economic environmental rock high efficiency concentrator sell at a loss in washington

economic environmental rock high efficiency concentrator sell at a loss in washington

The life cycle of mining begins with exploration, continues through production, and ends with closure and postmining land use. New technologies can benefit the mining industry and consumers in all stages of this life cycle. This report does not include downstream processing, such as smelting of mineral concentrates or refining of metals. The discussion is limited to the technologies that affect steps leading to the sale of the first commercial product after extraction

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The three major components of mining (exploration, mining, and processing) overlap somewhat. After a mineral deposit has been identified through exploration, the industry must make a considerable investment in mine development before production begins. Further exploration near the deposit and further development drilling within the deposit are done while the mining is ongoing. Comminution (i.e., the breaking of rock to facilitate the separation of ore minerals from waste) combines blasting (a unit process of mining) with crushing and grinding (processing steps). In-situ mining, which is treated under a separate heading in this chapter, is a special case that combines aspects of mining and processing but does not require the excavation, comminution, and waste disposal steps. The major components can also be combined innovatively, such as when in-situ leaching of copper is undertaken after conventional mining has rubblized ore in underground block-caving operations

Modern mineral exploration has been driven largely by technology. Many mineral discoveries since the 1950s can be attributed to geophysical and geochemical technologies developed by both industry and government. Even though industrial investment in in-house exploration research and development in the United States decreased during the 1990s, new technologies, such as tomographic imaging (developed by the medical community) and GPS (developed by the defense community), were newly applied to mineral exploration. Research in basic geological sciences, geophysical and geochemical methods, and drilling technologies could improve the effectiveness and productivity of mineral exploration. These fields sometimes overlap, and developments in one area are likely to cross-fertilize research and development in other areas

3 technologies in exploration, mining, and processing

Underlying physical and chemical processes of formation are common to many metallic and nonmetallic ore deposits. A good deal of data is lacking about the processes of ore formation, ranging from how metals are released from source rocks through transport to deposition and post-deposition alteration. Modeling of these processes has been limited by significant gaps in thermodynamic and kinetic data on ore and gangue (waste) minerals, wall-rock minerals, and alteration products. With the exception of proprietary data held by companies, detailed geologic maps and geochronological and petrogenetic data for interpreting geologic structures in and around mining districts and in frontier areas that might have significant mineral deposits are not available. These data are critical to an understanding of the geological history of ore formation. A geologic database would be beneficial not only to the mining industry but also to land-use planners and environmental scientists. In many instances, particularly in arid environments where rocks are exposed, detailed geologic and alteration mapping has been the key factor in the discovery of major copper and gold deposits

Most metallic ore deposits are formed through the interaction of an aqueous fluid and host rocks. At some point along the fluid flow pathway through the Earth’s crust, the fluids encounter changes in physical or chemical conditions that cause the dissolved metals to precipitate. In research on ore deposits, the focus has traditionally been on the location of metal depositions, that is, the ore deposit itself. However,

the fluids responsible for the deposit must continue through the crust or into another medium, such as seawater, to maintain a high fluid flux. After formation of a metallic ore deposit, oxidation by meteoric water commonly remobilizes and disperses metals and associated elements, thereby creating geochemical and mineralogical haloes that are used in exploration. In addition, the process of mining commonly exposes ore to more rapid oxidation by meteoric water, which naturally affects the environment. Therefore, understanding the movement of fluids through the Earth, for example, through enhanced hydrologic models, will be critical for future mineral exploration, as well as for effectively closing mines that have completed their life cycle (NRC, 1996b)

The focus of research on geological ore deposits has changed with new mineral discoveries and with swings in commodity prices. Geoscientists have developed numerous models of ore deposits (Cox and Singer, 1992). Models for ore deposits that, when mined, have minimal impacts on the environment (such as deposits with no acid-generating capacity) and for deposits that may be amenable to innovative in-situ extraction will be important for the future. Because the costs of reclamation, closure, postmining land use, and long-term environmental monitoring must be integrated into mine feasibility studies, the health and environmental aspects of an orebody must be well understood during the exploration stage (see Sidebars 3-1 and 3-2). The need for characterizations of potential waste rock and surrounding wall rocks, which may either serve as chemical buffers or provide fluid pathways for escape to the broader environment. Baseline studies to determine hydrologic conditions and natural occurrences of potentially toxic elements in rocks, soils, and waters are also becoming critical. The baseline data will be vital to determining how mining may change hydrologic and geochemical conditions. Baseline climatological, hydrological, and mineralogical data are vital; for example, acid-rock drainage will be greatly minimized in arid climates where natural oxidation has already destroyed acid-generating sulfide minerals or where water flows are negligible

