Ninth International Geostatistics Congress, Oslo, Norway
June 11 – 15, 2012



Abstract No.:



The Effect of Considering Density as Weighting Factor When Compositing Assay Grades and as Accumulated Variable on Mining Reconciliation


Paulo Mauricio Dias, Federal University of Rio Grande do Sul (BR)
J F C L Costa, Federal University of Rio Grande do Sul (BR)
C Diedrich, Vale S.A, South Atlantic Operational Copper Department (BR)
V Koppe, Federal University of Rio Grande do Sul (BR)


The decision about where a mined material should be sent is constantly risen during short term mining planning. These decisions are mainly based on a grade model, costs, and on the quantity of material required to be mined. Therefore, an effort is spent to apply the most appropriate techniques to obtain precise and accurate estimates avoiding misclassifications of a mined material. One among various causes influencing misclassification can be related to mistakes made when estimating a block. Density should be used when compositing grades as a weighting factor otherwise can lead to possible problems on the estimates. Various studies confirmed the impact on the estimates when density is not considered when compositing. Even though the importance of considering density as a weighting factor is proved, the impact on the decision making during the mining operation of the two estimated models generated by these two ways of compositing was not analyzed yet and the possible consequence was not covered in terms of short term mining decisions. This study reports the impacts of disregarding density as a weighting factor when compositing and the downstream consequences of sending a mined material to the mill or to the dump pile. The impact was analyzed in terms of a possible misclassification of these mined materials given the two estimate models: one considering density and core lengths as a weighting factor and the other disregarding the density and compositing grades taking into account only the core lengths. For these two estimates three contact dilutions were considered and the result compared against the mined grades. Comparing these two estimates with the estimates obtained by blast hole samples it was shown that the estimates that used density as a weighting factor match better with those obtained by core samples. Additionally, the estimates using samples compositing only by sample core lengths lead in a misclassification of the mined material. In this case, disregarding the density as a weighting factor changed the destination of the mined material based on the long term mine planning estimates. This kind of misclassification does not occur when the density is used for properly weighting. Thus considering not only core lengths as weighting factor but density too lead to a more accurate process to obtain more precise estimates.




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