STUDY OF GEOLOGY, ALTERATION, AND MINERALIZATION IN LENANGGUAR AREA, SUMBAWA REGENCY, WEST NUSA TENGGARA

• Main Author: Rahmat Faizin, Lalu
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/65633
• Institution: Institut Teknologi Bandung

PT Amman Mineral Nusa Tenggara (PT AMNT) had numerous exploration area related to porphyry – epithermal deposit, including in Sumbawa. Blok Elang is a porphyry Cu-Au deposit located inside Wilayah Izin Usaha Pertambangan Khusus (WIUPK) owned by PT AMNT. Presently, further research is needed because there is an indication of mineralization around Blok Elang. Hence, research about geology, alteration and mineralization around Blok Elang porhyry Cu-Au on Lenangguar Area, Sumbawa, Nusa Tenggara is needed. The research covers around 1,2 x 1,9 km area, around 1 km to south from Blok Elang. Literatur review, geological mapping, petrographical analysis, mineragraphy analysis, and mineral spectroscopy analysis using Analytical Spectral Device (ASD) were done in this research. There are 16 thin-section, 6 polished section, and 280 mineral spectral graphic used in this research. The result of this research including, geological map and geological section, geomorphological map, alteration map and alteration section, and also paragenetic sequence of alteration and mineralization. All the data gathered and analyzed in order to understand the geology, alteration and mineralization of research area. There are three geomorphological unit named Heli Lava Dome, Lenangguar Fault Block Ridges, and Kuning Aluvial Plain. Geological unit of the research area, from the oldest to youngest were grouped into 5 unit, Andesite 1, Tuff – Lapili Tuff, Andesite 2, Breccia, and Aluvial Deposit. There are 3 stage of geological structure development of research area, phase 1 ( pre-porphyry intrusion development), phase 2 (relaxation of subduction cause porphyry intrusion), and phase 3 (post-porphyry intrusion development) There are 6 alteration zone and 3 alteration phase identified, Chlorite-Epidote–Calcite Zone on prograde phase, Chlorite-Sericite-Kaolinite zone on retrograde I phase, Sericite-Illite-Kaolinite±Chlorite zone on retrograde II phase, Sericite-Quartz±Chlorite zone on retrigrade II phase, Alunite – Pirophyllite-Illite-Diaspore-Quartz±Corundum zone on retrograde II phase, and Kaolinite-Dickite-Monmorillonite–Illite zone on retrograde II phase. Mineralization identified by texture, structure, and mineral assemblage of the mineralization, there are 5 distinct mineralization type named: [1] quartz-pyrite vein mineralization which related to D-type vein on porphyry deposit, [2] quartz-pyrite-galena vein mineralization which related to sub-epithermal vein, [3] argentit-galena-electrum-pyrolusite vein mineralization which related to intermediate sulphidation, [4] disseminated pyrite mineralization which enveloping porphyry deposit, and [5] oxidation and reduction mineralization which related to supergene processes.