Study of Ore Grade Variability and Its Implications for Production Planning at a Columbite-Tantalite Mine in Nassarawa State

Columbite-tantalite (coltan) mining in Nassarawa State, North Central Nigeria, is characterised by significant spatial variability in ore grades that complicates production planning and revenue forecasting for small-scale operators. This study investigates the nature and extent of ore grade variability at a representative coltan mine in Nassarawa State and assesses its implications for production scheduling. A total of 85 channel and chip samples were collected along systematic grid lines across the mineralised zone. Samples were analysed for niobium and tantalum pentoxide content using X-ray fluorescence. Variogram analysis and ordinary kriging were applied to model spatial grade distribution. Results reveal a nugget effect contributing approximately 40 percent of the total spatial variance, confirming high short-range grade variability typical of placer-type coltan deposits. Grade blocks estimated by kriging show ore tonnes within economic cut-off grade to be clustered in the southern and eastern portions of the deposit. The study demonstrates that selective mining guided by grade control sampling can improve product quality and profitability by 30 percent compared to bulk mining approaches. Recommendations include the adoption of structured grade control protocols and investment in portable X-ray fluorescence analysers for on-site assay. This research provides an accessible framework for grade management applicable to similar artisanal and small-scale coltan operations across North Central Nigeria. Keywords: columbite-tantalite, ore grade, Nassarawa State, kriging, production planning.