AMC’s field trial and multivariate analysis established predictive relationships that enabled the results of 14 SAG mill comminution (SMC) tests to be extrapolated, using 12,529 sample assays from previous core and reverse circulation drill holes. Leveraging off existing resource drill hole data, saved time and money.
Highly variable ore hardness presented a challenge for process plant design, mine scheduling and operations. A programme of conventional comminution testing to map ore hardness in 3D would be expensive, slow, and would require a vast amount of new core drill holes. What could be done with the existing core and reverse circulation drill hole data?
Forecasting the hardness of the ore and correctly scheduling the mining sequence will be important for comminution circuit design and for meeting throughput targets. The results of the conventional comminution tests indicated a wide range from soft to very hard ore, even within the same rock type.
The Bowdens silver-lead-zinc deposit is dominated by welded tuffs, rhyolites, volcanic breccias, and basement-derived conglomerates. As part of feasibility studies, conventional metallurgical testwork was carried out using drill core samples. The testwork included a selection of 14 half core samples of approximately 30 kg for comminution testing.
The tests demonstrated that the Equotip can be used to map hardness variations in drill core at a scale that can be correlated to comminution test data and geological observations. At a cost of a few dollars per metre, the Equotip survey was much less expensive than conventional comminution testing. Systematic logging of all the drill core from the deposit with an Equotip is, therefore, a cost-effective option. The ability to map hardness in 3D provides a basis for much better estimates of power consumption, mill throughput, and operating costs for the Bowdens project.
As part of a geometallurgical programme to characterize the ore, AMC conducted an orientation survey using an Equotip impact hardness tester, using both old and new drill core. The programme also included multi-element geochemical analysis. The hardness measurements showed remarkably strong correlations with Bond ball work index (BBWi) and the A x b parameter used for SAG mill circuit design. The hardness values also showed a positive correlation with potassium and sodium in all rock types. This is strongly suggestive of a relationship between hardness and hydrothermal alteration of the volcanic rocks.
Company: Silver Mines Limited
Operation: Bowdens Silver Project
Location: New South Wales, Australia