ALTERATION, MINERALIZATION, AND CHARAKTERISTICS OF HYDROTHERMAL FLUID RELATED WITH EPITHERMAL GOLD DEPOSIT AT TUJUH BUKIT OPEN PIT MINE, BANYUWANGI DISTRICT, EAST JAVA

• Main Author: Abiyya Khayusty, Afif
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/45453
• Institution: Institut Teknologi Bandung

The Tujuh Bukit gold mine is an ancient volcano Late Miocene-Pliocene aged on the Java Southern Mountain. It is located in Pesanggaran subdistrict, Banyuwangi, East Java. The research is based on detailed mapping methods on the open pit wall bench of Pit A, Pit B-East and Pit B-West supported by petrographic data, atomic absorption spectroscopy (AAS), mineragraphy and fluid inclusion. The Tujuh Bukit epithermal gold deposits are formed in volcanoes environment associated with phreatic and phreatomagmatic eruption processes. The volcanoes contains of Pyroclastic Flow Breccia, Maar Diatreme (Phreatic Breccia 1, Phreatic Breccia 2, Phreatomagmatic Breccia, Sedimentary Maar, and Phreatic Breccia 3) and Pyroclastic Fall Tuf. One of phreatic and phreatomagmatic eruption products is the Phreatomagmatic Breccia Unit, located at Pit A with matrix supported and the fragment contained diorite clast with wispy texture as juvenile clast, identified as the proximal zone (root zone) of the diatreme. The Maar Sediment Unit have been found at Pit B-West contains of mudstone and siltstone intercalation, the estimated thickness is 10 meters and exposed at the top of the maar diatreme. The alteration zone was controled by lithology and main geological structure. High grade mineralization is generally associated with hydrothermal breccia lithology and strike-slip fault structure relatively NNW-SSE orientation. The study area consists of four alteration zones, there are Vuggy / Massive Silica Alteration Zone, Silica ± Alunit ± Dickite Alteration Zone, Dickite ± Kaolinite ± Silica Alteration Zone, and Kaolinite ± Illite Alteration Zone. Hydrothermal fluid charakteristics of epithermal gold deposit in Tujuh Bukit based on microthermometric calculation data, the average value of Tm = -2.8 ° C to -1.3 ° C, Th = 151 ° C to 309 ° C, and salinity value 2.16 to 4.52 wt% NaCl equivalent, with indication of boiling phase in low salinity conditions.