Geostatistical approach to the optimization of sampling density at Goldenrae Mining Company Limited

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The decisions on mineral deposit evaluation based on geological factors can be very crucial go belong classical statistics. Thus, geostatistical approach was used to establish the optimum sampling density for the evaluation of the Kwabeng alluvial deposit based on seven different grid densities. The seven grid densities are l00m x 50m, 100m x 100m, 200m x 50m, 200m x 100m. 400m x 50m, 400m x 100m, 800m x 50m and 800m x l00m, which corresponds to 427, 219, 324, 174, 177, 97, 102 and 52 alluvial pit respectively. The geostatistical studies involved variogram modeling of the grades of the various grid densities, examining the relationship between pit results and their zone of influence, with the view of establishing the optimum number of pits required, for the evaluation. The 100 x 50m (427 pits) was used as the standard for comparison. Histogram plots of the grades for the various grid densities displayed positively skewed log-normal distribution. The probability plots yielded two-parameter lognormal distributions. Both plots indicated excesses of high or low-grade distributions. The statistical parameters of the grid density, 200m x 50m, compare very well the standard. The directional variograrns calculated on the various grid densities revealed a geometric anisotropy with the range across the deposit being the shorter than the parallel to its strike length (i.e. downstream). The variability of grades on the deposit helped in determination of ranges of influence and assisted in optimizing the sample density. The geostatistical structural analysis in conjunction with statistical parameters of the various grid densities revealed close similarity between the 200m x 50m grid and that of the standard in terms of grade distribution and thus could have been used to evaluate the Kwabeng deposit. It was thus recommended that future evaluation elsewhere on the property or the Birim Basin could he based on the 200m x 50m grid with very minimum risk.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of Master of Science degree in Mineral Exploration, 2001