Fig. 1 – Simulated distribution for a geochemical data base with different proportions of igneous rocks, (meta)sediments and regolith, in the case of the Northern Pilbara Craton. Note that the effect of varying the proportion of the different lithologies produce marginal modifications of the distributions, and do not resolve the differences in peak position, width and skewness between the airborne distributions and rock samples distributions. This reflects the fact that, distributions of U, and Th, in the various lithologies are, on the first order, similar. Distributions for K are not estimated as the North Pilbara database does not include regolith samples.