A comparative study of lignite resource estimation based on 1D drill-hole mineable lignite compositing of uncorrelated seams and 3D mineable lignite aggregation of correlated seams

Abstract

The majority of lignite deposits in Greece consist of multiple thin lignite layers and are traditionally estimated using a one-dimensional compositing approach that can potentially lead to large errors, particularly in the presence of medium to severe tectonic disturbance and uneven vertical distribution of the seams. Drill-holes are evaluated using mining and processing criteria leading to a number of mineable lignite 'packages' along each hole, the sum of which is reported as the total mineable lignite at each drillhole horizontal location. The total mineable lignite thickness values from the various drill-holes and associated weighted average qualities are interpolated horizontally, leading to a two-dimensional model of mineable lignite. A more advanced version of this one-dimensional approach has been applied in the past, with improved results. In this version, the one-dimensional approach was limited to a single mine bench and repeated separately for each bench, thus reducing the scale of potential errors and better approaching the vertical distribution of mineable lignite. Lignite deposits, such as the one examined in this paper, require the development of a thorough stratigraphic model to allow the reporting of accurate lignite resources and to form a solid basis for mine planning and the calculation of lignite reserves. The evaluation of mineable lignite using mining and processing criteria can then be applied to correlated and modelled lignite seams, leading to an overall three-dimensional model of the deposit that allows accurate calculation of lignite resources even in the presence of deformation. This paper presents all three modelling approaches through a case study based on part of a real lignite deposit. The effects of using each of the approaches are analysed and the benefits of the three-dimensional approach are clearly demonstrated.