This paper presents and reviews the processes responsible for the distribution and formation of regolith and associated landscapes of the Yilgarn Craton and highlights their implications for mineral exploration. It provides an analysis of regolith geology investigations that were conducted in many districts of contrasting contemporary geomorphic and climatic conditions. The Yilgarn Craton is composed of Archaean rocks, predominantly granitoids, that are crossed by north‐northwest‐trending belts of greenstones. It has an arid to humid climate at present. The gently undulating landsurface forms a partial etchplain and the topography is largely related to bedrock lithologies and a complex history of valley development and aggradation. Deep weathering has affected most lithologies and geological provinces across the craton. The depth of the weathered mantle may be as much as 150 m, but it varies considerably and rock outcrop may occur in any part of the landscape. The main factors influencing extent of weathering are rock type, mineralisation and deformation. Palaeomagnetic dating of deeply weathered regolith profiles suggest that they formed throughout the Phanerozoic. An idealised profile commonly comprises fresh bedrock, grading upwards into saprock and saprolite, commonly bleached towards the top, especially on felsic or sheared mafic rocks. This is overlain by a clay‐rich and/or quartz‐rich zone, a mottled zone and a ferruginous, bauxitic or siliceous upper zone. These horizons are formed by a combination of weathering and landscape processes. Landscape processes would have been continuous throughout the weathering period, with major environmental changes triggering particular erosional and depositional events. Thus, upper horizons, mottled zone, ferruginous duricrust and silcrete have developed in residuum, colluvium and alluvium of various ages. Weathering is the result of interaction between the hydrosphere, biosphere and lithosphere. During weathering some of the components of primary minerals are leached and secondary minerals are formed as residua. The pathways by which these minerals form are varied and complex. Biota were present in the regolith and it is likely that they and their associated chemical reactions played a significant part in the weathering process, as well as inorganic chemical processes. The final product of weathering of all rocks is a mineral assemblage of least soluble minerals (kaolinite, hematite, goethite, maghemite, gibbsite, anatase and boehmite) and the most resistant primary minerals (quartz, zircon, chromite, muscovite and talc), although neoformation of several generations of hematite, goethite, kaolinite and gibbsite may occur. Poorly crystalline minerals are an important constituent in surface or near‐surface materials. In addition, the more soluble minerals, including carbonates, sulfates and halides, occur in arid environments. The principal effects of weathering on element distributions relates leaching and retention of a range of elements to mineral transformations in th...

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Ferruginous regolith materials are abundant and widespread in the Yilgarn Craton of Western Australia and have been successfully used as sample media in Au exploration. However, their formation has been complex. They are developed in residual and transported materials of various ages. Four general types are recognized: ferruginous duricrust and gravel, ferruginous mottles, ferruginous saprolite and iron segregations. Ferruginous duricrusts include lateritic residuum and ferricrete. Lateritic residuum has evolved by partial collapse of mottled or ferruginous regolith, involving local vertical and lateral (generally 10–50 m) movements after chemical wasting. Ferricretes are ferruginized sediments. Some are detrital clasts cemented by Fe oxides and others are authigenic pisoliths and nodules in sandy or clayey sediments. Ferruginous mottles are formed by accumulation of hematite and goethite in saprolite, residual clays or sediments. Ferruginous saprolite is formed by the uniform ferruginization of saprolite. Iron segregations form by the replacement and/or modification of sulphide-rich lithologies or as exotic accumulation of Fe oxides along preferred pathways, such as fractures, faults and lithological contacts within saprolite. Gold dispersion in the ferruginous zone of the profile is commonly considered to have a ‘mushroom’ shape formed by downward weathering, where the surficial Au halo is derived from the mineralization by a combination of chemical, residual and mechanical processes. In this study, appreciation of regolith–landform history provides an understanding of the nature of Au dispersion (or lack of it) in ferruginous materials. It has been possible to relate the mechanisms of dispersion of Au to the material being ferruginized, the environment of ferruginization and its position within a weathering profile. The distribution of Au at the micro-morphological scale provides evidence of a mobility related to the formation of particular facies of ferruginous duricrust. Accordingly, it is essential that careful attention is paid to characterization of potential ferruginous sample media and their location in the landscape in order to deduce their relationship to bedrock.