Hidden Copper, Lead and Zinc Riches Traced to Ancient Granites in Northeastern Nigeria

Deep beneath the rolling hills of Bauchi State in northeastern Nigeria, a Jurassic-age granite complex may be hiding one of the region’s most promising base-metal deposits. A new whole-rock geochemical study of the Tongolo area has confirmed that the granites there belong to the chemically distinctive A-type family, and that the same magmatic machinery that built these rocks also concentrated copper, lead and zinc into economically intriguing anomalies. The findings, published in Discover Geoscience, transform a corner of the Nigerian Younger Granite province long known mainly for tin and niobium into a high-priority target for base-metal exploration.

The Nigerian Younger Granite province is one of the world’s classic examples of anorogenic magmatism. It comprises 53 distinct silica-oversaturated syenite-granite ring complexes spread across roughly 7,500 square kilometres within a north-trending belt about 400 kilometres long and 160 kilometres wide. These complexes were emplaced into the Precambrian Nigerian Basement Complex during the Jurassic period, with radiometric ages ranging from approximately 147 to 173 million years. Geologists interpret the province as the product of within-plate magmatism linked to the early opening of the South Atlantic Ocean, meaning the alkaline igneous activity was decoupled from the compressional forces of subduction zones. Individual complexes typically display multiple intrusive phases, from earlier basic and intermediate rocks to later, highly evolved granites and rhyolites, reflecting progressive fractional crystallisation of mantle-derived or hybrid melts.

The Tongolo area, located in Toro Local Government Area about 80 kilometres southeast of Bauchi city, sits within the broader Jos Plateau-Bauchi ring complex province. It has historically been recognised for tin-niobium mineralisation hosted in biotite granites. However, recent artisanal mining activity and reports of new base-metal occurrences prompted field investigations that confirmed the presence of lead, zinc and copper minerals. The area is underlain by three principal lithological units: the Tongolo Younger Granite Complex, composed of biotite granites, porphyritic granites and rhyolites; the Dagga-Allah Porphyry, a polygonal system of dykes cutting across the basement south of the granite complex; and the Palaeoproterozoic migmatite-gneiss basement reworked during the Pan-African Orogeny around 600 million years ago.

To characterise these rocks, the researchers collected seventeen representative samples from fresh outcrops across the roughly 282-square-kilometre study area during two years of fieldwork. After petrographic analysis at the University of Jos, the samples were crushed, pulverised and digested using a multi-acid mixture of hydrofluoric, nitric and perchloric acids to ensure complete dissolution of resistant minerals such as zircon and monazite. The resulting solutions were analysed for major and trace elements on an Agilent 4200 Microwave Plasma-Atomic Emission Spectrometer. Analytical accuracy was verified against certified reference materials, with recoveries for arsenic in the BGS 119 standard reaching 92.96 percent and relative standard deviations for key elements remaining below 3 percent across replicates.

The major-element results paint a clear picture of highly evolved, ferroan magmatism. The granitic rocks contain high silica dioxide, ranging from 68.50 to 75.25 weight percent with a mean of 72.66 weight percent, excluding a single dolerite sample. They also show elevated iron numbers, averaging 0.74, and low magnesium numbers averaging 36.56, a combination that is diagnostic of A-type granitoid affinity. On the Total Alkali-Silica classification diagram, the granites and rhyolites plot predominantly in the granite field, while the dolerite falls in the gabbroic diorite field. Harker variation diagrams reveal systematic negative correlations between silica and aluminium, iron, magnesium, calcium, manganese and phosphorus oxides, consistent with fractional crystallisation as the dominant differentiation process. Notably, the declining phosphorus trend points to early apatite fractionation, a mechanism widely recognised for generating metal-enriched residual melts in ore-forming granitic systems.

The trace-element data are where the story becomes genuinely striking. Compared with average upper continental crust, the Tongolo suite is dramatically enriched in uranium, with concentrations of 96 to 319 parts per million representing enrichment factors of roughly 35 to 118 times crustal values. Lead is enriched 4 to 19 times, zinc 3 to 37 times, and gallium about 4 times crustal abundances, while thorium, barium, vanadium, chromium and nickel are depleted. Primitive mantle-normalised spider diagrams show strong positive anomalies at uranium, lead and gallium alongside pronounced negative anomalies at barium, chromium, vanadium and nickel, a signature consistent with A-type affinity and advanced fractional crystallisation. Europium anomalies calculated for five viable samples range from 0.059 to 0.228, with a mean of 0.111, indicating extensive plagioclase fractionation characteristic of high-temperature, anhydrous A-type magmatic systems.

