stripes
Sekululu lies just to the west of Mount Elgon and forms a small group of hills. It consists essentially of a central plug of feldspathic agglomerates and tuffs which are enveloped on three sides by ijolitic rocks. Three areas of carbonatite have been located on the western side of the complex. There is a very broad aureole of fenitization and fenites do outcrop, whereas all the other rocks of the complex are obscured by thick residual soils, their distribution having been determined by geochemical soil surveys and drilling. The agglomerates are deeply weathered and composed mainly of fine-grained K-feldspar with accessories including ilmenite, magnetite, perovskite, apatite, fluorite and zeolites. Silicification is locally extensive. The ijolites lie beneath a broad valley surrounding hills of agglomerate and are variably fine- to coarse-grained, and contain melanite, biotite, and nepheline partly altered to cancrinite. They are cut by thin carbonatite dykes. The carbonatites are sovites with a little biotite and apatite, pyroxene and tremolite being locally abundant; pyrite, pyrochlore and magnetite also occur. Associated with the carbonatites are ferruginous phosphatic rocks composed principally of secondary phosphates. Shattering and shearing of the Precambrian basement rocks extends for up to 3 km from the complex with the fenitization characterized by the development of blue sodic amphibole. A gravity survey (Reedman, 1974) indicates that the complex probably takes the form of a vertical cylinder. Reedman (1974) also gives the results of an extensive geochemical survey of the residual soil cover.
DAVIES, K.A. 1956. The geology of part of south-east Uganda. Memoir, Geological Survey of Uganda, 8: 1-76.REEDMAN, J.H. 1974. Residual soil geochemistry in the discovery and evaluation of the Butiriku carbonatite, southeast Uganda. Transactions of the Institution of Mining and Metallurgy, 83: B1-12.