Rare Earth Element Geochemistry of Soils in Southwestern Part of Sheet 272 Katsina-Ala SE, North Central Nigeria

Abstract

Following a reported enrichment of Rare Earth Elements (REE) from a regional stream sediment survey in parts of north central Nigeria, a medium density geochemical soil survey was carried out around Ushongo area of Benue State, Nigeria. This was with a view to assessing the REE mineralization potential of the study area. A detailed geological fieldwork was carried out in which three (3) rock types were identified - medium grained granite, amphibolite and migmatite gneiss. Sixty (60) soil samples were collected within the delineated area and analysed using the ICP-MS method. The soil geochemical data obtained were subjected to statistical analysis involving Pearson correlation and R-mode varimax rotated factor analysis techniques. The element distribution and trend maps were plotted using ArcGIS software. The total REE in ppm ranges from 232.7 to 1092.7. The REE concentrations (in ppm) revealed higher concentrations of the light REEs (216 – 1041 ppm) compared to the heavy REEs (12.61 – 52.67 ppm). Within the REE’s; Ce, La, Nd, Th, Pr, Sm, shows positive correlation between each other with a significant value of 0.5 and above which interprets a strong association and a possibility of a common source of mineralization. The factor analysis enabled separation of elements into three factors and of the three associations only the Ce-La-Nd-Pr-Sm-Th (factor 2) is considered related to metallic mineralization. Furthermore, the aforementioned associated elements (Ce, La, Nd, Th, Pr, Sm) showed significant anomalous values when interpreted which were considered to be derived from primary mineralization of these elements. The concentration maps of these light REE’s reveals a pattern that shows a similar trend of high concentration (670ppm, 232ppm, 213ppm,etc) and coupled with their strong correlation, a critical observation suggest a possible mineralization of Monazite (Ce, La, Nd, Th)(PO4,SiO4).