On the Genesis of the Lower Benue Valley Lead-Zinc Deposits, Southeastern Nigeria: Inferences from Carbon, Oxygen and Hydrogen Stable Isotopes Studies

摘要

The Benue Trough is a metallogenic province consisting of numerous occurrences of lead-zinc, barite-fluorite deposits distributed in three principal districts at the upper, middle and lower Benue Valley in Nigeria. Ore stage Pb and Zn sulfide and post-sulfide silicate and carbonate minerals are hosted by black carbonaceous shales in the lower Benue where the sediments locally attain a thickness of about 2000 m. Carbon, oxygen and hydrogen isotopic measurements have been carried out on the carbonates (C, O) while the δD isotopic composition of sphalerites and quartz are also determined with a view to determine the origin of the lower Benue lead- zinc mineralization.The δ 13C isotopic composition of the carbonates range from -2.0 to -5.2 per mil, and a mean of -2.8 per mil. And the δD values in post-sulfide quartz ranges from -35 to -40 per mil, with an average of -37.5 per mil which implicates derivation from the oxidation of organic matter in the black carbonaceous shale while water in the inclusions are basically meteoric in origin with possible minor sea water input.