A geostatistical modelling approach to gold mineralisation at Hutti mine, Raichur District, Karnataka

Hutti gold mine, located in the Archaean Hutti-Maski greenstone belt, is one of the major gold producing mines in India. Gold mineralisation is associated with parallel to sub-parallel, steeply dipping auriferous quartz veins localised in a major shear zone in the western segment of the greenstone belt. Coarse and fine grained vesicular metabasalts of Buddinne Formation are the host for auriferous lodes reflecting a litho-stratigraphic control. The present study deals with geostatistical modelling for Hutti gold mineralisation, keeping in view the various controls of mineralisation and geological setting. The geostatistical modelling carried out for gold accumulation and width of mineralisation from underground drives and cross-cuts at 18(th), 19(th) and 20(th) levels of Strike Reef reveal a positively skewed 2-parameter lognormal distribution fit. Semi-variogram modelling for gold accumulation reveal a high nugget effect and a moderate continuity with a small range of influence and that for width, a moderate to high nugget effect and a moderate continuity with a small range of influence. These spatial parameters reflect the erratic nature of gold mineralisation. Block value estimation has been carried out employing 3-D kriging technique. The results of block kriging have been used to compute an ore inventory for the three levels and to establish grade-tonnage relationships estimating the (i) quantity of ore, gold metal and waste; (ii),average grade of ore above a series of alternative cutoff grades; (iii) waste-to-ore ratio following a step-wise integration of the block grade frequency distribution over a range of grades. These estimates then form a sound foundation for mine decisions.