3 technologies in exploration, mining, and processing

A wealth of geologic data has been collected for some mining districts, but the data are not currently being used because much of the data is on paper and would be costly to convert to digital format. Individual companies have large databases, but these are not available to the research community or industrial competitors. Ideally, geological research on ore deposits should be carried out by teams of geoscientists from industry, government, and academia. Industry geoscientists have access to confidential company databases and a focus on solving industrial problems; government and academic geoscientists have access to state-of-the-art analytical tools and a focus on tackling research issues. Currently, geological research activities in the United States are not well coordinated and are limited primarily to studies of individual deposits by university groups and, to a much lesser extent, by the USGS. More effective research is being carried out in Australia and Canada by industry consortia working with government and academia to identify research problems, develop teams with the skills appropriate to addressing those problems, and pool available funding. Both Canada and Australia have resolved issues of intellectual property rights in the industry-university programs, but these issues have yet to be resolved in the United States

Surface geochemical prospecting involves analyzing soil, rock, water, vegetation, and vapor (e.g., mercury and hydrocarbons in soil gas) for trace amounts of metals or other elements that may indicate the presence of a buried ore deposit. Geochemical techniques have played a key role in the discovery of numerous mineral deposits, and they continue to be a standard method of exploration. With

Ore has traditionally been defined as natural material that contains a mineral substance of interest and that can be mined at a profit. The costs of mine closure and reclamation of the site now constitute a significant portion of mining cost. Hence, ore bodies that can be mined in a way that produces virtually no waste and that leaves a small surface “footprint” may have distinct economic and environmental advantages over ore bodies that produce large amounts of waste and create large land disturbances. Until recently, these criteria have generally not figured significantly in decisions about mineral exploration. Exploration geologists are now developing new ore-deposit models to improve the chances of finding such “environmentally friendly” ore bodies

3 technologies in exploration, mining, and processing

The copper ore bodies mined from 1911 to 1938 at Kennecott, Alaska (now within the Wrangell–St. Elias National Park and Preserve), are examples of potentially environmentally “friendly” ore deposits. The ore bodies consisted of veins of massive chalcocite (a mineral consisting of copper and sulfur). The deposits contained nearly 4.5 million tons of 13 percent copper and 65 grams of silver per ton, some of the highest grade deposits ever mined (Bateman, 1942). The ore at Kennecott contained an amount of copper equivalent to a 100-million-ton typical porphyry copper deposit, which is currently one of the primary types of copper deposits being mined worldwide

The Kennecott deposits were an economically attractive target for exploration. They were also environmentally attractive because they had a large amount of copper in a small volume of rock, so extraction would cause minimal disturbance, and they consisted primarily of chalcocite with little or no iron sulfide that would produce acid-rock drainage. In addition, their location within massive carbonate rock ensured that any acid generated by the oxidation of sulfides would be quickly neutralized (Eppinger et al., 2000)

Deposits similar to those at Kennecott have not been a target for exploration by many companies primarily because exploration geologists have not developed a robust exploration model for this type of deposit and because their small size makes them difficult to locate. Nevertheless, the development of new, robust models for locating deposits of this and other types of ore bodies that can be mined with little adverse environmental impact could have important economic benefits

3 technologies in exploration, mining, and processing

increasingly sophisticated analytical techniques and equipment developed in the past 50 years, exploration geologists have been able to detect smaller and smaller concentrations of the elements of interest. Available analytical tools are sufficient for most types of analyses required by the industry. However, new technologies, such as laser fluorescence scanning and portable X-ray fluorescence, which can directly determine concentrations of elements in rocks, and differential leaching techniques are also being developed and used for exploration. As analytical equipment is miniaturized, inexpensive hand-held devices that could be used in the field or in mines to provide real-time analytical results would significantly benefit both mineral exploration and mining, as well as environmental regulators

Other research that could benefit the minerals industry includes the development of a more thorough understanding of the media being sampled, such as soils. The complex processes that result in soil formation and the behavior of various elements in different soil types are still poorly understood. A recent NRC report on Basic Research Opportunities in Earth Sciences calls for multidisciplinary integrative studies of soils (NRC, 2001). Fundamental research in soil science could produce significant spin-offs that would affect geochemical exploration and would contribute to a more thorough understanding of soil ecology for agriculture. Geoscientists are just beginning to understand how organisms concentrate metals. Even though geobotanical exploration was used by a number of companies in the 1970s and 1980s, research in this field, together with investigations of metal concentrations by other organisms, such as bacteria and fungi, has not been focused on mineral exploration. Other relevant areas of research include soil-gas geochemistry and water geochemistry. The NRC report on Basic Research Opportunities in Earth Sciences also highlighted the need for geobiological research (NRC, 2001)

