogene mineralization. It is hosted by andesitic and crystalline tuff, volcanic breccia, andesite lava and diorite intrusions. The causative intrusions include diorite and diorite quartz. Five hydrothermal alteration types are identified at the surface: potassic, propylitic, advanced argillic, intermediate argillic, and argillic. The presence of a carbonate-rich potassic alteration in this deposit, indicative of CO₂-rich fluids, is uncommon in porphyry Cu-Au systems. This study revealed that the mineralization stages of the HLE can be divided into early, intermediate, and late stages. The early-stage is associated with M (magnetite ± bornite ± chalcopyrite), A (quartz + magnetite), and AB (quartz + magnetite + chalcopyrite ± pyrite) veins. These veins mainly formed in the potassic alteration zone. The intermediate stage is characterized by B (quartz + chalcopyrite+ pyrite) and C (chalcopyrite ± pyrite) veins, which mostly occur in the chlorite-sericite and sericite zones. The late stage is mostly associated with D (calcite + gypsum + quartz + pyrite ± chalcopyrite ± sphalerite ± galena) veins with a sericite-chlorite halo. Two styles of mineralization have been identified in the HLE prospect: quartz-sulfide veins and disseminated sulfides. Petrography and electron microprobe analysis identified that the carbonate replaced Ca-rich plagioclase in potassic alteration zone. Fluid inclusion petrography and Raman spectroscopy confirmed the presence of monophase vapor inclusions in quartz containing CO₂ and CO₃. Biphase (V+L) and multiphase (V+L+S) fluid inclusions in quartz also contain CO₂ in the vapor phase. We consider that the carbonate was mainly formed by the reaction between Ca²⁺ from Ca-rich plagioclase and CO₂-rich magmatic fluids.