| Abstract |
Aluto Langano geothermal field is one of geothermally active area located in Aluto volcanic complex (AVC). To study the subsurface geology and mineralogy of wells LA-9D and LA-10D, various analyses have been conducted including: binocular microscope analysis, petrography microscope analysis, X-ray diffractometer analysis and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) analysis. Lithologies that are found in the study wells, identified with the aid of binocular microscopy and petrographic microscopy, are pyroclastics, silicic tuff and breccia, sediments, rhyolite, trachyte, basalt and ignimbrite, while ICP-OES analyses also led to the identification of very scarce and thin layers of trachyandesite, basaltic trachyandesite, trachydacite, basaltic andesite and andesite units. Hydrothermal alteration minerals are found as replacement of primary minerals and as fillings of veins and vesicles. Four alteration zones are recognized in both study wells, and include an unaltered zone, smectite zone, illite/chlorite zone and illite/chlorite/epidote zone. Eight feed zones (with one major and seven minor) were identified in well LA-9D and seven (one major with six minor) feed zones in LA-10D are observed. Most of the feed zones are located in fractured basaltic units. The highest temperature recorded was more than 300°C in well LA-9D below 1560m depth, and below 1600m in LA-10D, the recorded temperature indicated more than 300°C. Both wells appear to be in the upflow zone of the system. |