Characterisation of apatite and secondary phosphate minerals in Sukulu phosphatic soil, Uganda

Abstract

The Sukulu deposits were first discovered to be of economic signifi¬cance in the 1950's which is a ring carbonatite complex of S kin in diameter. Although the original carbonatite has been considered subeconomic, leaching and watering of the rock has resulted in over 200 million tons of residual soil, rich in apatite, magnetite and other heavy minerals. The sample, in general, made up of fines and friable concretions heavily coated with ferruginous and lintonitic materi¬als. The X-ray powder diffraction of the soil indicates the presence of apatite as a dominant, primary phosphatic phase, the cell param¬eters of which are almost in between pure fluor and hydro.xyl¬apatite end members. Refractive index (R..1.) .study, geochemical analysis and X-ray mineralogy indicate that the apatite is of mixed composition with fluorapatite structure and bear a close resent¬blance to that of apatite from Beldih, Purulia district, West Bengal. Crandallite is the major secondary phosphatic phase associated with govazite and gor-ceixite. Magnetite (martitised along the cleav¬age plane and fracture plane), hematite, quartz, limonite and maghemite are the major gangue minerals. Ferrocolumbite, pyrochlore, zircon and limonite are the heavy minerals that are present in the sample. The liberation study shows that most of the composite grains (iron minerals + silicates) are concentrated above 100 mesh fractions while most of the free apatite are within the size range of 100 to 200 mesh.