2nd International Conference on: “Advances in Mineral Resources 169 Management and Environmental Geotechnology”, Hania 2006, Greece Determination of the optimum sampling density for a multi-seam lignite deposit K. Modis and G. Papantonopoulos School of Mining and Metallurgical Engineering, National Technical University of Athens Ch. Roumpos Public Power Corporation S.A. ABSTRACT According to previously established theoretical analysis and under certain conditions, a critical sampling grid can be determined for an earth- related space-distributed natural variable. Sam- pling above this critical limit adds little to the mapping results, while based on this limit the ideal process of reproducing the original phe- nomenon is theoretically defined. The objective of this paper is the application of the above the- ory to the Klidi lignite deposit in Florina, Greece, where Public Power Corporation (Greece) has conducted a sampling campaign to estimate the deposit thickness and its heating value. Data acquired for these two variables were analysed in the space domain in order to derive their respective correlation functions. The structural analysis of the deposit generated two covariance models, one for the thickness and one for the heating value, from which the critical sampling grid was identified. The con- clusion drawn is that in some parts of the de- posit the sampling grid is denser than required. Finally, an optimal sampling grid is proposed in order to gain the maximum information at the lowest cost. 1. INTRODUCTION Lignite, a type of brown coal located on earth’s higher stratigraphic layers, is of particular sig- nificance for the power-generating sector of Greece which covers about 66% of its power needs. The confirmed lignite reserves of Greece amount to 4.5 billion tonnes, out of which 3 bil- lion tonnes (67%) are economically recoverable reserves. These reserves exhibit a remarkable geographical distribution throughout Greece. The vast majority of Greek lignite deposits are located in the Northern part of Greece (West Macedonia) and specifically in the tectonic ba- sin that extends along the axis Florina- Ptolemais-Kozani–Elassona (Fig. 1). The Klidi mining field is located in the east- ern-southeastern boundary of the entire Florina mining area, 22 km east-southeast of the Florina city. It extends approximately 3 km towards the north and the south and about 1.7 km towards the west and the east (Fig. 2). The area of the planned mine, including the Klidi village, covers approx. 5 km 2 . The mining area is hilly with surface altitudes ranging be- tween +750 m and +1100 m above sea level. Figure 1: Lignite deposits of West Macedonia and Thes- saly.