Getting the Geo into Geomet Karin O. Hoal (SEG 1998 F) Director, Advanced Mineralogy Research Center and Research Professor, Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado USA 80401; e-mail,
[email protected]
INTRODUCTION
characterization and geometallurgy into their academic programs. Of note are the universities of Johannesburg and Cape Town in South Africa, Western Australia and Tasmania in Australia, McGill in Canada, Universidad Católica in Chile, and Colorado School of Mines (CSM) in the United States. At CSM, mineral characterization forms a part of the Advanced Mineralogy Research Center (Fig. 1) and related courses. This This newsletter contribution relates our recent experiences incorporating geometallurgy into resource extraction discussions. While mining forms a key part of our activities, research in oil and
gas, environmental, health, and planetary areas also provide insights of benefit to mining projects.
A consensus has developed in recent years that the integration of geology with extractive processing aids in process optimization and improves project efficiencies. The term “geometallurgy” DEFINING GEOMET has been re-introduced to describe a At CSM, students from geology, metalgeology-metallurgy data stream. lurgy, mineral economics, and mining Geometallurgy has been variably participated in an interdepartmental defined and it has become a predomigeomet course that began with nantly metallurgical term of late. This overviews of geology, mineralogy, minis because metallurgists, acknowledging ing, mineral processing, and metallurgy that rock and mineral relationships are to establish commonalities of language important to process flowsheets, now and thought, the absence incorporate inspection of drill core into to page 11 . . . of which was an initial a geomet-determined predictive metallurgy model. In so doing, however, the wealth of geologic and mineralogical information generated early in a project is commonly ignored. Geometallurgy can instead be viewed as an integrated method to develop the geologic framework of a project, transfer that information in processing terms, and maintain a geologic presence throughout the life of a project. A number of educational instiFIGURE 1. Geometallurgy research and classes are being developed at a number of institutions tutions around the world are and are a key part of the Advanced Mineralogy Research Research Center at Colorado School of Mines. beginning to incorporate mineral
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major hurdle. Industry involvement and case studies were critical to the success of the class, and students conducted geomet research projects ranging from uranium to gold, industrial minerals, and zinc. Students from the various disciplines all agreed the central focal point of geomet should be materials characterization conducted in a language that diverse groups could understand: descriptive geologic and mineral study at the front end of a project should be transferable downstream to processing and mining departments. The students likened resource extraction to geology in reverse, that is, the geologic knowledge of formation of a particular ore deposit (temperature, pressure, alteration, fluids, acids, structures, emplacement conditions, spatial relationships) can be useful to metallurgists and miners to liberate ore more effectively. This idea is similar to Steve Enders’ concept of geomimicry (Stephen Enders, pers. commun., 2008), utilizing the geologic principles in nature in new and beneficial ways. The term “geometallurgy” was not viewed as particularly representative of the integrated nature of resources development, and students offered new terms for this field such as geollurgy, geometminops, or simply geomet, as adopted herein. Geomet is the science of integrating geology and mineralogy with resource processing and extraction. The Society’s own journal, Economic Geology, had geomet roots a century ago through expanding the geologic skill sets of processing engineers (Irving, 1906, Fig. 2). The 1950s and 1960s saw increased integration and cross-training among the mining disciplines, setting the stage for the interdepartmental and cooperative project development that flourished in the 1960s and 1970s, when concepts such as metallurgical core logging (Hazen Research, 1960s) were introduced. The term “geo-metallurgy” was likely coined by McQuiston and Bechaud (1968, p. 103) in a discussion of sampling virgin deposits: “…geo-metallurgy…since geology is inextricably interwoven with metallurgy in gaining an understanding of the complexities of a deposit, eventually leading to a definition of mineable reserves, with the development of a flowsheet and engineering criteria for the planning of a successful and profitable operation.” With increasing specialization in the fields of economic geology and metallurgy in the intervening
“…to the metallurgist and mining engineer, a full and complete grasp of economic geology in all its relations is a sine-qua-non of practical success…” Irving, 1906, Economic Geology Vol. 1, No. 1 FIGURE 2. One hundred years ago, economic geology and mineralogy were critical tools for processing engineers.
years, there has been less emphasis on developing interdisciplinary skill sets. Geomet aims to integrate geologic and mineralogical information with process planning and metallurgical testwork to create a system of transferable information throughout the life of a project (Fig. 3). From initial airborne and ground geophysics to geologic and alteration mapping and rock and mineral analysis, the information gathered at the front end of a project should be translatable to other (non-geologic) potential users of the information downstream. The communication of project information can significantly reduce costs and increase the value of a project.
