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). 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. Geoscientists have developed numerous models of ore deposits (Cox and Singer, 1992). The focus of research on geological ore deposits has changed with new mineral discoveries and with swings in commodity prices. 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). In addition, the process of mining commonly exposes ore to more rapid oxidation by meteoric water, which naturally affects the environment. 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. The fluids responsible for the deposit must continue through the crust or into another medium, such as seawater, to maintain a high fluid flux. In research on ore deposits, the focus has traditionally been on the location of metal depositions, that is, the ore deposit itself. 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. Most metallic ore deposits are formed through the interaction of an aqueous fluid and host rocks. 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.
A geologic database would be beneficial not only to the mining industry but also to land-use planners and environmental scientists. These data are critical to an understanding of the geological history of ore formation. 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. 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. 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. Underlying physical and chemical processes of formation are common to many metallic and nonmetallic ore deposits. 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. 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. 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). Further exploration near the deposit and further development drilling within the deposit are done while the mining is ongoing. After a mineral deposit has been identified through exploration, the industry must make a considerable investment in mine development before production begins. The three major components of mining (exploration, mining, and processing) overlap somewhat. The discussion is limited to the technologies that affect steps leading to the sale of the first commercial product after extraction. This report does not include downstream processing, such as smelting of mineral concentrates or refining of metals. New technologies can benefit the mining industry and consumers in all stages of this life cycle. The life cycle of mining begins with exploration, continues through production, and ends with closure and postmining land use.