Author(s): |
C, Badenhorst, BHP Billiton (AU)
M.E. Rossi, GeoSystems International, Inc (US)
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Abstract: |
The change of support and information effect concepts are fundamental in every resource model. It underpins all aspects of resource estimation in every deposit worldwide, yet is poorly understood, rarely taught, and even more rarely applied. This paper describes the practical implications of these concepts using conditional simulation, by deriving a recoverable resource estimate for the first few push-backs for the proposed Olympic Dam open cut mine. The Olympic Dam deposit is one the world?s largest polymetallic resources at 9bt tonnes grading 0.8% Cu, 270ppm U3O8, 0.32g/t Au and 1.5g/t Ag. BHP Billion is currently undertaking a feasibility study of a large open cut operation with an estimated mine life of 120 years. The resource estimation practices at Olympic Dam comprise of a combination of linear and non-linear techniques to estimate 16 different grade variables critical to the resource. In the southern portion of the deposit, at the site of the proposed open cut, the current resource estimate data spacing is insufficient to predict the recoverable tonnage and grade that will be selected using closely spaced grade control blast holes once mining commences. Conditional simulation has been used to generate a recoverable resource estimate by measuring the tonnage and grade uplift resulting from the change of support and the information effect that occurs at the time of mining. Ten realisations of Cu, S, U3O8 and Au were generated using Sequential Indicator Simulation. The simulations were validated visually and statistically, and a single realisation was then chosen to represent ?reality?. Several ?grade control? databases were constructed by sampling the realisation at the expected blast hole spacing . Each database was used to estimate the first few push-backs of the proposed open cut mimicking future grade control estimates. Variations were measured and grade tonnage curves at the smaller grade control support were compared to the larger blocks of the resource. This information has been used to optimize the predictions of expected tons and grades fed to the mill, adjusting the recoverable resource estimate to control its smoothing. This information is critical for optimal mine planning. The results and conclusions of this work unequivocally demonstrate why every resource geologist should have a deep understanding of the change of support and information effect, and how it can be applied in their resource models using conditional simulation. |
