While ore sorting is not a new concept, technological developments in recent years combined with declining head grades have refocused the industry on its effectiveness in a wider range of applications.
Determining the applicability of sorting starts with analysis of the ore body heterogeneity. If sufficiently heterogeneous, sorting can start with grade delineation in the mine. From there, sorting can mean anything from separation based on size fraction (natural upgrading), bulk sensor based sorting by on conveyor stream analysis, to individual particle sorting based on colour, radiometric characteristics or other detectable factors. As a result, the limits of ore sorting are determined by the speed we can detect, the detection limits, the speed we can process the information and the ability to efficiently separate ore from waste.
Broadly, there are three cases for improving project value through ore sorting:
Converting sub grade waste (including previously rejected material) to ore that can be economic at modest recovery of values
Sorting of ore to increase grade and reduce subsequent processing and transport costs
Sorting of ore to bring forward cash flow
The first case adds value to the project by conversion of waste to ore. On this basis, recovery is not critical and the value of the recovered material needs to cover processing costs plus margin. This can add significant value to a project where the processing capacity exceeds the ore supply rate and mine waste can be converted to “ore” by simple low cost processing.
The second case is generally only economically favourable if the processing and ore transport costs are high (in relation to the head grade) and the recovery of values is also high (e.g. >95%) . This is particularly applicable to massive ore bodies where there is little disseminated material but a component of the ore that is waste and has not been able to be separated in the mining process.
The third case requires that the treatment of the rejected material is deferred in the processing schedule such that cash flow and NPV is increased. This requires that the cost of mining, sorting and ore storage is low and implemented without major capital and operating cost impacts. This scenario has challenged many projects that aspire to use Grade Engineering™ or similar concepts.
We are currently involved in projects for each of the above scenarios. Contact Greg Lane or Paul Staples for further information on how we can analyze your project and assess the value of implementing ore sorting.