Ceramic parameters in the financial evaluation of brick clay deposits, with reference to two South African examples

by Perold, Jacques.

Brick clay deposits, in the area north of Cape Town, were formed as a result of three independent geological processes. The intrusion of the syn- to post tectonic granitoids into micaceous (indicated by the absence of halloysite; Orris, 1998), feldspathic Malmesbury sandstone beds, approximately 500 Ma ago, created a hydrothermal vein structure, which enriched the shale with feldspar/kaolinite and quartz, restricted to the vein network. This was followed by extensive in-situ weathering of these hydrothermally altered rocks resulting in residual kaolin deposits, the effects of which were more pronounced along the more permeable shear zones. The final process, formation of ball clay deposits, initiated by the erosion of the primary kaolinite deposits, which have been transported in water, together with organic material, to shallow depressions where clays were deposited. Brick clay is exclusively used for the manufacturing of clay brick products and must derive its value from the sales revenue generated from these products. Evidence from the two exploration programs described, suggests that the clay deposits explored has no value as individual deposits as the clay from both deposits lack specific ceramic properties to successfully manufacture clay bricks. It is however clear that if the clay from the two deposits is mixed in specific proportions; body mixes with ceramic properties suitable for light coloured clay face brick manufacturing is possible. The value of the beneficiated product, clay bricks, may then be used to determine the value of both clay deposits. Discounted Cash Flow Models (DCFM) and Net Present Values (NPV) were used to determine the fundamental value of the clay deposits explored, as it determines the time value of money (Kernot, 1999). These models clearly showed the dependency of the value of clay brick deposits on variables such as raw material quality, capital expenditure and clay brick yields. Geological, chemical and ceramic knowledge of individual brick clay deposits and the management of the raw materials extracted from these deposits is key to the profitable iv manufacturing of clay bricks. Risks, at the quarrying level, related to these aspects need to be managed to ensure the profitable and efficient functioning of the entire brick production process. v