GEOMET AS PREDICTIVE METALLURGY The fundamental role of mineral characterization in predicting the metallurgical response of materials traditionally
has been the domain of process mineralogy. When well-trained mineralogists also are familiar with mineral processing methods, process mineralogy can have a very significant role in flowsheet development. A good process mineralogist can demonstrate the importance of mineralogy to process development by showing engineers key ore-gangue relationships, the mineralogical reasons for predicted liberation of an ore mineral, and material characteristics that might impact recovery. This understanding is particularly important for engineers who might otherwise rely on assay analysis and later wonder why recoveries do not match predicted rates. Examples of process mineralogy topics include gold enclosed in pyrite requiring fine grinding and copper-activated pyrite surfaces causing excessive pyrite flotation. Baum (1988) provided a review of process mineralogical factors that can influence epithermal gold and to page 12 . . . gold-silver deposits. In
FIGURE 3. The flow-through of geomet information relies on the initial geologic and mineral characterization conducted at the front end of a project by the geologist, and carried through by many others. The language used should therefore be communicable throughout the project.
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order of impact, these factors include refractoriness, mineralogical ore variation, clay content, acid-forming minerals, permeability, cyanicides, oxygen consumers, sulfate formation, toxic elements, particle size distribution, coarse gold, base metal minerals, and artificial contaminants (Baum, 1988). The Metallurgical Society publication series in process mineralogy (e.g., Hagni, R., 1986; Vassiliou et al., 1987) and Petruk (2000) provide case studies and examples of mineralogical applications to processing and development. In today’s usage, geomet incorporates the principles of process mineralogy and materials characterization as a tool for predictive metallurgy. Metallurgists view geomet as a method for project evaluation that begins with test work on drill core samples. Richardson et al. (2007) defined geomet as “…the geologically informed selection of a number of test samples to determine metallurgical parameters and the distribution of these parameters through an orebody using an accepted geostatistical technique to support process modeling.” The mineral characterization of core, concentrates, and other mining materials influences sampling and testing, and forms part of the input into processing models to determine ore characteristics such as liberation, grindability, aspect ratio, flotability, and leachability (Williams and Richardson, 2004). It is now possible to gain greater understanding of mineralogical and textural variability in geologic samples as a result of the wide variety of analytical tools available. In addition to microprobe, SEM, Rietveld XRD, FTIR, and other standard methods, the new generation of quantitative or automated mineralogical tools such as Intellection’s QEMSCAN® and JKTech’s Mineral Liberation Analyzer ® provide enormous capabilities for mineral composition and image analysis, data management, and process application. The large datasets it is now possible to attain make it possible to statistically determine probable metallurgical outcomes for flowsheet development. In the services sector, the SGS Group (including SGS Lakefield and Minnovex) is ahead of the pack in offering geomet services to mining projects, from prefeasibility study to production and predicting operational success. The SGS method applies mineral characterization to
downstream processing by the use of geometallurgical mapping and modeling techniques and development of a geometallurgical matrix using the physical attributes of a deposit (Williams and Richardson, 2004). The matrix is a useful method of determining the combinations of factors that impact development, and it can be used as a guide for further sampling and testing. A simplified matrix drawn up by a student to illustrate a Carlin trend deposit is illustrated in Figure 4 (Slattery, 2007). The units of the matrix are blocks defined by particular geologic and mineralogical characteristics that can be input into specific comminution and flotation process models. Through the geostatistical analysis of these parameters, the results can be incorporated into mine planning, 3-D block models, and resource valuation calculations (Williams and Richardson, 2004; Dobby et al., 2006).
