Geophysics, geochemistry and engineering geology: how disciplines combine to improve mine slope design in the Pilbara detrital valleys of Western Australia

Abstract Cenozoic age detrital sequences in the Pilbara region of Western Australia are becoming a focus for engineering geological and hydrogeological investigations with an increasing number of final open-pit walls developed in these materials for iron ore mining. Historically, detrital sequences were classified chronostratigraphically. However, within each chronostratigraphic unit exist sub-units of variable engineering geological and hydrogeological character. As the majority of drill-hole data from Pilbara iron ore mines is derived from reverse circulation techniques, a methodology to identify the engineering geological units through downhole geophysics and geochemical assays was required to progress model development to the level of detail required for geotechnical and hydrogeological studies. The methodology entails a review of cored hole data and use of twin holes to assess the typical geochemical and geophysical signatures of units identified. Improved interpretation of reverse circulation drill-holes has resulted in the development of detailed 3D engineering geological models, which have improved the understanding of geological variability and engineering properties for geotechnical and hydrogeological studies.