April 2015

A step change in mining productivity

  • By Joe Pease, CEO; Dr Stephen Walters, Research Director; Melissa Raassina, Communications and Education Officer; Dr Luke Keeney, Technical Manager; and Greg Shapland, Implementation Specialist; CRC ORE

Time to deliver the promise

The mining industry has long sought a step change in productivity through the integration of operations from mine to market. There have been some success stories, but in general, the promise has not been delivered. CRC ORE and its industry participants believe the time has arrived to change that. Crucial gaps in technology and systems that hindered integration have now been addressed. At a time when the industry desperately seeks productivity change, we now have the tools to finally deliver the promised benefits of integration.

The mining productivity challenge

The minerals industry is facing a productivity and investment crisis. The ‘Millennium Super Cycle’ from 2003-11 was an unprecedented period of growth and investment, seeing throughput increased and lower grade resources developed to meet demand. The urgency to bring production to market quickly stretched people, project and management resources. Now prices have declined and the industry is left with the legacy of high costs, declining ore quality and less efficient operating practices. For example, the average grade of copper ore mined in 2020 will be half what it was in 1990. Along with other growing challenges (stripping ratio, site logistics, mineralogical complexity), it will take more than twice the activity to produce each tonne of metal. Meanwhile, it has been well reported that productivity in Australian mining has already dropped by over 40 per cent in the last five years. So there is an urgent need to make significant productivity improvements without major capital investment.

The ‘Millennium Super Cycle’ from 2003-11 was an unprecedented period of growth and investment.

The Cooperative Research Centre for Optimising Resource Extraction (CRC ORE) believes this is achievable. They are working with the global resources industry to reverse the trend of declining feed grade and quality through novel approaches and innovative solutions.

Transforming mining productivity – an integrated approach

CRC ORE was established in 2010 to address productivity challenges. It is a large scale, industry-led initiative that brings together orebody knowledge, mass mining, mineral processing and resource economics. CRC ORE provides a bridge between technology development and site implementation, through collaborations with a consortium of global mining companies, mining equipment, technology and services (METS) providers and research organisations. The aim of these partnerships is to achieve a step change in productivity by adopting an integrated, manufacturing-style approach to the production of metals from drill core to product. Particularly, there is a focus on improving feed quality early in the production value chain.

The minerals industry has long sought to improve productivity by integrating operations from mine to metal. In the 1990s this was the driving force behind ‘Mine to Mill’. The disappointing thing was not that Mine to Mill failed to deliver value, but that it did so successfully and yet then withered. It was widely accepted, but not widely adopted. Even worse, many of the successful ‘poster’ sites gradually reverted to the traditional silo approach of managing operations.

CRC ORE has worked to understand why those good intentions failed to deliver or be sustained. It was not because industry didn’t try, but rather, because crucial gaps in technology and systems meant solutions were not robust enough to survive the operating environment. CRC ORE seeks to close those gaps to enable robust, long term, integrated systems for minerals production.

Closing the gaps

CRC ORE is focused on addressing the key barriers of measurement, ore heterogeneity, integrated systems, and supporting management systems. The first phase of CRC ORE worked to identify and develop solutions in the first three areas. The next phase will focus on combining and implementing these new tools to deliver outcomes on operating sites. In parallel, management and organisation systems will be developed to support and lock in the changes.

Measurements

A manufacturing plant controls its feed within strict limits, setting specifications and measuring to ensure compliance. In contrast, feed quality in mining is variable. In most cases, we can not measure quality as it enters the production process. We can measure and control over 200 variables on a haul truck. We can operate it autonomously from the other side of the world. We have almost no measure, however, of the most important aspects – the quality of the payload, the feed to the metal manufacturing.

Providing routine on-line feed quality measurements of coarse run-of-mine (ROM) ores or mill feed is technically challenging. However, ongoing developments in sensor technologies in fields such as Neutron Activation, Magnetic Resonance and Laser Induced Breakdown Spectroscopy offer potential solutions. In some cases, these technologies are already being used at feed belt scale in rock-based industries where maintaining feed quality specification is crucial to generating saleable product, eg cement manufacture. The next step is to prove their application and business value for bulk base and precious metal mining. Measurement of grade early in production opens new fields of possibility for coarse separation.

A medium term vision is to sense the grade in every loader bucket or transfer point, to enable a separation decision at multiple points. This requires the development of more robust and compact measurement hardware. However, the technology already exists to measure grade on conveyors. This could identify intervals of high grade or low grade ore that could be diverted to separate destinations. This will enable some important applications of Grade Engineering®. An ultimate manifestation would be an In-Pit Conveying and Separating system (ICPS) as shown in Figure 1, yet there are many less ambitious options that can be applied now.

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Heterogeneity – friend or foe?

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.

