A report on IGAYAZA (ISINGIRO) mapping project
Omuse, Joel Benjamin
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This write up contains the information obtained from the mapping exercise (project) which was carried out in Igayaza area, Isingiro district in Southwestern Uganda. The project was aimed at equipping geology students with field geologic mapping skills, data collection, processing and dissemination. The entire exercise involved collection of field data, data processing of the collected data and reporting of four main areas; stratigraphy, structures, petrography and metamorphism and regional synthesis. The area is generally characterized by a hilly topography with intervening narrow and broad low-lying areas which could have evolved due to differential weathering. It is also characterized by parallel and dendritic drainage and savannah vegetation. Settlement in the area is generally linear. Relief in the area is generally high making it generally difficult to access. Land use is dominantly agriculture and quarrying stone for construction material. Stratigraphy: Argillaceous and arenaceous rocks (shales, phyllites and quartzites) are characteristic of the area except for parts of granitic intrusions (arenas). As such, the area is placed in the middle part of the Karagwe-Ankolean system. Alternating conditions of low and high energy deposition are suggested for the deposition of the sediments in a possibly intercontinental basin of the Precambrian times (conditions). Structures: The major geologic structures encountered in the area are bedding and joints/fractures. Faults, folds, boudins, lamination are taken as minor structures. In the entire area, Beds dip to the SE and NW with low dips at the axis of the Gayaza syncline and steeply away from the axis of the syncline. In area L the preferred orientation of the beds is 0640, 36SE. The joints show two preferred trends in the NW-SE and NE-SW in the entire area corresponding to the regional and cross fold trends of the area and moderate to steeply dipping. These trends in area L are 3200, 54NE and 2280, 83.90NW. Folding is earlier than faulting and other structures in the area. Petrography and metamorphism: Petrographic results for area L reveal the area to be underlain by quartzites, siliceous, ferruginous and somewhat micaceous-shales. However, phyllites, conglomerates and phyllititic shales are found in other areas. The type of metamorphism in the area is generally regional (due to burial) of low to very low grade. Dynamic metamorphism in fault zones and metasomatism in areas near the granitic intrusions are also evident. Metamorphism increases in grade towards the base of the unit and with increasing proximity to the areas of granitic intrusion (arena). Lastly and conclusively, the area is part of the Karagwe-Ankolean system which is part of the Kibaran belt as seen from what has already been given and from the granitic intrusions and the tin mineralization areas visited during the field excursion part of the mapping project.