Geometallurgy: new methodology to measure ore hardness variability for production forecasting

IMPC 2014


The main purpose of geometallurgy is to improve the mine planning by mapping hardness and throughput into the mine block model using geostatistics to eliminate the large production fluctuations caused by the ore hardness variability coming from different parts of the pit. However, not all grinding testwork available commercially can be applied to geometallurgy because of large amount of sample required and the associated cost per test. Also, as projects progress, the accuracy of engineering must improve from 30-35% during the scoping study to 10-15% at the bankable feasibility stage.

For SAG milling, the SAG Variability Test (SVT) is an abbreviated version of the standard SAGDesign test developed for this geometallurgical need. The ore is ground for three cycles and then predicted to the standard end point of 80% passing 1.7 mm. For ball milling, a Bond Variability Test (BVT) was also developed using the SAG ground ore from the SVT. The average of the net grams per revolution from the last Bond cycles is also predicted from the third cycle. The relative error for both the predicted SAG ore hardness and Bond Work Index (BWI), in kWh/t, averaged 5.5% and 3.8% respectively compared to the SAGDesign testwork values. Both tests can be continued to measure the true hardness necessary for mill sizing.

In addition, the SVT was performed on individual samples and composites made of those same samples. The SAG pinion energy of the composite samples were within 4.5% of the weighted average of each individual samples values, representing ore blending. The number of geometallurgical samples can be reduced significantly if chosen carefully. This article discusses the development and results of these two new tests, SVT and BVT, and their potential use in any geometallurgical program.

This was presented at  2014 SME. The full paper will be published in the proceeding of IMPC 2014.