A Geologic mapping Report of Area I, Igayaza, Isingiro district in South Western Uganda.

Abstract

The geological mapping of Igayaza village was from 1st to 10th March 2021 where we travelled to Isingiro district in western Uganda. The major aim of this field mapping was to train students to obtain hands-on experience in field geological mapping activities from field preparations to geological written report and practically learn field geological mapping and field data collection techniques and procedure. The methods used after field trip include laboratory petrographic analysis and interpretation using a microscope, structural data analysis and interpretation using stereonet software and use of ARCGIS to digitize and draw cross sections from the map.

This looks at the study of the general geology, stratigraphy, structure, petrography and metamorphism of the KA system in southwestern Uganda as the northern extension of the kibaran mobile belt.

Isingiro area is relatively low to medium in elevation. Most of the areas in Isingiro district Uganda covered by the conspicuous Karagwe-Ankolean system which is part of the Kibaran belt of Central Africa system of rocks on which the geologic mapping exercise was done. The mapped area (Area I) lies between UTM coordinates of Eastings (250000-252000) and Northings (9915000-9917000) in Nyakigyera sub county, Isingiro district. It borders Igaharo to the East and Kabingo to the South, and covers a total land area of four-square kilometers.

The area is underlain by rocks of Paleoproterozoic age that include granites, quartzites, shales, conglomerates and phyllites. In general, this Isingiro region and surrounding area areas belong to paleoproterozoic geology of Uganda under Rwenzori fold belt and this is where we find karagwe-Ankolean system of rocks in Uganda. The major structures encountered in this area includes joints, bedding planes, faults, folds and minor structures are quartz veins, crenulation cleavage. The Gayaza Synclinorium is a typical example of a cross fold with the axis plunging to the southwest at a small angle within the Karagwe-Ankolean rocks of SW Uganda. The fold is about 6km across and is preserved as a topographic high towering over the adjacent low-lying anticlines. The major structural trends are attributed to both Regional and Cross-folding oriented in the NW-SE and NE-SW directions.

The petrographic analysis of the thin sections indicates that most common minerals in the rocks are quartz, clay minerals and iron oxides. The metamorphism is largely regional metamorphism and generally of low grade. Contact metamorphism occurs in rocks adjacent to granitic intrusion. From rocks of very low grade in the synclinorium, a steep gradient is obvious towards large batholithic granites in the arena hence the metamorphism increases with stratigraphic depth and with proximity to the granite intrusions.