Conceptual models in exploration geochemistry

Abstract

This is the fourth in a series of “Conceptual Models” volumes reviewing geochemical exploration practice in different areas of the world. This volume provides an overview of geochemical exploration for base and precious metals in Australia. The subaerial weathering history of most of the continent probably dates from the Permian including, broadly, an early period of widespread lateritization followed by a late trend to aridity. This gave rise to the formation of a deep weathering profile which may subsequently have been partially or wholly eroded. It differs markedly, therefore, from the terrains described in previous volumes in the series. Consequently, emphasis has been placed throughout on the long weathering history, and the influence it has had on element dispersion and on the surface expression of mineralization in a wide range of sample media - ironstones, gossans, weathered bedrock, soils, transported overburden, stream sediments, waters, plants and atmospheres. The nature, use and geochemical characteristics, including multi-element data where possible, are described for each of these sample media. A set of eight idealized models has been derived using data from fifty-two case histories and previously published literature. The models are based on generalized landform settings, classified hierarchically according to: 1. (1) degree of preservation of the deep weathering profile, i.e. complete, partly stripped or absent; 2. (2) relief, i.e. low, moderate or high. A further model describes the landform situation within which calcrete uranium deposits are formed. The case histories present, for the most part, previously unpublished data and include examples not only of successful exploration but also situations where surface anomalies are spurious.