Characterization and genesis of mineralized skarn types within the Tsauni metagranitoids, North-Central Nigeria

This study investigates the nature, mineralogy, and genetic characteristics of two distinct types of mineralized skarn occurring within the metagranitoids of Tsauni area, Abuja, north-central Nigeria. The work represents the first detailed examination of these skarn systems, aimed at assessing their potential as hosts for gold–sulphide and iron mineralization and providing insights into skarn formation processes within the Nigerian Basement Complex. The Tsauni lithologic assemblage comprises regionally metamorphosed gneisses, migmatites, amphibolites, and minor granitic intrusions with interlayered calc-silicate bands. Two endoskarn types were identified and designated as Type A and Type B. Type A is a pyroxene–amphibole–sulphide-rich skarn developed within felsic to intermediate bands, containing subordinate feldspar, biotite, epidote, chlorite, tourmaline, and wollastonite. Type B is a light rare earth element (LREE)–enriched, pyroxene–biotite–magnetite–copper-rich skarn with accessory apatite (> 1%), titanite, and zircon. Clinopyroxene and wollastonite represent prograde skarn minerals formed under high-temperature, high-pressure contact metamorphic conditions, while calcite is ubiquitous in both types. Electron microprobe results show that Type A minerals are aluminium-poor (hedenbergite, magnesiohornblende, actinolite), whereas Type B biotites are Ti-rich, equilibrated at > 600 °C and depth estimated at 4–6 kbar. Whole-rock geochemistry (ICP–ES/MS) indicates metasomatic alteration marked by mobility of alkali, alumina, and LIL/HFS elements. Stable isotope compositions (δ13C and δ18O) of calcite plot between magmatic and metamorphic/skarn fields, suggesting that late-magmatic, hydrothermally induced metasomatism of the metagranitoids during the Pan-African orogeny was responsible for the skarnification. These findings demonstrate that Tsauni hosts significant skarn systems with potential for Au- low sulphides (Pb–Zn–Cu) and iron (magnetite) mineralization that require further detailed exploration. The available data from the present study forms an important baseline information for future study and discovery of other skarn deposits across Nigeria.