CRC ORE believes that a manufacturing approach to integration must start with an acceptance of the things that fundamentally differ between mining and manufacturing – measurement difficulty and feed heterogeneity. Rather than try to eliminate heterogeneity by smoothing, the early stages of mining and processing should embrace and exploit it. This is the principle behind Grade Engineering®. It means identifying and removing low grade unprofitable materials as early as possible, whenever possible, however possible.

The concept of removing uneconomic material rather than smoothing it through plant feed is not new – it was practiced by our forebears as hand-picking; is practiced in some plants as Dense Medium Separation, and in others as Ore Sorting. In a well reported example, Bougainville Copper upgraded sub-marginal ore by screening to remove coarse low grade rocks, exploiting a natural preferential deportment of copper values to fines. The impact can be enormous – the Dense Medium Plant at Mount Isa lead zinc removes about 35 per cent of coarse and hardest feed before the fine grinding treatment process. That increases the throughput, reduces the capital intensity, and reduces energy requirement by over 40 per cent.

Yet it seems the principles of early waste removal are not always considered in the design phase of a mine. Many operations design the standard circuit of stockpile-conveyor-SAG mill-ball mills-flotation. Once selected, this circuit prefers a smoothed feed, and the materials handling and feed sizing prevents the application of most coarse separation options. This flowsheet may well be the best solution for an ore, but that can only be judged after options to exploit coarse ore heterogeneity have been examined. An interesting question is this: if your company was developing Bougainville or Mount Isa lead zinc today, would it consider a coarse screening plant or dense medium plant? Or would it just accept the higher capital, higher operating cost of the standard circuit?

Grade Engineering

Every ore is different. Different areas of the same orebody are different. Therefore, any solution must recognise that there is not a general solution, but there can be a general approach. CRC ORE has developed a toolbox of analytics and techniques (ie 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:

  • induced sized deportment by preferential blasting – eg blast higher grade zones fine and low grade zones coarse, and then separate by
    coarse screening
  • natural size deportment – ie exploit natural tendency of valuable minerals to concentrate in fines; upgrade ore by screening out coarse low grade rocks
  • coarse gravity separation – exploit coarse gangue liberation by removing it before grinding, for example dense medium, jigs
  • sensor based mass sorting – measure (or infer) grade, divert low grade batches or conveyor intervals to waste
  • sensor based particle sorting – measure distinctive characteristic of valuable or gangue, and eject individual particles.

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.

Site demonstration

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.

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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, then the components must be assembled and engineered into a robust solution. These are the objectives of CRC ORE.

The minerals industry now desperately needs to increase productivity as both feed quality and prices decline.

The next generation of mining simulation – IES

To support the integrated approach to minerals extraction, CRC ORE worked with researchers to develop a value chain simulator, known as the Integrated Extraction Simulator (IES). IES incorporates the outcomes of over 50 years of JKMRC and AMIRA research, combining existing industry standard simulation models with models from diverse research and development sources.

IES is a mining simulator that integrates all mining and mineral processing activities starting from drill and blast, through loading, hauling, stockpiling, blending, crushing, and grinding and processing. It allows multiple ore types to be considered from the block model to product. To optimise production, each unit operation must be considered not just within its own ‘silo’, but also how it interacts with other production steps. For example, IES allows operators to assess future ore sources for the effect that changes in blasting will have on grinding and how this will impact flotation. Therefore IES can be used to assess changes in the design, layout and operating steps to optimise metal production and environmental footprint. It provides a model development environment that allows the user to access or input models that suit their specific equipment.

Therefore IES is a key tool to enable effective implementation of Grade Engineering®. At the time of writing this article, it is expected that IES will be released in March 2015. Current and future extensions of the system are in progress.

Supporting management and organisation systems

CRC ORE believes the technology and techniques for a step change in industry productivity are well within reach. The next phase of the program is to assemble and demonstrate them in high value site applications.

But to achieve the value and to lock in the gains, the technology must be supported with appropriate management and control systems. The integrated approach to production must be matched with a similar management approach. Though every organisation supports this principle, often existing management and reward systems inadvertently hinder it. Careful design of KPIs, targets and incentives is required to ensure that individual efforts combine to optimise the overall site, and not isolate activities into silos. For example, the drill and blast crew should be rewarded (not penalised) for increasing their unit cost if it increases site productivity. This principle is well understood, yet KPIs remain insidious barriers to genuine integration. CRC ORE works with business management leaders, senior industry leaders, and system providers to develop the tools and business support for integrated operations.

The time is right

The Mine to Mill initiatives of the 1990s showed that better coordination of activities will yield significant productivity gains. Yet the changes were not robust enough to be maintained.

After an era of major expansion to meet the Super Cycle, the minerals industry now desperately needs to increase productivity as both feed quality and prices decline.

The tools, both technical and analytical, are now much better developed. They can now be combined to quickly assess ores and options, and in many cases to demonstrate significant improvement. The technology is simple. Further engineering and site demonstration is needed to make it robust and reliable. Then it needs to be supported with appropriate organisation and management systems.

Finally, the time has arrived and the tools are within reach to truly integrate mining operations. 

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