Optimisation of Mining Block Size for Narrow Tabular Gold Deposits

Abstract

The geological block model is used as the basis for the grade-tonnage curves and subsequent financial models. On some narrow tabular gold deposits, these blocks are observed to be significantly smaller than the smallest block that can be selectively mined. The effect of this on the financial model is not clear. This paper explores how differences in the mining block sizes affect the financial model. Monte Carlo simulation is used to create a series of hypothetical, narrow tabular gold deposit databases with a range of average grades at either side of the assumed cut-off grade. EXCEL, as well as Leapfrog Geo, software is utilised to create geological block models with a range of sizes. Grade-tonnage curves are created for each model and the assumed cut-off grade is applied to determine the resultant tonnes and average mining grade above cut-off grade. Financial models created by these are compared to determine how critical it is to have the mining block model dimensions similar to the smallest selective mining unit. It is shown that there has to be a broad similarity in the dimensions of the blocks used for planning purposes and publishing grade-tonnage curves and financial projections when considering the EXCEL model. This trend is, however, not observed when considering the grade-tonnage curves created from the Leapfrog Geo generated model. This model is considered to be a more reliable approximation of how grades are extrapolated into blocks and show how the theoretical EXCEL generated model has a higher resolution than is realistically possible when considering sample spacing. The financial outlook for the hypothetical mines can also be altered by changing the mining method to change the selectivity of the ore body.