Guide horizons for gold mineralisation in lateritic crusts

The structural classification previously proposed for laterite crusts in field exploration by the author has the objective of: (a) serving as a tool to geological mapping of the bed rock types; (b) recognition of greenstone belt units of economic interest; and (c) demarcation of target areas for mineral exploration. In localities of several small placer gold operations, outcrops of nodular and pisolitic laterite crusts are seen overlain occasionally by breccioid laterite, nodular laterite breccia, mottled cavernous laterite or banded concretionary laterite. Such nodular or pisolitic varieties, rich in goethite, characterise mafic to ultramafic parent rocks in/and greenstone belt units. This type of crust is thus the guide horizon in the laterite profile indicative of Au. Its surface expression accompanying the source rocks is occasionally significant and thus can be a promoter of small-scale mining and a metallotect and guide for exploration programmes.