Pustaka Ilmiah Universitas Padjadjaran

Abstrak

Petrogenesis And Associated Hydrothermal Alteration Of Abangkomba Seamount, Flores Sea, East Nusa Tenggara

The Abangkomba seamount is located in the southernmost part of the “Neo-volcanic Komba-ridge” of submarine volcanic structures in the Flores Sea, East Nusa Tenggara. The collected dreged samples are dominated by igneous volcanic rocks, volcaniclastics, and pumice. The rocks vary from fresh to highly altered, the fresh are abundance in biotite and feldspar, and the latter are increasingly impregnated with sulfides, mostly pyrite.and rarely chalcopyrite and pyrrhotite. Chemical compositions indicating the samples are potassium-rich belong to shoshonite series. TAS diagram shows the samples mostly ranging between trachybasalt and trachyandesite, corresponding to increasing SiO2 and alkali contents. The Abangkomba seamount had undergone lower- grade differentiation with partial melting and associated with extensional structure. The altered samples of Abangkomba indicating three alteration zone, characterized by dominated alteration mineral: a) sub-prophylitic zone is marked by chlorite-carbonate-illite-pyrophyllite, b) phyllic zone is characterized by carbonate-sericite-illite, c) argillic zone consist of carbonate-smectite. Significant metals contents of Au-Ag and Cu-Zn shows from chemical analysis. Increasing of illite contents is corresponding to increasing in Au, this indicating that mineralization at Abangkomba is formed at near-neutral fluids environment, as also indicating by the occurrences of calcite minerals. The chemistry and mineralogy of altered rocks strongly resembles to the type of epithermal low sulfidation.