Evaluation of kaolin deposits in Maastrichtian formations of the afikpo basin, southeastern Nigeria

Abstract

The study area lies within latitude 5^o20ˈ to 6^o00ˈN and longitude 7^o40ˈ to 7^o60ˈE. Kaolin or china clay, a pure, soft, white clay of variable but usually low plasticity that retains its white color when fired. The chief constituent of kaolin is the mineral kaolinite, a hydrous aluminum silicate, Al2Si2O5(OH)4, formed by the decomposition of aluminum silicates, particularly feldspar. Kaolinite is the dominant clay mineral in both Formations followed by minor amounts of illite and montmorillonite. The plasticity values show samples no. (AMV2, NKA2 and NKA 3) were medium plastic, samples no. (AMV1, OBO1, OBO2, OKO, NKA1 and AMA) are low plastic, clays with plasticity, permits it to be shaped or moulded when mixed with water, and have sufficient wet and air dried tensile strength to maintain their shape after forming. Kaolinite values ranges from 70.40 to 80.00% as the major clay mineral present in both Formations. It mainly occurs in open environments with high acidic content. Under acidic, warm, tropical conditions, smectite and marine type clay lose their characteristic ions (K⁺ Na ⁺, Ca²⁺, and Fe²⁺) while H⁺ is added to produce kaolinite. Due to its stability in low Ph waters, it may be converted to illite during diagenesis in the presence of alkaline connate water.

Keywords: Kaolin, Mineral, Evaluation, XRD, Maastrichtian, Afikpo.