The impact of applying high grade domaining as a method of dealing with Gold outliers in Otjikoto mine grade control modelling system, Namibia
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Date
2020
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University of Namibia
Abstract
B2Gold Otjikoto open pit mine is located in the Northern Zone of the Pan African Neoproterozoic Damara Orogenic Belt. The ore is open ended at depth and the mine is considering underground mining in the near future. The orebody depicts gold grade zonation, with the highest grades hosted in the cores of the ore shoots within the shorter limbs and hinges of the intrafolial folds in distinctive en-enchelon veins, whilst the lower grades make up the peripherals of the ore shoots. Approximately 70% of the total gold reserve in the deposit appears as free gold. Nugget effect is the variability seen between samples that are closely spaced. The orebody variogram modeling shows a high nugget effect of 0.64, and a longest range of 74 m in the 200˚ direction at 15˚ plunge. The grade control geologists are therefore dealing with high risk of resource overestimation due to the high nugget effect. The 200˚ direction is also the direction of high continuity, which represents the plunging direction of the orebody. The High Grade Capping (HGC) method currently used during grade control resource modelling at B2Gold Otjikoto mine is associated with undue reduction in the estimated grades. Grade reconciliation at B2Gold Otjikoto mine, has consistently shown a grade underestimation by the Grade Control model against the plant processed feed grade. Therefore, the study evaluated the impact of employing High Grade Domaining (HGD) method at the mine. Two ordinary kriging grade block models were populated using both methods. The results were evaluated to quantify the impact of the two methods on the grade estimates. The result shows a 3% increase in the overall grade of the HGD model ore material compared to the HGC model ore material. Both models estimated similar grade and tonnage in ore material from lower grade zones, howerver, significant variations in the grades and tonnage occurs between the models in ore material in the in grade categories above 4.5 g/t Au cutoff. The study recommends employing the HGD method in resource modelling for mining in the high grade zones.
Description
A mini thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science (Applied Geology)