USE OF CONDITIONAL SIMULATION FOR RECOVEREBLE RESERVES EVALUATION OF A POLYMETALLIC OREBODY IN ALBANIA

This paper describes the preliminary procedure for recoverable reserves evaluation that was applied to Munella orebody (Albania) which is characterised by high dispersion and spatial irregularity of useful metals: copper, zinc, gold and silver. The orebody had been explored by means of 230 subvertical drillings of about 250-300m length. Deviations of the drillholes from the design orientation had been measured at intervals of 25m along 80% of the drillholes. 1) The first step of the task consisted in reconstructing the position of the drillholes for the remaining 20% of the drillings, by means of geostatistical estimation of the unit variations of direction and inclination. 2) The second step was a study of the spatial distribution and of correlation between grades and the characteristics of the mineralisation. A complete variography was carried out. The application of Discriminant Analysis showed that the type of existing mineralisation could be linked to ore grade, allowing to classify all the samples under the four mineralisation classes identified by the petrographic study. 3) The third step consisted in the conditional co-simulation of the grades of the useful minerals for a tentative characterisation of reserves based exclusively on successive selections on each variable simulated. The result of the preliminary evaluation study was the evidence of the need for a more sophisticated parametrisation of the recoverable reserves that expresses the different degrees of recovery of the orebody depending on the different mineralisation facies and on the alternative mining hypotheses that can be envisaged. The entire procedure identified is the object of ongoing research work.