Pre-concentration is increasingly being assessed in both early-stage projects and existing operations to determine whether it can add value. Pre-concentration is applied when plant material is still coarse, dry and can be conveyed—or hauled by truck. It exploits the natural heterogeneity of the orebody, provided it persists after being blasted and crushed. Rejecting waste before it reaches the mill reduces energy and water use during downstream processing, preventing a significant amount of waste from being ground and sent to tailings.
For a greenfield project, evaluating pre-concentration can be challenging due to the lack of standardised testing methods and sample top-size constraints. This is compounded by current testing practices, where metallurgical sample preparation typically involves stage-crushing down to a manageable size — eliminating the opportunity to evaluate coarse beneficiation methods. To remedy this, SRK has developed a laboratory protocol that can be performed on small masses of ½- or even ¼-core.
The laboratory test requires only 30 to 50 kg of material and measures metal deportment by size at various levels of impact breakage, simulating primary and secondary crushing. By combining this test protocol with an established comminution test, it can be integrated into existing metallurgical testwork programs with minimal disruption. The test is kept cost-effective by limiting the number of assays.
To observe how target metals occur in coarse particles, SRK uses a dual-energy, X-ray transmissive (XRT) sensor, which scans each particle to identify areas of higher atomic density. While not the only sensor technology available, it is particularly useful for characterising samples that display heterogeneous properties.
SRK provides independent evaluations of pre-concentration before committing to the cost and sample mass requirements of performance testing by manufacturers. The results characterise coarse particles in terms of preferential breakage and amenability to XRT sensor response — all from 30 to 50 kg of ½-core, including hardness testing. Because coarse liberation sizes can yield variable results, SRK recommends testing multiple samples to quantify this variability.
In addition, standardised testing like this will support project benchmarking and development of pre-concentration indices, which can be used in geometallurgical modelling.
