Regolith research in support of mineral exploration in Australia

Abstract

Parts of the Australian continent have been emergent for some 2 Ga, and many of the landscapes have their origins 300 Ma ago. During this long history the rock sequences have been subjected to a wide range of climates including glacial, humid temperate, tropical, and arid, and to tectonic events. The resulting regoliths are complex in their stratigraphy, and associated chemical and mineralogical properties. A review of current regolith research is presented with emphasis on those aspects that influence mineral exploration and, in particular, exploration geochemistry. To replace ore deposits being mined, the mineral industry in Australia (and world wide) is vitally concerned with locating new mineral resources. The surface expressions of ore deposits are commonly altered beyond visual recognition in regolith-dominated terrain, concealed beneath duricrusts, or buried beneath cover sequences. This need for new mineral discoveries is the driving force behind much of the regolith research in Australia. Some key issues facing the mineral industry are: (1) Do buried ore deposits have a surface or near-surface expression? (2) What methods can be used in exploring through Phanerozoic basin cover? (3) Can large ore systems be recognised and distinguished from minor occurrences at the prospect stage? Processes of regolith formation, landscape evolution and geochemical dispersion are inter-linked and approaches to research can commonly reflect this relationship. From the perspective of regolith and landscape evolution, some of the most prominent current research issues are: providing a reliable time frame for weathering, exposure and burial; establishing the climatic history; methods for regolith mapping; standardising regolith terminology; understanding carbonates in the landscape. Developing research trends include reconciling the record from sedimentary basins with that from corresponding uplands; and reconciling the marine record with the weathering history of the continent. Research in exploration geochemistry is addressing each of the three exploration issues mentioned above. A further common practical issue being addressed is the difficulty of being able to tell, from drill spoil, a buried weathered profile from transported cover. Findings can be summarised into appropriate geochemical dispersion models. The most comprehensive sets of models are those established for the Yilgarn Craton in Western Australia. These are currently being extended into areas of complex surficial cover in the Yilgarn. Further research is directed at developing comprehensive knowledge of regolith-landscape evolution and geochemical dispersion in other parts of the Australian continent, including highly prospective regolith-dominated regions of Queensland, central and western New South Wales, South Australia and the Northern Territory. One of the striking developments in Australia in regolith research in support of mineral exploration over the last decade, is the emergence of sizeable, well-focussed, interdisciplinary research projects supported by a mixture of substantial industry and government funding. The majority of these projects have been coordinated through the Australian Mineral Industries Research Associates Limited (AMIRA). A substantial new initiative is the formation of the Cooperative Research Centre for Landscape Evolution and Mineral Exploration (CRC LEME). Core participants in the CRC are the regolith-geochemistry groups from the Australian National University, the University of Canberra, Australian Government Survey Organisation (AGSO) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Division of Exploration and Mining. The Centre brings research, development, applications, education and training together to provide a national focus on landscape evolution for mineral exploration. Regolith-landscape research in Australia is very much inter-disciplinary. It is undergoing considerable growth particularly in response to the needs of the mineral industry and has been facilitated by recent successful applications contributing to ore deposit discoveries. The regolith realm is now widely recognised as a major exploration and research frontier, both nationally and internationally.