Geological, Geochemical and Mineralogical Investigation of Sakpe Ironstone around Jima, Northern Bida Basin, Nigeria

Abstract

The geology, geochemistry and mineralogy of the Sakpe Ironstone were studied around Jima, Northern Bida Basin, Nigeria. The ironstone was logged in relation to the overlying and underlying formations and ten (10)well labelled representative samples of the ironstone formation were collected. These samples were taken to the laboratory for analysis using XRF and XRD techniques. Thin sections of five (5) of the sample were also prepared and studied under a petrological microscope. The ironstone is reddish-brown in colour and this appearance is due to oxidation. The texture of the ironstone is oolitic and pisolitic with a gradation from the former to the latter. The diameters of the oolites range from 0.08 to 1.95mm while those of the pisolites range from 2.0 to 6.0mm. Sedimentary structures that were observed include parallel laminations and some local occurrence of wavy beddings. The result of the chemical analysis revealed that the ironstone contain an average of 58.9wt% Fe, 28.94wt% Si and 12.91 % Al. The average concentrations of P, K, Ca, Ti, Mn, Mg, and Na are 0.03wt%, 0.002wt%, 0.071wt%, 0.177wt%, 0.184wt%, 0.027wt% and 0.008wt%respectively. The results show that the ironstones are of high grade, having iron content > 54 % set by the Natural Resources Canada. Similarly, the low Mg (MgO wt %) content of between 0.01 and 0.051wt% and absence of sulphur in the samples suggests that the ironstones were not deposited in a fully marine environment; perhaps they were deposited in a non-marine to shallow marine environment. Mineralogical analysis showed that the ironstones contain goethite and hematite as the major phases with kaolinite and quartz as impurities. The petrological analysis showed that the structure of the iron bearing minerals are in form of river lines and plates which are the characteristics of goethite and hematite. The result of the XRD and the petrological analysis both confirmed that the studied Sakpe ironstone is predominantly goethite and hematite iron bearing minerals from which a high grade iron ore can be mined.