Sub-surface geology, hydrothermal alteration and 3D modeling of wells

Aluto Langano geothermal field is located in the Aluto Volcanic Complex (AVC), within the Central Main Ethiopian Rift System (CMERS). AVC is a silicic peralkaline complex, which is affected by Wonji Fault Belt (WFB), trending NNE-SSW. Ten exploratory wells (LA-1 to LA-10D) have been drilled in Aluto Langano geothermal field, with a maximum depth of 2500m and maximum measured temperature of 335°C. This study focused on sub-surface geology and hydrothermal alteration of wells LA-9D and LA-10D. The wells were drilled directionally on the top of AVC. Data form neighboring wells (wells LA-3 to LA-8) are used for comparison purposes. 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.