Geological field mapping report of Group J, Igayaza, Isingiro District, Western Uganda

Abstract

This report summarizes the findings made in the mapping project that was carried out in Gayaza area located in Isingiro district in south-western part of Uganda. Field studies and analyses involved mainly traversing the mapping areas while collecting geo-data, collecting samples at specified noted locations laboratory analysis, and data analysis. While traversing the survey areas, rock descriptions were noted along with measurements like strikes, dips, and rock trends in general. Several rock types were noted to occur in varying quantities and these included; shale, quartzite, granites, phyletic shales, laterites and conglomerates. Shales cover over 70% of the mapped area while quartzite though abundant occurs in lesser concentrations. The other rock types occur in very little quantities in a few areas. Petrographic analysis reveals that clay minerals are the most abundant in all shale types while quartz was most abundant in quartzite. Several geological structures were encountered in the mapped area most of which point to tectonic process of formation. Structures found include; folds, joints, beddings, foliation, mud cracks, boudinage and cleavages. Most major structures show a preferred orientation in the NW/SW and NW/NE trends as seen in beds and joints. These trends are attributed to pre-historic compressional forces that were oriented in directions NW-SE and NE-SW, forming structures oriented in NE-SW and NW-SE respectively. Several features including relict bedding in quartzites could be used to deduce that metamorphic grade was low to moderate grade on a regional scale. Metamorphic grade also decreases away from arenas which initially contained metamorphosing granite intrusions. Contact metamorphism was also noted in rocks just adjacent to granite intrusions. Microscopic analysis reveals wavy extinction in quartzite thin sections indicating deformation by metamorphism or tectonic stress. Micro fractures and boudinage in some areas indicate brittle deformation. The drainage pattern of the area is essentially structurally controlled. No economic minerals were found but some industrial minerals of high place value such as sand, kaolin, shales and quartzites mainly used for construction works do exist. The major economic activities in Gayaza area include: crop growing (especially matooke), animal keeping (on a small scale) and brick laying together with stone quarrying.