Geological mapping project report of Area L, Igayaza-Isingiro District

Abstract

The Geological mapping exercise was carried out in Gayaza, Isingiro district, western Uganda for about 10 days, with the aim of acquainting us with skills in geological mapping. The mapped area is within the Karagwe-Ankolean system of rocks (ca. 1400-950 Ma), which is the northern most extension of the Kibaran mobile belt. The mapping exercise involved conduction of field work based on surface geological mapping in which the study area was traversed and a mapping plan developed and various observations on outcrops made were recorded. . After field work, samples were sorted and taken to the laboratory for further analysis and data acquired for structures was interpreted and analyzed. The findings were compiled with its interpretation made. In this report the a detailed geological study of area L in Gayaza is discussed, a chapter on regional synthesis is included to cover the whole of the Gayaza synclinorium in relation to the rest of the Karagwe-Ankole rocks. The lithology comprises of thin arenaceous formations that are predominated by quartzites while the thick argillaceous formations constitute of shales, phyllites and schists. The quartzites are mainly found at the ridge summits occasionally with semi-persistent conglomerates while the shales are found along the flanks of ridges and in valleys between ridges. This results in a region of rugged topography. The Gayaza synclinorium fold plunges in the Southwest, and is at least 6km across in the Karagwe-Ankolean rocks of SW Uganda. Area L is found in the synclinorium. The rocks were deposited in the order of shales followed by sandstones that later metamorphosed to quartzites that occupy the top of hills which were later intruded by granites and as a result of erosion and weathering the granites formed arena structures which predominate much of the Karagwe Ankolean system. The type of metamorphism that affected these rocks is mainly regional and of low grade evidenced by foliation and some index minerals such as chlorite. Sandstones and shales were metamorphosed to quartzites and phyllites respectively. Deep, quiet and shallow water dynamic environments of deposition were proposed due to the presence of shale and quartzites and some structures such as beds and laminations in shales. Folding is mainly of two major types i.e. regional folds whose fold axes trend in the NW-SE direction and the cross folds whose fold axes trend in the NE-SW direction. The structures that were found in the mapped area include joints, beddings, laminations, faults, rods, boundinge, crenulations, quartz veins; these were mapped at different scales. The economic potential of the area is low since no economic minerals have been discovered. However, some of the economic activities carried out include; farming, cattle keeping, quarrying and brick making.