Lead Isotopic Variation and Sources of the Lead in the Lead-Zinc Mineralization of the Benue Trough, Nigeria
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The Nigeria Benue Trough, an elongated sediment-filled rift initiated during the Cretaceous continental drifting and opening of the Atlantic Ocean is subdivided into three segments namely, the Lower Benue (LB), Middle Benue (MB) and Upper Benue (UB) Trough. Sulfide deposits including galena, sphalerite, chalcopyrite and pyrite occur within black carbonaceous shales and mudstones intercalated with layers of limestones in the Lower Benue at Isiagu, Ameri, Ameka, Enyigba, Akpatakpa and within arkosic sandstones at Zurak in the Upper Benue. At Arufu and Akwana, barite and fluorite mineralisation are hosted by platform carbonates in the Middle Benue Trough. Lead isotopic composition across the Benue Trough showed three discrete lead isotopic variations,Isiagu deposit designated as LB1, Ameri, Ameka, Enyigba, Akpatakpa deposits labelledas LB2 with Zurak deposits as UB and Arufu and Akwana deposits as MB Groups. The lead isotopic composition of Group LB1 ranged from 17.52 -17-70 for Pb/ Pb and 206 208 204 204 38.26 – 38.43 for Pb/ Pb.The mean isotopic composition for both the uranogenic and thorigenic leads from Group LB1 is 17.63 and 38.31 respectively. The LB 2 + UB Group showed an isotopic composition of 17.93-18.08 for 206 204 208 204 Pb/ Pb and 34.14 – 38.49 for Pb/ Pb with a mean of 17.83 and 38.34 for the uranogenic and thorigenic components respectively. The lead isotopic composition of the MB Group rangedfrom 18.15 – 18.26 for Pb/ Pb 206 208 204 204 and 38.86 – 38.87 Pb/ Pb with a mean of 18.19 and 38.86 for the uranogenic and thorigenic components respectively. The Benue deposits are notable for their low radiogenic character and homogenous Pb/ Pb and Pb/ 207 204 208 204Pb ratios. These results imply that no single source of lead was overall dominant throughout the Benue Trough. The LB2 + UB deposits had inputs from basaltic rocks and granitoids from the Lower and Upper Benue Trough.Lead LB1 wassourced from the mantle. The Benue Trough deposits gave a wide range of model source ages between 500-300 ma indicating heterogeneoussources of materials.
Publication Info:
Author: Ogundipe, I.E., Ogundana, A.K., Afolabi, O.O. and Olutomilola, O.O.
Volume: 53
Issue: September
Published By: Journal of Mining and Geology, 2024-09-01