Industrial research and development in geophysical methods of mineral exploration have been ongoing since World War II. Canada has led the world in geophysical innovations, primarily through industry support for academic programs and through in-house corporate development of new techniques. An example of the latter is the recent development by the mining industry of a prototype airborne gravity system. Gravity measurements are a typical means of locating dense metallic mineral deposits and of mapping different rock types in the Earth’s crust. However, traditional ground-based surveys are time consuming and therefore expensive. As an NRC report in 1997 pointed out, the ability to gather gravity data from an aircraft would significantly increase productivity and reduce the invasiveness of mineral exploration (NRC, 1997b)

3 technologies in exploration, mining, and processing

Magnetic surveys are commonly conducted by aircraft that must fly at a fixed distance above the ground surface for optimal data acquisition (Figures 3-1 and 3-2). These surveys are difficult to conduct and risky in rugged terrain. The

recent development of drones, primarily by the U.S. military, has made more effective geophysical surveys possible. This technology is currently being explored by industry-government consortia in Australia

Seismic exploration, although already an integral part of petroleum exploration, is rarely used in mineral exploration. The primary reasons are technological and economic. Current seismic technology is used to gather data at relatively great depths (thousands of meters below those typical of mineral deposits). Near-surface seismic imaging is possible but will require the development of new strategies for collecting and processing the data (NRC, 2000). Typical seismic surveys are expensive in terms of data collection and data processing. New computing capabilities have led to cost reductions although the costs are still beyond most budgets for mineral exploration. Thus, seismic companies have had little financial incentive to engage in this type of research and development, and virtually no governmental support has been available

3 technologies in exploration, mining, and processing

Remote sensing is the recording of spectral data (visible to infrared and ultraviolet wavelengths) from the Earth’s surface via an airborne platform, generally a high-flying aircraft, or from near-Earth orbit (NRC, 2000). Government support was critical in initiating this technology. Current technologies include the Landsat thematic mapper and the enhanced thematic mapper multispectral imager by the United States and high-resolution panchromatic imaging technology (SPOT) developed by the French Space Agency, as well as radar imaging (RadarSat) of topography for cloud-covered or heavily vegetated areas. The U.S. government transferred some existing systems to the commercial sector, and several privately owned satellites are currently in operation and providing detailed (4-meter resolution) multispectral imagery. These data are used by the mineral exploration sector, as well as many other industrial, academic, and government groups. Promising new multispectral technologies are being developed by both government and industry groups. The shuttle radar topographic mapping (SRTM) system will provide high-quality, detailed digital topographic and image data. The advanced spaceborne and thermal emission and reflection (ASTER) mission will provide multiband thermal data

Hyperspectral technologies are being developed to gather additional data that can be used to map the mineralogy of the ground surface. A high-altitude aircraft system, airborne visible/infrared imaging spectrometer (AVIRIS), has been developed by the National Aeronautics and Space Administration (NASA). Data from this sensor have been successfully used for both mineral exploration and mine closures at several sites in the United States. Spaceborne hyperspectral systems are also being developed. The Hyperion is being

readied for deployment on the Earth Observing-1 (EO-1) satellite. Foreign systems include the Orbview-4 (Warfighter) and the airborne infrared echelle spectrometer (AIRES) instrument being developed by Australia

3 technologies in exploration, mining, and processing

Currently, a number of research challenges are being addressed for hyperspectral technology, especially for spaceborne systems. These include the development of focal planes with adequate signal-to-noise spectral resolution to resolve mineral species of importance and the capability of acquiring data at a 10-meter spatial resolution while maintaining a minimum swath width of 10 kilometers. The focal planes must also be compact, lightweight, have accurate pointing capabilities, and be robust enough to maintain calibration for long-duration spaceflights

Routine use of existing hyperspectral systems by the minerals industry has been hampered by the unavailability of systems for industrial use, the high cost of hyperspectral data (when available) compared to typical multispectral data, and the need for additional research into the processing of hyperspectral data. Government support for system development and deployment, as well as for basic research on the analysis of hyperspectral data, would ensure that these new technologies would be useful for the mineral exploration industry, as well as for a wide range of other users, including land-use planners and environmental scientists

