A geometallurgical approach
David Meadows looks at the approach and implementation of geometallurgy in the mining industry.
During the last decade, the mining industry has experienced a substantial rise in new greenfield project capital intensity, schedule overruns, slower ramp-up, loss of productivity, increase in operating cost and a gradual depletion of skilled engineers equipped with full knowledge for project design and implementation.
Some of the test programmes related to project failures have been directly coupled to the lack of basic mineralogical knowledge, ore characterisation and sampling deficiencies together with a lack of thoroughness and number of metallurgical tests required. Geometallurgy has been around for some years, although at times can still appear to be in its infancy. Best practice geometallurgy connects multi-disciplines linking geology, mining, metallurgy and downstream tailings/environmental aspects.
The early emphasis must link to the geology and mine plan sequence together with identification of the number of samples and types of samples selected. Early development requires close interaction with exploration geologists, mining engineers and process metallurgists. Sample intervals and frequency need to relate to the nature of the deposit, lithology and mine plan sequencing. 'Listen to the ore body and diligently engineer configurations’ is taken for granted but not always given enough attention.
Once the samples have been collected they must be carefully logged ready for dispatch to the desired metallurgical test laboratory. The next step involves sample preparation – this can be a potential bottleneck in the system, and access to modern, high-throughput sample preparation is vital. The laboratory selection should be carried out in relation to core competencies, level of mineralogical and metallurgical testing and geographical consideration, taking into account sample shipment. The laboratory’s chemical analysis capability must also be considered. For example, copper ore samples collected and ready for testing in North America may be sent to SGS Laboratories or Hazen Laboratories, platinum ore samples in Sub-Sahara Africa are sent to Mintek in South Africa.
In aggressively scheduled projects, sample shipment and logistics should not be underestimated and air freighting of samples may be the only means to ship the samples internationally. Laboratory test protocols should be reviewed together with the specific test equipment, for example, running the test ball mill, size, geometry and internal liner configuration for a standard Bond Ball Millwork Index.
As the test data becomes available, the interpretation of the results and key inputs into the process design requires core competencies and experts to review the comminution test work.
Several of the recent cost overruns and/or outright flow sheet failures are related to inadequate geometallurgical work including ore profiling during scoping, prefeasibility and full feasibility studies. Inadequate geometallurgy has resulted in underperforming flow sheets, incorrect mill sizing and circuit design, run-away flotation conditions and problems with tailings thickening and deposition.
Optimising operating plants
Within the past five years, greater emphasis has been placed on improving existing plant performance and increasing asset value. Examples of this include Collahuasi Mine in Chile and Cerro Verde in Peru. Improving the upfront ore characterisation and mineralogical information is vital to the success. Ore types, lithology, clay and gangue mineralogy knowledge, together with ore hardness mapping, grade and contaminant levels are all closely tied together. Daily reporting and trending of this information greatly assists plant operations. In a number of cases notable improvements in copper, gold and molybdenum have been seen with these approaches.
Many of the successfully optimised operations have achieved this by doing regular mineralogical and process plant surveys across the entire flowsheet from the comminution including blasting and fragmentation to the final tailings deposition. There is an increasing trend of greater testing being conducted at the site via mineralogical testing facilities. Other tracking techniques including down-hole measuring techniques and cross-belt analysers on the ore feed are also advancing.
Time and cost allocation
The early upfront planning of activities in the various study and project implementation phases is a critical consideration. The budget allocation and duration of the geometallurgical programmes must be approached in a logical and realistic timeframe. For smaller projects of less than 5,000 tonnes per day, expenditure for mineralogical and metallurgical testing can be around US$1–2 million, whereas large 100,000 tonnes per day projects can cost several million USDs.
The time frames of testwork for larger projects can go from 6–18 months depending on the extent of work. Often there will be overlaps with the testing and the various forms of scoping, prefeasibility and feasibility studies. Shortcuts and cost cutting on the test work programme can rapidly backfire, resulting in prolonged plant start-up and inability of the plant to consistently make the nameplate capacity.
During the last decade the level of interest in geometallurgy has continued to grow. For example, Dassault Systèmes, France, who specialise in 3D design, 3D digital mock-up and product lifecycle management software, using the GEOVIA SurpacTM software system to support its open pit and underground mining operations and exploration projects. The new software is used at mine sites by engineers, geologists and mine surveyors and combines data management, modelling and planning to enable mining practitioners to quantify and evaluate mineral deposits and plan the efficient extraction of reserves. Geologists can determine the physical characteristics of a deposit with 3D graphics, geostatistics and an integrated modelling environment. DJB Consultants, Canada, has also actively participated and guided the development of a number of successful geometallurgical programmes including Los Pelambres Mine in Chile, Batu Hijau in Indonesia and Troilus in Canada.
As practicing metallurgists in geometallurgy, it is important to share the experiences and requirements within mining company organisations and outside institutions. The impact and benefits should be shared from lower ranks of the organisation all the way through to CEO level. The direct impact stemming from the appliance of a solid geometallurgical programme will often be reflected in a fast uneventful plant ramp-up, with the plant achieving its metallurgical product targets within six-to-nine months of first plant feed. To the outside financial institutions and bankers, these positive impacts do a lot for the industry and future growth in more challenging metal price times.
The goal is to provide flow sheet design that is sufficiently tailored to the specific ore and its variability while seeking process simplicity and appropriate use of standard equipment. A strong geometallurgy programme will increase the net present value by providing an optimal flow sheet that avoids process inefficiencies and expensive troubleshooting.
David Gilbert Meadows FIMMM is Global Manager of metallurgy at Bechtel Mining and Metals with more than 31 years of international experience in the minerals industry, specifically in the field of minerals processing engineering. He has participated in all phases of projects from early geometallurgy/process test work to final commissioning and plant optimisation.