Bowdens Silver Project Rapid Mapping of Ore Hardness in 3D Case Study

“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.”

MashIt

Project Overview

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. 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. This leveraged off existing resource drill hole data, saving time and money.

The challenge

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 result

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.

Our approach

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.

Our approach

AMC’s approach to assessing the optimal combination of open-pit and underground mining at San Sebastian focused on:

Constant client collaboration.
Geotechnical analysis and recommendation of pit slope angles, crown pillar requirements, and underground stope dimensions.
Mining method options assessment based on AMC’s country-specific experience.
Pit and stope optimizations.
Determination of optimal open pit / underground interface and development sequence to sustain continuous production.
Practical mine design, sequencing, and detailed mine schedules.
Cost