Whole-of-mine optimization and geometallurgy

Geometallurgy may be defined as the integration of geological, geotechnical, mining, metallurgical, environmental, and economic information to provide a platform to increase the net present value of a deposit.

Geometallurgy provides benefits including:

• Better control of the comminution characteristics of ore, resulting in less variability of feed to the crushing circuit and greater throughput.
• Improved knowledge of valuable mineral species, leading to improved metal recovery and concentrate quality.
• Improved knowledge of value-destructive mineral species that may interfere with mineral separation such as talc, graphite, clays, etc, leading to improved metal recovery.
• Identification of opportunities for ore preconcentration and beneficiation.
  
  

Higher throughput and recovery generate higher revenue and better-controlled, more stable operations leading to lower operating costs.

Although some geometallurgical principles have been applied for many years, it is only in the last decade that geometallurgy has begun to be explicitly recognized and more widely employed. The increased attention paid to geometallurgy has been driven by the convergence of several factors, including declining grades, increasing complexity of mining projects, the rise of data analytics, and improvements in technologies for measuring chemical, mineralogical, and physical characteristics of ore.

The “geo” in geometallurgy recognizes that in mining and ore processing the behaviour of the ore at every step is controlled by the geology. Even in mechanical processes such as blasting, crushing, and grinding, the fragmentation of the ore is determined by its mineral content, grain size, texture, and structural fabric, and how these features respond to the particular stresses applied to them.

Thus, geometallurgical investigations typically seek to match a wide range of quantitative data that map the geological characteristics of the ore with quantitative data that record the response of the ore to mining and processing.

Many response characteristics of ore are estimated from proxy variables: attributes of the ore that can be measured cheaply and in large quantity and used to predict processing behaviours that were previously forecast from a very small number of expensive direct measurements. Proxy variables provide an avenue for estimation and scheduling, at a detailed scale, of characteristics such as mineral recovery, energy consumption, and reagent consumption in the process plant.

Multivariate data analysis is essential for finding meaning and establishing predictive relationships from these complex data sets. Established statistical methods for classifying ore types, such as principal components analysis, are being supplemented or replaced by machine learning, genetic algorithms, and decision trees.

The application of geometallurgy steers project teams towards the goal of building total orebody knowledge and provides an integrated framework for project development. The work of each discipline group is underpinned by a shared geological knowledge-base and a clearer sense of the common goals of the project. In a sense, geometallurgy is as much a philosophy as it is a scientific discipline.

The holistic nature of geometallurgy makes it an essential input to the optimization of mining strategy for both new projects and existing operations. It is often said that ‘grade is king’ but failure to correctly characterize and design for more mundane characteristics, such as variations in ore and gangue mineral assemblage, hardness, and abrasivity, can seriously reduce profitability and project value.

Geometallurgy provides additional data and identifies relationships that can significantly improve the results of a whole-of-mine optimization. Failure to include geometallurgy in a whole-of-mine optimization is likely to lead to sub-optimal mine plans and the difference can be significant.

Mining companies are typically faced with numerous development alternatives such as production rate, mining method, mining unit size, mine development sequence, comminution route, mineral extraction technology, saleable products, and waste storage options. There may be multiple orebodies to consider, each with its own peculiarities. These alternatives are all linked and decisions made at any stage may affect the performance of preceding and successive stages. Decisions made in isolation are unlikely to be optimal and often have unintended consequences in other parts of the business.

For example, increasing fragmentation in the mine to reduce crushing costs is not beneficial if the saving is less than the cost of increased ore loss and dilution. Both the potential saving and cost are directly related to the geometry of the ore zones and the mechanical responses of the ore.

With such an array of options, choosing the right strategy is a complex task but one with large rewards. The capacity, cost, and recovery associated with each component or option is intimately linked to the geometallurgical characteristics of the ore. Hence, comprehensive geometallurgical characterization is a prerequisite for good whole-of-mine optimization.

Orebody characteristics typically vary in space in a manner that reflects the history of host rock formation, mineralizing events, post-mineralization deformation and metamorphism, and later modification by weathering. These processes lead to complex spatial variations in the distributions of rock types, ore minerals, gangue minerals, texture, and structural fabric. These fundamental features of the rocks determine characteristics of the ore and waste and their behaviour during and after mining.

Whereas, in the past, average values may have been estimated or assumed for each ore characteristic, a well-designed and executed geometallurgical programme should be used to characterize the spatial variability of the ore. The traditional resource block model can then be expanded to include estimates of geometallurgical parameters, including crushing and grinding indices or derived throughput estimates, quantitative estimates of mineral species, and associated metal recoveries, power and reagent consumption. Manipulation in the block model allows the additional dimensions of cost, revenue and time to be fully assessed in the optimization.

The characteristics of waste blocks should also not be overlooked, as they carry significant mining and post-mining costs. Estimates of rock strength, fracturing and discontinuities allow blasting and ground support costs to be estimated with confidence. Similarly, the potential for waste rock to generate, or reduce, acid and metalliferous drainage has an important bearing on costs associated with the construction and operation of waste rock storage facilities, including haulage distances, water management and closure.

A comprehensive geometallurgical block model enables development options to be realistically scheduled using a range of commercial or bespoke software tools. The value of each option can be estimated taking full account of the variability of the orebody (or orebodies) and alternative sequences of delivery of ore blocks to the process plant.

The shift away from relying on average behaviours and assumptions significantly reduces the risk of erroneous outcomes from the optimization process and thereby improves decision-making. Quantitative knowledge of the uncertainty of the estimates of geometallurgical parameters also provides the potential to apply simulation methods to more thoroughly evaluate risk and opportunity.

Decisions about the development strategy for mining projects have far-reaching consequences. Poor strategy may lead to massive destruction of shareholder value in scenarios that expose high-risk aspects of the development plan. Conversely, good strategic decisions provide strong returns and minimize risk even in adverse circumstances.

Strategic optimization should be based on solid foundations; clear understanding of the relationships between all parts of the proposed operation, realistic estimates of costs, practical experience, exploration of business risks, and good data rather than assumptions.

Geometallurgy provides critical data needed for robust analysis of strategic options. Its application also fosters an integrated approach by management and technical teams which reduces the risk of technical siloing between traditional discipline areas of geology, mining engineering and metallurgy. Geometallurgy is a cornerstone of good whole-of-mine optimization.