Unravelling Gold Mineralization Pathways in a Pan-African Basement Terrane: Integrated Evidence from Geochemistry, Mineral Inclusions and Gold-Grain Chemistry

Abstract

Abstract: Even with growing evidence of considerable mineral potential in southeastern Nigeria, a key challenge is understanding the origin and metallogenic evolution of gold mineralization in the Obudu Plateau–Boki–Oban Massif of the southeastern Nigerian Basement Complex. This study combines stream-sediment geochemistry, mineralogical characterization, multivariate statistical analysis, and gold-grain microchemistry to establish the genesis of gold and associated mineralization in the region. Trace elements in representative samples of stream sediment, soil, and rock were analyzed by inductively coupled plasma–mass spectrometry (ICP–MS), and gold grains and associated mineral inclusions were examined by scanning electron microscopy (SEM–EDS), X-ray diffraction (XRD), and electron probe microanalysis (EMPA). Geochemical results indicate substantially elevated Au levels (up to 0.56 ppm), along with anomalous As, Sb, Pb, Sn, Nb, Y, and rare-earth elements, suggesting contributions from hydrothermal and evolved granitic mineralizing systems. Principal Component Analysis revealed distinct Au–As–Sb and Nb–Sn–REE associations, indicating different metallogenetic processes. Gold grains are mostly sub-rounded, with Ag-depleted core-rim textures suggesting proximal transport and supergene modification. EMPA analyses show fineness values from 936 to 1000 in Oban and from 990 to 996 in Besenge. Cassiterite inclusions in the Oban gold grains, with minor Cu enrichment and variable fineness, indicate derivation from a granite-related magmatic-hydrothermal Au-Sn system. In contrast, the euhedral LREE-rich, low-Th monazite inclusions and the consistently high-fineness gold of Besenge are typical for structurally controlled orogenic metamorphic-hydrothermal mineralization. Integration of geochemical, mineralogical and microchemical data indicates co-occurrence of granite-related Au–Sn and orogenic gold systems in the study area. These findings provide the first integrated metallogenic framework for the Obudu Plateau–Boki–Oban Massif and identify priority exploration targets for gold, tin, niobium and rare-metal mineralization in southeastern Nigeria.