GRIN Verlag Review of Geology, Geochemistry and Origin of Gypsum Mineralization in Chad Basin (North Eastern Nigeria): Origin of Gypsum Mineralization by Brine Mixing Hypothesis

Research Paper (postgraduate) from the year 1998 in the subject Geography / Earth Science - Geology, Mineralogy, Soil Science, grade: Research, Abubakar Tafawa Balewa University (Geology Programme), course: Economic Gelogy/ Mineral Exploration, language: English, abstract: A field trip was conducted in order to evaluate the geology, geochemistry and origin of gypsum mineralization in the Nigerian sector of Chad Basin, part of which is the research area. The gypsum mineralization underlain the whole area of about 2247.75km2 within the Chad Basin and comprises of five different forms; Detrital, Balatino - Laminated, Selenite, SatinSpar, and Alabaster. The thickness of the gypsum forms increases with depth, and they are emplaced at various depths. All the gypsum forms retained traces of former lamination except detrital gypsum therefore lamination is a primary structure.The chemical composition of the gypsum forms showed that they are all high grade (over 70% CaSO4 . 2H2O). The moisture content could be used to show fractured areas where circulation of water is easier. Alabaster gypsum is the heaviest as such more suitable for cement works. The chemical composition of all the gypsum forms revealed high trace elements content which could be the product of the brine mixing phenomenon. The petrographic studies of the Balatino, Selenite, SatinSpar and Alabaster gypsum forms revealed that they all recrystallized from the primary laminations during the early diagenesis. The recrystallization appeared to be perpendicular to the primary laminations. There are dissemination of anhydrite in the matrix of the gypsum forms which shows the effect of incomplete rehydration after upliftment. The origin of gypsum mineralization in Chad Basin is both sedimentary and diagenetic, so based on high trace element content and primary lamination, a brine mixing hypothesis was proposed for the origin of the gypsum mineralization in the Chad Basin.