Mineral deposits are heterogeneous. The common response is to attempt to smooth or blend the feed to downstream processing. This smoothing process often starts early in data collection, so even mine block models don’t capture the full heterogeneity of the orebody. While smoothing makes sense once a flowsheet is settled, perversely it has also hindered the adoption of manufacturing principles in the design of new flowsheets.
Grade Engineering Methodology
CRC ORE has developed a toolbox of analytics and techniques (i.e. Grade Engineering) to assess the potential to apply coarse upgrading to any ore. A range of possible separation techniques can be assessed, and the response of that ore ranked relative to other orebodies.
This approach has been developed and validated in over 27 site-based studies across 7 countries. On some sites, the heterogeneity does not support a business case; on other sites a very significant business case has emerged. The increasing database of industry studies means faster and more accurate desktop assessment for new operations.
Five potential coarse separation mechanisms are:
Any orebody may respond to one or more (or none) of these levers, and they may combine to increase effect. For example, induced size deportment does not rely on natural size deportment but may be enhanced by it. Induced size by differential blasting will also increase mill throughput because of the finer mill feed. The most appropriate mechanism(s) will be determined by the characteristics of the mineralisation and the heterogeneity of the deposit.
Dense medium separation or natural size deportment will not suit disseminated mineralisation. Yet the orebody may exhibit significant variation in grade across the production bench. This could be exploited by grade sensing in belt or bucket and diverting low grade intervals to waste. Alternatively, differential blasting can induce a size difference between high grade and low grade zones in the pit, with the low grade coarse fraction removed by screening.
CRC ORE has tested a wide range of ores and has developed protocols to place an ore on response ranking curves to assess coarse separation potential relative to other ores.
The only objective of development work is to demonstrate and deliver improvements on operating sites. CRC ORE works closely with partner sites to achieve this. One site demonstration is depicted in Figure 2. The production benches in this operation exhibit significant variation in grade. This was exploited by differential blasting, and then run-of-mine rock was screened on a grizzly with undersize sent to the mill and oversize stockpiled.
The trial was remarkably effective. Mill feed grade increased by over 100 per cent above originally planned feed grade for the duration of the trial. The rejected (stockpiled) material was below-cut-off- grade material, so it is appropriate that it was excluded from mill feed. However in the short term this reduces metal feed to the mill, until mining plans are adjusted to replace the diverted metal. This can be done by repeating the differential blasting technique on waste benches to recover pockets of high grade that would otherwise be lost. Thus metal production rate can be maintained or increased with a higher mill feed grade. Economic streams can be generated from previously sub-marginal ore. This is a step change in productivity using simple technology - blasting, belt sensing, diverters and screening. The technology components are available, but first the business case for various options must be assessed, conponents must be assembled and engineered into a robust solution. These are the objectives or CRC ORE.