GEOMET STARTS WITH GEO The renewed interest in geomet results from the drive to reduce operating costs and increase the effectiveness of operations, all the while promoting sustainability and limiting the environmental footprint of an operation. In this regard, the importance of geology to the bottom
FIGURE 4. An example of a simplified matrix analysis of a gold ore using the SGSMinnovex matrix model concept (Dobby et al., 2006), by student Laura Slattery, CSM (Slattery, 2007). Parameters to identify and include in this matrix include rock type, alteration, and specific attributes critical to the deposit. Each block, or combination of parameters, is assigned a predictive processing value that can be directly input into the block model used for the mine.
line now can be better demonstrated and quantified by the geologist for the engineer through new techniques such as quantitative mineralogy. First, it requires an interdisciplinary team representing geology, mineralogy, operations, processing, and metallurgy. Geologists have a fundamental understanding of spatial relationships, mineral and material properties, recrystallization and alteration processes, and the distribution of ores, fractures, and fluids that will impact process development and project valuations. The geologist provides the front-end information describing and delimiting an ore deposit to the project team so that the deposit can be assessed as an economically viable project. The thoroughness with which the geologic materials have been characterized can be one determining factor in the decision to develop a project, but it is only useful if it can be transferred to the rest of the team in a way that is beneficial to project development. Some expenditure in resources must be applied for the geologic data to be reassessed in terms of processing attributes during mapping, drilling, testwork, and mine planning. Extensive mineralogical study may be somewhat costly and time-consuming at the prefeasibility stage, but the advantage to being able to predict metallurgical methods in diverse mine materials will be of greater economic benefit later on. Geomet therefore enters into the financial model of a project as a front-end geologic cost that impacts downstream operational costs (Fig. 5). Detailed materials characterization (rock descriptions, mapping relationships, 3-D ore model, ore-gangue mineral assessment) conducted at the start of a project also reduces project unknowns. Those factors (deleterious elements, mineral variability, or unforeseen clay horizons, for example) that might adversely affect the project can be identified and planned for, and the improved understanding of the materials aids in process optimization. The geologic risk inherent in the project and the chances for unanticipated costs are reduced, while planning and net present value of the project are improved. Kendrick et al. (2003) illustrated the positive cost-recovery impact of geomet characterization in a survey of Phelps Dodge’s Candelaria concentrator. Thorough materials analysis of key ore types in relation to the grinding,
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FIGURE 5. Companies that invest in full-project geomet assessments can improve planning and reduce project risk. As illustrated, the potential for loss can be reduced (black curves, solid to dashed), while anticipated project value can be increased (blue lines, solid to dashed).
flotation, and metallurgical circuits resulted in improved circuit operation, 10% increase in gold recovery, 16% reduced copper tailings, 72% reduced lime use, and improved cash flow by more than $5 million/year (Kendrick et al., 2003). The relationship of geology to processing also is demonstrated in the mill. The energy consumption related to the crushing and grinding circuit can be one of the more costly stages in extraction. A full understanding of rock properties and breakage behavior can be critical to reducing costs and making comminution more efficient. The geologic attributes of rocks provide the linkage between mineralogy, texture, and breakage test results so that the physical properties of materials (rock, core, or concentrate) can be predicted. For a processing engineer to understand what the geologist means by a propylitically altered-calcalkaline-monzodiorite, the material can be redefined in terms of a geomet descriptive terminology such as Texture type T, Fabric type F, Breakage characteristics B, Grinding behavior G, Flotation behavior F, etc, defined by the geologist on the basis of mineral percentages, textural relationships, and rock properties tests. Geologists contribute a wealth of knowledge relating to the distribution of materials, their variability, ore-gangue associations, alteration intensities and variability, and the spatial perspective in three dimensions that the metallurgist may not perceive. Geomet provides
a means for communicating this information and therefore enhances the role of the geologist in a project. In prefeasibility assessment, geologists can use quantitative mineralogy to estimate process methodology, grind size requirements, flotation reagents, and so on, effectively conducting an initial processing assessment long before the project hits the pilot bench. This is not to say that the geologist has the wherewithal to accurately predict metallurgical criteria, nor should he, but he can help to advance a project early on and at lower cost by fully assessing the mineralogical and geologic relationships in terms of anticipated project requirements. In contrast to their university experience, students of resources are unlikely to work in separate departments with large numbers of isolated engineers, geologists, and metallurgists. They should thus become literate in a range of fields that impact their specialty. Hanks (1997) outlined the basic procedures and tests conducted during process development that the exploration geologist should consider when conducting sampling programs. Developments in metallurgy and processing should be regularly reviewed by geologists so they can be considered in early-stage assessments of ore deposits. Such advances include SX-EW, pressure leach and bio leach processes, and potential future developments related to grinding and extraction (Hoal et al., 2006). For geology students this is
