Magnetic and Electrical Resistivity Survey for Characterising Volcanic Rocks in Plateau State

This study applies combined magnetic and electrical resistivity methods to characterise volcanic rocks and map their distribution in Plateau State, North Central Nigeria. The Jos Plateau hosts a diverse volcanic complex including trachyte, basalt, ryholite, and phonolite intrusions and extrusions emplaced between the Jurassic and Tertiary periods. These volcanic rocks host tin, columbite, and rare earth elements and influence local groundwater flow by creating impermeable barriers or hydraulic conduits depending on their fracture state. This study acquires total magnetic intensity data along 20 profiles at 25-metre station spacing and Schlumberger VES data at 18 stations distributed across the volcanic terrain of Barkin Ladi local government area. Magnetic data are processed for diurnal correction, IGRF removal, and RTP transformation. First vertical derivative maps are computed for structural enhancement. VES data are inverted and interpreted for volcanic versus sedimentary layer discrimination based on characteristic resistivity signatures. Petrophysical reference data from outcrop samples supplement the interpretation. Findings reveal magnetic highs of 1,000 to 4,500 nanotesla associated with basaltic and phonolitic intrusions mapped at surface and confirmed by sampling. Rhyolitic and trachytic rocks show lower magnetic signature but high resistivity above 1,000 ohm-metres in VES data. The integrated interpretation produces a lithological map distinguishing mafic and felsic volcanic units and identifying tectonic lineaments that control the volcanic distribution. A newly identified northeast-trending mafic dike swarm not mapped in the existing NGSA 1:250,000 sheets represents a potential tin-cassiterite exploration target.

Keywords: volcanic rock mapping, magnetic survey, Plateau State, Jos Plateau, tin exploration.