Detecting and Characterising Illegal Mining Sites in the North Central Solid Minerals Belt Using SAR and Optical Remote Sensing

Illegal mining operations across Nigeria's North Central solid minerals belt in Niger, Kogi, and Kwara States deplete mineral resources, cause environmental damage, and generate substantial revenue losses to the Federal Government, yet systematic spatial monitoring of mining activity is absent from the current regulatory toolkit. This study develops a multi-sensor SAR and optical remote sensing methodology for detecting and characterising illegal mining sites across the North Central solid minerals belt. Sentinel-1 SAR coherence change detection is applied to identify surface disturbance signatures associated with excavation activities between 2021 and 2024, and Sentinel-2 spectral indices including the Clay Mineral Ratio and Ferric Oxide Ratio are used to characterise exposed geological materials at identified disturbance sites. High-confidence mining site candidates are validated using Planet Labs high-resolution imagery and field GPS surveys in accessible areas. Results identify 387 previously unmapped mining sites across the three-state study area, representing a 58 percent increase over the inventory maintained by the Federal Ministry of Mines and Steel Development. Spatial analysis reveals clustering along known cassiterite, columbite, and gold-bearing lithological units, with site density highest in Minna and Lokoja environs. The detection methodology achieves a precision of 86 percent and recall of 79 percent against field-validated ground truth. The study provides a scalable monitoring protocol for the Mining Cadastre Office and the North Central State Ministries of Solid Minerals. Keywords: illegal mining, SAR change detection, solid minerals belt, North Central Nigeria, remote sensing.