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empowering: during the next downturn, geologists with an understanding of processing methods will be able to contribute cost-saving measures to the development stream through improved materials and ore characterization. As mining and metallurgy focus increasingly on process enhancement, the ability of geologists to contribute geologic characterization to the flowsheet will be a career asset. Some of the important components of a project the geologists contribute in development are shown in Figure 6. They can be summarized as (1) project planning: defining the materials and value drivers that may determine the success of a project; (2) materials assessment: identifying the key spatial and compositional relationships in the deposit that will aid in process development; (3) materials testing: helping direct the course of metallurgical decisions by reviewing test results within a geologic framework: and (4) geomet resource model: incorporating attributes into a model that illustrates 3-D variability and can be used for efficient mine planning. Geologic and mineralogical information should be used throughout the development of a project, not only at the front end. Interdisciplinary teams of geologists and mineralogists, as well as operating, processing, and metallurgical engineers, can best provide mine planning evaluation. In project planning, the geologist is instrumental in defining the target, the parameters required for a successful operation such as grade, commodity and tonnage, and value drivers such as throughput, recovery, grade, and cost. Traditional geologic activities occur during the materials assessment stage when field relationships are established, samples and drill core are examined, and mineralogical features are identified. The geomet action item is to identify the key physical attributes and the distribution of those measurable properties that have the potential to significantly impact mineral processing. The geologist can then redefine the spatial distribution of materials in terms of geomet domains; these may not coincide with geologic domains but may more closely follow secondary patterns such as alteration fronts. In materials testing, the methods chosen to measure attributes that have been defined and mapped in geomet domains require geologic input. to page 14 . . . Tests may include
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FIGURE 6. A geomet program depends on excellent initial materials characterization through fieldwork, mapping, and sample study. The geologic components of such a program enter into every phase of the development process (after Williams and Richardson, 2004; Dobby et al., 2006; Hoal et al., 2006; Quantitative Group, 2006; Hoal, 2007; SGS Group, 2008; Wikipedia, 2008).
comminution, leach, or flotation tests that relate to mineral and lithologic features. The geologist should assist in interpretation of test results that reflect the mineralogy of the materials. Materials
variability within the deposit, ore-specific parameters, and properties of material types all have geologic controls. The 3-D aspects of the deposit will become more clearly known as a result of geomet
testwork, and the geologist (who is responsible for making 3-D models of the deposit) can incorporate the distribution of materials with specific processing characteristics into the 3-D model.
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The development of a successful geomet resource model ultimately involves the creation of a matrix that includes geologic, mineralogical, alteration, and test result parameters which are used for mine planning and design (Williams and Richardson, 2004). Geologic reconciliation is an important aspect of the geomet resource model because the geologist can predict to some extent the ore variability and mineralogy changes that may impact rock behavior. This helps in planning forecasting, and in improved valuation of the deposit.
(Hoal, 2007). The geologist’s role in geomet is to ensure that this information is captured, translated into the proper context, and passed down the project chain. The benefits of geomet include enhanced value through project integration. In collaboration with industry, universities are filling the need for training, research, and development of new approaches incorporating geomet. At CSM, the geomet initiative forms part of an overall effort at integrated mineral characterization of a diversity of geologic materials.
SUMMARY
ACKNOWLEDGMENTS
Geomet should incorporate a significant geologic and mineralogical component, both before metallurgists receive samples when a project reaches the process test bench or pilot stage, and also during project development, when materials variability needs to be assessed. A common difficulty in many projects is communicating key information to other members of the team. Geomet offers the opportunity for early input of geologic information into project planning, material testing, and key decisions by redefining and remapping in terms of materials characteristics. The involvement of a geomet team throughout a project’s life has great potential economic benefits. At the front end such analysis aids in characterizing materials for the mine model, and during production recurrent geomet analysis assists with reconciliation and forward planning. Geologists have an important firstuser role to play in defining the materials that may determine the success of a project. They help to identify the key factors that will direct process development, thereby driving geomet decisions. Geologists also are in a position to look beyond the mining industry into other geologic arenas to gain new insights that can benefit mineral extraction. Materials characterization relating mineralogy to rock breakage is also being conducted in the petroleum sector, for example, where the relationship of mineralogy to fluid pathways, rock fracturing properties, and extraction methods has a direct application to mining. The potential pitfalls of geomet are in definitions and in context: confining geomet to predictive metallurgy ignores a wealth of important information that can be redefined in a process context
Many of the ideas in this paper were developed during the 2007 CSM course in Geometallurgy, and in discussions with and projects by students, L. Albuquerque, B. Hardman, M. Koop, M. McGlynn, L. Pesce, J. Ross, C. Seick, L. Slattery, J. Stammer, and C. Wyatt. Industry participants in class discussions and site visits were critical to appreciating the interdisciplinary work currently being conducted in process mineralogy and materials characterization; they include R. Schmidt (Hazen Research), D. Brosnahan and C. Clode (Newmont), W. Baum (Phelps Dodge), and J. Richardson (SGS Minerals). J. Gutzmer and M. Hitzman provided helpful insights and comments in their reviews of this paper.
