Abstract

• The Soripesa prospect area is located at Maria village, Wawo district, Bima region in the eastern part of Sumbawa Island, Indonesia. This area is related with Cenozoic Calc-alkaline volcanic inner Banda-Sunda Arc. There have five main polymetallic epithermal quartz veins in the Soripesa prospect area, namely, Rini vein, Jambu air vein, Dollah vein, Merpati vein, and Arif vein. The dominant lithology is a lithic-crystal tuff of andesitic and dacitic composition and bedded limestone. Elemental compositions of sphalerites were analysed using Scanning Electron Microscope with energy-dispersive X-ray (SEM-EDX) method to identify their environment of ore deposition. Detected elements in sphalerite are Zn (63.48 wt.%), S (33.3 wt.%), Fe (1.04 wt.%), Ga (0.7 wt.%), Ge (0.54 wt.%), Cd (0.7 wt.%), and Ag (0.2 wt.%). Au content is below detection limit in all sphalerite. Ga/Ge ratios of sphalerites geothermometry indicate that the formation temperatures of sphalerite are between 180°C and 240°C. Based on the Fe mole %, sulfur activity ( ) is a little higher and between 10-10 – 10-11. Sphalerite are found in pyritic ore fields and low temperature condition. Sulfur activity and formation temperature plots show that ore-forming processes are formed under intermediate sulphidation state of epithermal system.