Petrographic study of the Pb- Zn Ore from Gwana in the Upper Benue Trough.

Abstract

The Pb–Zn (lead–zinc) sulphide mineralization within the Benue Trough extends from 
the Lower Benue to the Upper Benue Trough, indicating a widespread metallogenic 
belt. Representative ore samples from this region were examined using Scanning 
Electron Microscopy (SEM) to investigate their mineralogical and petrographic 
characteristics. Petrographic analysis reveals that the mineralization is 
predominantly composed of Galena (PbS) and Quartz (SiO₂), with minor occurrences 
of Chalcopyrite (CuFeS₂), Magnetite (Fe₃O₄), and trace aluminosilicate minerals. 
During later stages, under near-surface and oxidizing conditions, significant 
replacement processes occurred. Galena was partially replaced by Anglesite (PbSO₄), 
while associated copper-bearing minerals underwent alteration. The movement of 
copper-rich solutions through the deposit led to the formation of thin, persistent 
bands of Covellite (CuS), often found within or adjacent to Anglesite zones. These 
formed contemporaneously with the oxidation of Galena. Chalcopyrite was similarly 
affected by oxidation, transforming into Covellite, whereas Magnetite and Pyrite 
(FeS₂), where present, remained largely unaltered, suggesting their relative 
resistance to oxidative weathering. Backscattered SEM imaging identified two 
distinct types of Galena: altered and unaltered. Further petrographic analysis in 
polished sections revealed three main textural varieties of Galena: cubic, fibrous (or 
gneissic), and granular. These textures provide insights into the paragenesis and 
post-depositional alteration history of the Pb–Zn mineralization in the Benue Trough.