A report on the geologic mapping of area C, Igayaza, Isingiro District, Western Uganda

Abstract

The geological mapping exercise was carried out in Gayaza, Isingiro district in western Uganda with the main objective of acquiring skills in geological mapping where acquisition, processing and interpretation of field data were the major steps undertaken. The mapping exercise lasted a period of 8 days. The methods used in acquiring data for the project involved; making groups of 6 students, standardizing pace lengths to measure size of large structures, establishment of stations on out crops, taking GPS readings and measurements of strikes and dips of structures in each of those established stations. After the field work, samples were sorted and taken to the laboratory for further analysis. The mapped area C is situated on the NE limb of the Gayaza synclinorium and is part of the Karagwe-Ankolean system which belongs to the Meso-Neo Proterozoic cover formations. It lies on a rugged topography with intervening valleys, steep gorges and rounded hills. The lithology of the area comprises of ridges that are predominated by quartzites on the peaks and thick argillaceous formations constituting shales (ferruginous & grey) and phyllitic shales along the slopes and in low lands. The rocks were deposited in the order of shales followed by sandstones that later metamorphosed to quartzites that occupy the top of ridges which were later intruded by granites. Long-term episodes of erosion and weathering of the granites formed arena structures which predominate much of the Karagwe-Ankolean system. Metamorphism of these rocks was mainly low-grade regional metamorphism evidenced by foliation and some index minerals such as chlorite. Sandstones and shales were metamorphosed to quartzites and phyllites respectively. The major structures in the area include: beddings, faults, folds and joints all exhibiting two major trends; NW-SE trend which is similar to that of the regional folds and NE-SW direction similar to that of the cross folds whereas the minor ones include: micro-folds, micro-faults, quartz veins, foliation, laminations and mud cracks. The drainage pattern of the area is essentially structurally controlled. It was concluded from the findings that the study area belongs to the lower part of the Karagwe-Ankolean system basing on the lithology, that is presence of thin quarzitic bands which are frequently boudinaged and sheared. 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.