Clay minerals are a group of fine-grained phyllosilicate minerals that form primarily through weathering and hydrothermal alteration of silicate rocks, and are commonly encountered in ore deposits and overburden profiles across bauxite, gold, iron ore, and diamond mining operations. The principal clay mineral groups include kaolinite, montmorillonite (smectite), illite, chlorite, and halloysite, each exhibiting distinct chemical compositions, crystal structures, surface charge properties, and behaviours in mining and processing environments. In bauxite deposits, kaolinite and gibbsite co-occur, but kaolinite and other reactive silica-bearing clay minerals represent undesirable gangue that depletes caustic in the Bayer Process and must be minimized through beneficiation or ore blending. In gold deposits, clay minerals derived from argillic alteration zones can cause significant processing difficulties including viscous slurries, preg-robbing of dissolved gold by carbonaceous or clay surfaces, and reduced leach recovery. In iron ore deposits, clay minerals such as kaolinite occur as intergrowths with hematite and goethite, reducing iron grade and necessitating washing or flotation for removal. In kimberlite diamond deposits, smectite-rich clay minerals derived from alteration of primary kimberlite phases (olivine, phlogopite) form a challenging, swelling clay matrix that is difficult to scrub and process efficiently. Clay mineral identification is performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy.
