Determination of rare earth elements concentration at different depth profile of Precambrian pegmatites using instrumental neutron activation analysis

Highlights: • NAA was used to investigate the concentrations of REEs in pegmatite of Keffi. • No statistically significant europium anomaly in all depth profiles of the pegmatite. • The analysis has shown that the pegmatite is enriched with light REEs. • There were significant deviations in the lanthanum to lutetium ratios and the ratio were about an order of magnitude higher than that of chondrites. - Abstract: The Keffi area hosts abundant pegmatite bodies as a result of the surrounding granitic intrusions. Keffi is part of areas that are geologically classified as North Central Basement Complex. Data on the mineralogy and mineralogical zonation of the Keffi pegmatite are scanty. Hence the need to understand the geology and mineralogical zonation of Keffi pegmatites especially at different depth profiles is relevant as a study of the elemental composition of the pegmatite is essential for the estimation of its economic viability. Here, the relative standardization method of instrumental neutron activation analysis (INAA) has been used to investigate the vertical deviations of the elemental concentrations of rare earth elements (REEs) at different depth profile of Keffi pegmatite. This study adopted the following metrics in investigating the vertical variations of REEs concentrations. Namely, the total contents of rare earth elements (∑REE); ratio of light to heavy rare earth elements (LREE/HREE), which defines the enrichment or depletion of REEs; europium anomaly (Eu/Sm); La/Lu ratio relative to chondritic meteorites. The study showed no significant variations in the total content of rare elements between the vertical depth profiles (100–250 m). However, higher total concentrations of REEs (~ 92.65 ppm) were recorded at the upper depth of the pegmatite and the europium anomaly was consistently negative at all the depth profiles suggesting that the Keffi pegmatite is enriched with light REEs.