Stretching northwest from Kakamega in Kenya into Uganda, the Busia-Kakamega Greenstone Belt is located on the northern shore of Lake Victoria. The belt is made up of a general series of sedimentary and volcanic rocks that face northeast and are punctuated by granitoids. According to Sharp et al. (2016), the oldest rocks are the pre-2750 Ma Samia Hills Group in the west, followed by the 2700–2670 Ma Ndori group and the 2670–2660 Ma Yala group, which extend eastward into the 2660 Ma Kavirondo group. The adakitic rocks in the Yala River group are intercalated with sandstone and conglomerate, which were previously part of the Kavirondo group. The volcanic units and their intrusive equivalents include rocks of komatiitic, tholeiitic, calcalkaline, and high potassium adakitic composition.

The Ndori Group hosts the komatiitic suite, which consists of ultramafic volcaniclastic rocks and high-Mg basalts. The granitoids can be divided into two groups: a younger, about 2650 Ma high potassium suite that postdates the Kavirondo group, and an older, calcic syn-volcanic suite that predates the deposition of the Kavirondo group sedimentary rocks. At the outcrop scale, the majority of the rocks in the Busia-Kakamega Greenstone Belt exhibit remarkably little strain. The presence of mafic volcanic meta-tectonites is an exception. A minimum date for this early deformation is provided by field relations, which indicate that the Assembo granitoid, which is around 2670 Ma, passively invades these meta-tectonites. In outcrops, the younger Kavirondo group’s rocks are locally bent and occasionally sliced by a sharp cleavage. A maximum age for this younger cleavage is given by the Kavirondo group’s inferred age of about 2660 Ma, which also makes it abundantly evident that the belt contains at least two distinct generations of structures. Several lines of evidence suggest east-northeast faults throughout the region. Discordant characteristics, these faults are probably indicative of younger deformation. The north-striking intrusive contacts of the Maragoli and Mumias external batholiths, which date to around 2655 Ma, truncate the northeastern major structural grain of rocks in the centre portion of the belt.

Two unofficial geological regions have been identified within the Busia Kakamega Belt: the Lake Zone in the southwest, a northeast trending folded and thrusted volcano-sedimentary sequence, and the Kakamega Dome in the northeast, a wide synclinal structure of volcano-sedimentary rocks.

Deposits at Bushiangala and Isulu

Gold mineralisation at the Isulu and Bushiangala deposits is hosted by sheared pillowed to massive basalts, bordered between ultramafic volcanics and polymictic conglomerates on one side and carbonaceous mudstones and sandstones on the other side. The deposits are found in the Liranda Corridor area, a 12-kilometer structural trend on the eastern limb of the Kakamega Dome, a large synclinal structure with granitoids and diorites intruding in the centre. Within the mineralised shear zones, veinlets of quartz and quartz-carbonate with a true width of 0.5 to 10 meters are linked to mineralisation. The mineralisation style is categorised as an orogenic quartz-carbonate vein subtype that is hosted in shear zones.