REFERENCES Baum, W., 1988, Mineralogy-related processing problems, in Carson, D.J.T., and Vassiliou, A.H., eds., Process Mineralogy VIII, The Minerals, Metals, and Materials Society, p. 3−20. Dobby, G., Bennett, C., Bulled, D., and Kosick, G., 2006, Geometallurgical modeling—the new approach to plant design and production forecasting/planning, and mine/mill optimization: Unpublished report, Minnovex Technologies Inc., SGS Minovex. Hagni, R.D., 1986, ed., Process Mineralogy VI: Applications to precious metals deposits, industrial minerals, coal, liberation, mineral processing, agglomeration, metallurgical producst, and refractories, with special emphasis on cathodoluminesence microscopy: Warrendale, The Metallurgical Society, 631 p. Hanks, J.T., 1997, Process development for exploration projects: Society for Mining, Metallurgy, and Exploration, Denver Annual Meeting, Preprint 97-41, 7 p.
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Hoal, K.O., 2007, Benefits and pitfalls of geometallurgy: The importance of mineral characterization: Society of Mining, Metallurgy, and Exploration, Conference on Precious Metals Processing, Tucson, October 5, 2007. Hoal, K.O., McNulty, T.P., and Schmidt, R., 2006, Metallurgical advances and their impact on mineral exploration and mining: Society of Economic Geologists Special Publication 12, p. 243−261. Irving, J.D., 1906, University training of engineers in economic geology: Discussion, Economic Geology, v. 1, p. 77−82. Kendrick, M., Baum, W., Thompson, P., Gilkie, G., and Gottleib, P., 2003, The use of QEMSCAN automated mineral analyzer at the Candelaria concentrator: Chilean Institute of Mining Engineers and the Metallurgical Society of the Canadian Institute of Mining, Metallurgy and Petroleum, COPPER 2003-COBRE 2003: Volume III-Mineral Processing, Santiago, p. 415−430. McQuiston, F.W., Jr. and Bechaud, L.J., Jr., 1968, Metallurgical sampling and testing, in Pfleider, E.P., ed., Surface mining: New York, The American Institute of Mining, Metallurgical, and Petroleum Engineers, p. 103−121. Petruk, W., 2000, Applied mineralogy in the mining industry: Amsterdam, Elsevier, 268 p. Quantitative Group, 2006, Geometallurgical modelling: QG Newsletter, December 2006, p. 3. Richardson, J., Dobbie, G., Martin, C., and Flores, L., 2007, Geometallurgy—linking the geology and the block model to metallurgical processing and production planning [abs.]: Ores & Orogenesis, CircumPacific Tectonics, Geologic Evolution, and Ore Deposits, A symposium, Arizona Geological Society, Tucson, September 24–30, 2007. SGS Group, 2008, Geometallurgy overview: Metallurgical services, http://www.met. sgs.com/geometallurgical_mapping. Slattery, L., 2007, Geometallurgy of the Mega pit, Twin Creeks mine, Humboldt County, Nevada: Course project, MNGN498/598C/ MTGN498B/598A/GEGN498/598C, Golden, Colorado School of Mines, 16 p. Vassiliou, A.H., Hausen, D.M., and Carson, D.J.T., eds.,1987, Process Mineralogy VII: Applications to mineral beneficiation technology and mineral exploration, with special emphasis on disseminated carbonaceous gold ores: Warrendale, The Metallurgical Society, 647 p. Wikipedia, 2008, User:Geomet/Geometal lurgy: http://en.wikipedia.org/wiki/User: Geomet/Geometallurgy. Williams, S.R., and Richardson, J.M., 2004, Geometallurgical mapping: A new approach that reduces technical risk: 36th Annual Meeting of the Canadian Mineral Processors, Canadian Institute of Mining, Metallurgy and Petroleum, Ottawa, Proceedings, Paper 16, 28 p. 1
