Abstract
Mineragraphic study of the Early Proterozoic uraniferous oligomictic quartzpebble conglomerate of Walkunji reveals 'three types of uraninites, designated as U-I, U-II and U-III respectively. Textural and mineralogical characteristics indicate . that (i) U-I with plenty of filled-in fractures is subrounded to rounded in shape, detrital, allogenic and oldest in the sequence; (ii) U-II and U-III are authigenic with fine-grained U-II, occurring as fillings in gangue minerals, and appear to be hydrothermal; and (iii) colloform-textured U-III (pitchblende) is the youngest formed at low temperature due to remobilization of earlier phases. In addition, a little detrital, partially altered brannerite occurs with anatase.
Among the sulphides, melnicovite-pyrite and pyrite-marcasite are the most dominant followed by galena pyrrhotite and marcasite. The oxide sulphide mineral assemblage suggests that mineralization was primarily strata-bound in the initial stages followed by hydrothermal phase and ended with remobilization that resulted in the formation of U-lIl. The textural relationships among different ore minerals indicate the following paragenetic sequence: U-I, brannerite, pyrite, melnicovite-pyrite and gel. pyrite (oldest); U-II, arsenopyrite, pyrrhotite-marcasite, chalcopyrite, galena, sphalerite and molybdenite; and U-lIl, gel-pyrite and marcasite (youngest).
