Characterisation of a laterite-type bauxite orebody geometry using a plurigaussian simulation approach

A typical laterite-type bauxite deposit is formed from tropically weathered mafic-ultramafic complexes. The components of the weathering profile such as bauxite and underlying ferricrete units can be discontinuous with a relatively significant lateral variability. Understanding the major process of the lateritic weathering system and local lateral variability of the orebody contacts are of utmost importance in terms of an accurate orebody volume calculation and ore recovery at the alumina refinery. The plurigaussian simulation provides a tool that is used to simulate the lithotypes present in the regolith profile, which in turn reproduces the natural contacts between the geological units. The plurigaussian simulation approach was demonstrated in a case study where the geometry of the lateritic bauxite deposit was delineated. Four lithotypes including overburden, redsoil, bauxite and ferricrete were used in the simulation. The resulting realisation indicated a good reproduction of the conditioning data both laterally and vertically. Contrary to the deterministic models, the simulated realisation represented a possible geological model without the smoothing effect

Geometrical characterization of urban fill by integrating the multi‐receiver electromagnetic induction method and electrical resistivity tomography: A case study in Poitiers, France

(IF 2.82 [2018]; Q1)International audienceA geophysical survey including electromagnetic induction (EMI) and electrical resistivity tomography (ERT) methods was applied and assessed with a 40‐trench sampling grid to delineate the geometry of an urban fill layer. Classical investigation techniques, such as excavation, offer localized information and suffer from time and budget constraints for environmental assessments. Near‐surface geophysics can provide the required spatial sampling to evaluate the coverage of anthropogenic soils in a time‐effective and quasi‐continuous manner. Fast‐acquisition and high‐spatial‐coverage EMI mapping and high‐vertical‐resolution ERT were implemented to delineate a suspicious urban fill on a 5‐ha site in a suburban region, which will host the buildings of a commercial complex. The ERT data and 40 trench excavations revealed an urban fill thickness ranging from 0.4 to 3.6 m overlying a calcareous substratum. After ERT–EMI calibration, a two‐layer model was introduced into the one‐dimensional (1‐D) inversion of the EMI data for estimating the geometry of the urban fill layer across the study site. The EMI 1‐D inversion results indicated that the predicted urban fill thicknesses were consistent with 70% of the measured values (27 out of 40 excavation sites). Resistive ground, large 3‐D structures and the heterogeneity of urban fill affected the EMI and ERT measurements and increased the difficulty of estimating its spatial distribution. In this paper, we present a measurement protocol that can guide land‐use development and be reproduced to investigate brownfield sites