GEOLOGICAL SUBSURFACE ON GEOTHERMAL SYSTEM OF CANGGA-PUMA BASED ON WELL 84 AND 95, DOMPU DISTRICT, SUMBAWA ISLAND, WEST NUSA TENGGARA

• Main Author: Arif Ganianda, Fary
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69713
• Institution: Institut Teknologi Bandung

Cangga-Puma geothermal system located in Hu’u Sub-District, Dompu district, West Nusa Tenggara is generally composed of Tertiary volcanic rocks located in East Sunda Volcanic Arc. This study discusses geological conditions and hydrothermal alteration of correlation well 84 and 95 (owned by PT. Sumbawa Timur Mining). The data were used is rock samples from drill cores supported by secondary data in the form of LiDAR imagery, abundance of elements and oxides, and alteration minerals. Rock samples were analyzed megascopically and microscopically to identify lithology, alteration minerals, overprinting stages or paragenesis, temperature measurement, and fluid inclusions. Secondary data of alteration mineral from Analytical Spectral Devices (ASD) instrument was used to determine the assemblage of hydrothermal alteration mineral that are acidic or neutral, and the data abundance of elements and oxides from Inductively Coupled Plasma - Optical Emission Spectrometry (OES) were used to characterize specific alteration types and create subsurface zoning. The study area is located in the geomorphological unit of Pure Mountains and Pure Flow Ridge. The lithology of study area is composed of Andesite Lava from Pliocene to Pleistocene, also Diatreme Breccia, Crystal Tuff, Pure Andesite Flow 1 and 2 from Pleistocene. The study area consists of five hydrothermal alteration zones, namely epidote + chlorite + calcite zone, chlorite ± calcite ± anhydrite zone, silicic zone, quartz + kaolinite + dickite ± alunite ± pyrophyllite zone, and montmorillonite + kaolinite zone. The geological structure that was developed is the Danakakila normal-sinistral fault, which may be the path of hydrothermal fluid flow that controls the stage of alteration development. The recent temperature of well 84 at a depth of 912 m was recorded at 210?, which has decreased based on microthermometric calculations of fluid inclusions sample in quartz + calcite + zeolite veins with homogenisation temperature value of 229-288?, which is included in epidote + chlorite + calcite alteration stage with a temperature gradient range of 200- 320?.