Preliminary Study on Surface Geology and Hydrothermal Alteration of Ambado_PK20 Prospect Zone, Djibouti
ASMA Abdi, SACHIHIRO Taguchi, THOMAS Tindell
Djibouti is among the few countries that import a bigger percentage of its electrical power. Currently Djibouti is putting efforts on developing indigenous sources of power such as geothermal and solar energy to meet the current demand as well as reduce over-reliance on importion of power. Ambado_PK20 is one of the promising geothermal fields in Djibouti.This study used the ability of remote sensing technology to identify and to map the fault and alteration zones in a Ambado_PK20 geothermal prospect area by using ASTER L1T data source. Though Ambado_PK20 geothermal field lacks active fumaroles and rock alterations are not visible on the surface, some water wells located in this zone have temperatures between 40°C and 73.6°C. Due to the presence of this ground thermal anomaly, Ambado_PK20 geothermal field was identified for geothermal exploration. Structurally, the study area is mainly affected by a network of normal faults that are N80°-N110°, ie EW, which are parallel and synchronized by the rifting of the Tadjoura gulf. The latter are intersected by a minority of the faults which are N20°-N70° directions, ie NS. The movements resulted by these fault networks are believed to have a direct impact on thermal anomaly occurrences in the area. The first objective of this study was to identify the fault and to assess whether there is any relationship between faults and the occurrence of thermal anomaly in the area. The second was to map the distribution of the alteration mineral assemblages, and veriﬁed by laboratory analysis (Petrography and X-Ray Diffraction analysis). The fault map showed that areas with a high number of faults were also associated with thermal anomaly occurrences. The alteration map identified clay mineral and iron oxyhydroxide (e.g. hematite, geothite) of hydrothermal origin. Resultats of the alteration map from the aerial image are consistent with mineralogical data obtained from XRD and petrographic studies of the sample taken closely neighbor the anomaly zone. These alteration minerals can be attributed to hydrothermal fluid flowing upward under high water-rock ratio, through highly permeable rocks and controlled by geological structures in the study area. The results of this study showed that the Ambado_PK20 geothermal field has intermediate seated reservoir with temperatures in the range of 100 -130°C. This energy can be converted to electricity via binary power plants and the exhausted brine be used for direct use.
|        Topic: Geology||Paper Number: 12026|