The geology of Uganda extends back to the Archean and Proterozoic eons of the Precambrian, and much of the country is underlain by gneiss, argillite and other metamorphic rocks that are sometimes over 2.5 billion years old.
Sedimentary rocks and new igneous and metamorphic units formed throughout the Proterozoic and the region was partially affected by the Pan-African orogeny and Snowball Earth events.
Through the Mesozoic and Cenozoic, ancient basement rock has weathered into water-bearing saprolite and the region has experienced periods of volcanism and rift valley formation.
The oldest rocks in Uganda date to the Archean and are more than 2.5 billion years old, forming a gneiss and granulite complex in the north and center of the country.
The slightly younger Karuma Complex dated to 2,990 million years ago is found in a tract of country extending north-east from the eastern shores of Lake Albert to the Victoria Nile.
[1] The Watian Group rocks in the West Nile region date to the Mesoarchean, 2.9 billion years ago and metamorphosed to granulite grade on the sequence of metamorphic facies.
The Buganda Group of rocks comprising orthoquartzites, conglomerates, metavolcanics, slates, phyllites, mica schists and metasandstones is found around the shores of Lake Victoria from Jinja westwards and across as far as the largely faulted eastern edge of the Western Rift.
[3] The Kibaran orogeny impacted the region in the Mesoproterozoic, forming the arenites, argillites, siltstones and metacalcareous rocks of Karagwe-Ankole Belt, which unconformably overlies the Buganda-Toro System in the southwest.
An arcuate suite of dykes were emplaced around 1,370 million years ago within the largely Neoarchaean and Palaeoproterozoic rocks from Kampala westwards.
[4] The Neoproterozoic Bunyoro Series a 160-kilometer section of central Uganda, built on a bottom unit of tillite, likely related to the Snowball Earth glacial deposits from the period.
The gneisses, granulite, marble, amphibolite and quartzite of the Karasuk Supergoup underlie the border region north of Nakapiripirit, extending east into Kenya.
[2]: 264 Structurally, the geology of Uganda is strongly influenced by fold belts and shear zones, as well as the East Africa Rift related crustal downwarping in the Pleistocene that formed Lake Victoria.
The country sits on two of the several fragments of African continental crust which have remained largely stable over this period of time; the Tanzania Craton in the south and the Bomu-Kibalian or Northeast Congo-Uganda Shield in the north.
[10] Gold has been mined from quartz vein and alluvial deposits near Busia, hosted in an Archean greenstone belt, and occurs in Paleoproterozoic and Mesoproterozoic metasediments at Buhweju and Kigezi.