Almost all mineral exploration involves drilling to discover what is below the surface. No significant changes in mineral drilling technology or techniques have been made for more than three decades (NRC, 1994b). This contrasts sharply with spectacular advances in drilling technologies, including highly directional drilling, horizontal drilling, and a wide range of drilling tools for the in-situ measurement of rock properties, for the petroleum and geothermal sectors. Mineral exploration involves both percussion and rotary drilling that produce rock chips and intact samples of core. The diameter of mineral exploration drill holes (called slimholes) is generally much smaller than the diameter of either petroleum or geothermal wells. Therefore, many of the down-hole tools used for drilling in the petroleum and geothermal fields are too large to be used in the mineral exploration slimholes. The need for miniaturization of existing drilling equipment is growing not only in the mineral industry but also for NASA to investigate drilling on Mars. The development of guided microdrill systems for the shallow depths of many mineral exploration projects will be challenging

3 technologies in exploration, mining, and processing

Drilling generally represents the largest single cost associated with mineral exploration and the delineation of an ore deposit once it has been discovered. Hundreds of drill holes may be required to define the boundaries and evaluate the quality of an orebody. Decreasing the number of drill holes, increasing the drilling rate, or reducing the energy requirements for drilling would have a substantial impact on mineral exploration and development costs. In many situations directional drilling could significantly reduce the number of drill holes required to discover a resource in the ground. Novel drilling technologies, such as down-hole hammers, turbodrills, in-hole drilling motors, and jet drilling systems, have the potential to increase the drilling rate. Novel technologies, together with more efficient rock bits, could also reduce energy requirements for drilling

Down-hole logging is a standard technique in petroleum exploration. However, it is rarely used in mineral exploration. Standard petroleum well-logging techniques include gamma-ray surveys (to distinguish different rock types based on natural radioactivity), spontaneous potential (to determine the location of shales and zones with saline groundwater), mechanical caliper and dipmeter test (to determine dip and structure of the rock mass penetrated), and a variety of other geophysical tests (resistivity, induction, density, and neutron activation). These tests determine the physical properties of the drilled rock mass and differentiate rock types. Typically, the minerals industry has obtained some of this information by taking samples of rock (either drill chips or drill cores) for analysis. The development of down-hole analytical devices, such as spectrometers, would make it possible to conduct in-situ, real-time analyses of trace elements in the rock mass that could dramatically shorten the time required to determine if a drill hole had “hit” or not. Miniaturization will be necessary for existing down-hole technologies to be used in slimholes

Drilling and access for drilling generally represent the most invasive aspect of mineral exploration. The environmental impacts of exploration activities could be significantly reduced by the development of drilling technologies that would minimize the footprint of these activities on the ground, such as the miniturization of drilling rigs, the ability to test larger areas from each drill site, and better initial targeting to minimize the number of holes

3 technologies in exploration, mining, and processing

Numerous opportunities exist for research and development that would significantly benefit exploration (Table 3-1), many of which involve the application of existing technologies from other fields. Support for technological development, primarily the miniaturization of drilling technologies and analytical tools, could dramatically improve the efficiency of exploration and improve the mining process. Although industry currently supports the development of most new geochemical and geophysical technologies, basic research on the chemistry, biology, and spectral characterization of soils could significantly benefit the mineral industry. Continued government support for spaceborne remote sensing, particularly hyperspectral systems, will be necessary to ensure that this technology reaches a stage at which it could

be commercialized. In the field of geological sciences more support for basic science, including geological mapping and geochemical research, would provide significant though gradual improvements in mineral exploration. Filling gaps in fundamental knowledge, including thermodynamic-kinetic data and detailed four-dimensional geological frameworks of ore systems, would provide benefits not only for mineral exploration and development but also for mining and mineral processing. The thermodynamic-kinetic data would lead to a better understanding of how the ore systems evolved through time, how the minerals in the ores and waste rocks will react after exposure to postmining changes in hydrology, and how new processing technologies should be developed. The geological framework of an ore system includes the three-dimensional distribution of rock types and structure, such as faults and fractures, as well as the fourth dimension of time—how the rocks and structures formed. This framework is important to successful exploration, efficient mining, and later reclamation. Focused research on the development of exploration models for “environmentally friendly” ore deposits might yield important results in the short term. A mechanism for focusing research on the most important issues, as identified by industry, would help focus industrial, governmental, and academic resources on these problems

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