3&4D Geomodeling Applied to Mineral Exploration J.J. Royer, P. Mejia, G. Caumon, and P. Collon-Drouaillet Université de Lorraine, CNRS-ENSG, Vandoeuvre-Lès-Nancy, France - Email: royer@gocad.org Abstract. 3 & 4D geomodeling is a computer method allowing reconstitution of the deformation history of geological formations. It is common used since more than a decade as an exploration tool in oil and gas. It begins to be applied nowadays in mineral exploration. After summarizing the basic notions, concepts, and methodology of 3&4D geomodeling, we describe its application to mineral resources assessment and to the modeling of ore deposits comparing on limitations and recommendations. A 3&4D GeoModels cases studies of Kupferschiefers, Foresuedic Belt (Poland, Germany)., achieved during the EU FP7 ProMine research project illustrate the methodology. Perspectives and recommend- dations on applying 3&4 geomodeling in mineral resources appraisal are given in conclusion. Keywords. 3 & 4D geomodeling, CAD, Gocad, resto- ration, mineral resources, ore deposits, Kupferschiefer, ProMine. 1 Introduction 3 & 4D geomodeling is used as an exploration tool to better understand mineral resources appraisal, both at the mining exploitation and at the exploration stages. Several packages are available for processing datasets acquired during mining exploration and exploitation such as GIS and geomodelers (Bonham-Carter, 1994; Mallet, 2002). Among them, the most used are: the 3D Geomodeler (Geomodeler, 2012) from BRGM and Intrepid, Vulcan (Vulcan, 2012) from Maptek, MicroMine (2012), Surfer (2012), Surpac from GemCom (2012), Gocad-Skua from Paradigm (2012), Petrel from Schlumberger (2009), and Move3D from MidlandValley (2012). Only one or few specific modeling applications are treated by the above software; very few can encompass all tasks required in an integrated mining study (i.e. structural geology, geobody modeling, restoration, geophysical inversion & interpretation, geochemical analysis, resource & reserves estimation, mine planning, design and risk and environmental impact mitigation). Such a general- purpose modeling framework is nonetheless relevant as observed by McGaughey (2006), Caumon et al. (2009) and Caumon (2010). Basic geo-modeling notions and concepts do not depend on the software package used, although some aspects are more or less exposed to the user depending on the software package and its underlying technology. After a short presentation of geo- modeling to beginners, we will present examples obtained on the Gocad software platform during the EU FP7 ProMine research project on several European belts, including Fennoscandinavia (Finland, Sweden), Hellenic (Greece), Iberic (Spain, Portugal) and Foresuedic (Poland, Germany). (a) (b) Figure 1. Geological (a) and velocity (b) geo-models of the Los Angeles basin built using Gocad. This model was used to build the crust and upper mantle velocity model for predicting seismic risk (After Tape et al, 2009 and Plesch et al, 2009). Figure 2. Basic elements used to build discrete geo-objects. The Topology is the set of connections or links between nodes. 2 Introducing 3D GeoModeling Geo-modeling, a term coined in the 90’s to name computer techniques used to build 3D models (Mallet, 2002) have been extensively used in the geosciences (Fig. 1). The different basic notions involved in geomodeling will be explained in the following. 2.1 Geometrical Elements (micro-topology) The basic simple elements used in geomodeling are: • Points: locations defined by coordinates X, Y, Z. • Curves: points linked together by segments, may content several components (i.e. contours map). • Triangles: three linked points form a triangle; a set of adjacent triangles form a triangular surface (TSurf)), which may have several components. • Tetrahedron: four points linked together delineate an elementary volume called a Tetrahedron; A set of tetrahedra form an unstructured grid deliminating a volume. Such tetrahedral meshes are a classical support in the finite element method. • Rectangular prisms (or Voxels): a cube may be deformed so as to form an elementary hexahedron cell; when the cells are all identical (same sizes) and adjacent together, they delimitate a regular Cartesian Grid. Prisms may also be deformed to fit curvilinear stratigraphic formations. • Polyhedral cells: irregular cells whose juxtaposition forms unstructured grids.