The geological unit called Charentes basin is composed of Eocene and Oligocene deposits, laid above karstic limestone formations of the Campagnien, in the North of the The kaolin clays of Charentes belong to this mainly continental, tertiary formation often referred as “siderolithic”, of which the principal outcrop is situated in the South of the Charente Maritime department, going North-East from city.
The present exploitation of kaolin clays in the Charentes basin, is based on the processing of sampling, examination of the grades in Al2O3, organic material, and a few chemical elements. The variability of the results obtained after the industrial process allows us to consider ways of improvements.
The complexity of the geological setting due to the presence of different geological processes which can produce a mixture of statistical populations in space and in the time scales is one the main difficulties of the utilization of geostatistical estimation tools.
Post-sedimentation processes have disturbed the general sedimentary relation between data, so the geological phenomena related to this processes must be taken into account for estimation. They can be used as a guide to divide the deposits into the more geologically homogeneous sub-domains. Sedimentary forms are very important for the calculation of the variograms and as a guide to link data during kriging.

Project Partners:

Research Center of Geotechnics and Underground Exploitation (CGES)- Paris School of Mines 

Publication and Repports:

Résumé:

La genèse des gisements de kaolin du Bassin des Charentes obéit à des règles géologiques simples mais leur géométrie détaillée présente une grande complexité, renforcée par le fait qu'on doit distinguer des argiles de qualités très différentes. Des méthodes géostatistiques sont proposées pour l'étude de ces gisements et sont appliquées à l'un d'eux. Une évaluation globale de la ressource est obtenue en travaillant sur la puissance totale des passées d'argile exploitable et sur l'accumulation verticale des différents constituants. Une évaluation par bancs est obtenue de façon similaire, en définissant une puissance partielle et des accumulations partielles relatives à chaque banc. Des simulations géostatistiques permettent de visualiser la variabilité spatiale des différentes catégories d'argile. Elles ont été mises en œuvre dans le cadre de la méthode des plurigaussiennes seuillées. Deux cas ont été traités: simulation de faciès argileux fondés principalement sur des critères visuels, et simulation de classes d'argile définies à partir de leur teneur en Al2O3.

Abstract:

The present exploitation of kaolin clays in the Charentes basin, France, is based on the processing of sampling, examination of the grades in Al2O3, organic material, and a few chemical elements. The variability of the results obtained after the industrial process allows us to consider ways of improvements. We present the results of a study aiming at the integration of the spatial distribution of grades and mineral characteristics, the geometry of the retaining structures and the secondary phenomena of weathering – erosion, affecting the deposit. This study is based on a principal components statistical analysis, deposit by deposit. A variographic study is then performed on each relevant variable, on re-assembled populations. Together with this statistical study, a comparison with the field observations, allows us to plan and use the sedimentation process models, taking into account deposition energy. The result of this study should be worth using for the exploitation, together for the simulation of reserves and the control of clay quality. The objective is to allow the better mastery of the expected/performed couple and the better scheduling of the exploitation.