The base-metal concentrations themselves are remarkable. Lead was detected in every sample, ranging from 72.7 to 324.2 parts per million, indicating a consistent and widespread enrichment across the study area. Zinc spans a much wider range, from 154.7 to 8,537.9 parts per million, while copper varies from 10.6 to a staggering 20,498.7 parts per million. The extreme upper values for both zinc and copper occur in a single sample of pegmatitic granite-gneiss from Dagga-Allah, which records copper at approximately 2.05 weight percent and zinc at 0.85 weight percent, one to two orders of magnitude above the suite average. Elevated cadmium, reaching 72.8 parts per million in another sample, tracks the zinc enrichment and serves as a geochemical pathfinder for sphalerite-hosted mineralisation. Copper and zinc show a strong positive correlation of 0.77, pointing to a shared paragenetic control, whereas lead correlates only moderately with both, suggesting a broader and possibly earlier stage of lead mobilisation.

The spatial architecture of the mineralisation tells an equally compelling story. Kriging-interpolated anomaly maps for lead, zinc and copper, overlaid with lineaments interpreted from satellite imagery and field structural measurements, reveal that the highest concentrations of all three metals cluster in the southern sector of the study area, precisely where lineament density is greatest. Two dominant lineament orientations, northwest-southeast and northeast-southwest, coincide with structural trends identified in rose diagrams of joints and veins. Copper anomalies sit proximal to intrusive contacts, reflecting magmatic-hydrothermal fluid inputs, whereas lead and zinc anomalies are more widespread and structurally controlled, signifying distal dispersion by hydrothermal fluids migrating along the dominant lineament sets. High copper-to-lead ratios above 5, as seen in the Dagga-Allah sample, are generally associated with proximity to a high-temperature mineralising centre above 300 degrees Celsius, while distal expressions of the same system typically fall below 0.1 as lead becomes dominant.

Perhaps the most consequential insight concerns the origin of the controlling structures. The dominant north-northeast to south-southwest structural fabric mapped across all rock types aligns with regional Pan-African structural fabrics in the northeastern Nigerian basement. This suggests the brittle structures now hosting mineralisation were not generated by the Younger Granite emplacement itself but instead reactivated pre-existing basement-scale weaknesses inherited from the Pan-African orogeny. The implication for exploration is profound: similar structural corridors elsewhere in the Pan-African basement of northeastern Nigeria may represent comparable base-metal targets, independent of whether a Younger Granite intrusion is exposed at the surface.

The study’s authors acknowledge limitations, including an incomplete rare-earth-element dataset limited to five elements, the absence of isotopic or fluid-inclusion constraints, and the qualitative nature of the lineament analysis. Future work will integrate aeromagnetic data to map subsurface structural architecture, apply uranium-lead zircon geochronology to constrain the emplacement age of the Tongolo Complex, and conduct fluid-inclusion microthermometry to determine the temperature, pressure and salinity of the mineralising fluids. For now, the southern Tongolo sector stands as a high-priority exploration target, and the study adds fresh geochemical constraints on how A-type magmatism and magmatic-hydrothermal processes conspire to build base-metal deposits in one of Africa’s most distinctive granite provinces.

Subject of Research: Lithogeochemistry, petrogenesis and base-metal mineralisation of A-type granites in the Tongolo area of the Nigerian Younger Granite province

Article Title: Lithogeochemistry and petrogenesis of A-type granites and associated rocks from the Tongolo area of northeastern Nigeria and implications for lead-zinc-copper mineralisation

Article References: Olorunyomi, A. E., Olobaniyi, S. B., & Odukoya, A. M. (2026). Lithogeochemistry and petrogenesis of A-type granites and associated rocks from the Tongolo area of northeastern Nigeria and implications for lead-zinc-copper mineralisation. Discover Geoscience, 4(1), Article 326. https://doi.org/10.1007/s44288-026-00691-3

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00691-3

Keywords: A-type granite, Nigerian Younger Granite province, Tongolo complex, Pb-Zn-Cu mineralisation, lithogeochemistry, petrogenesis, fractional crystallisation, magmatic-hydrothermal fluids, lineament control, MP-AES, Bauchi State, base-metal exploration