The Five Stages of the Mining Cycle
There are the five stages in the life of a mine starting with exploration and going on to permitting, construction, mining and processing, and eventually closure. Together, they comprise the five stages of the mining cycle.
Exploration, the search for valuable mineral deposits, begins with careful surface observation by prospectors and geologists. In some cases, traditional knowledge can help prospectors and geologists identify favorable areas to explore.
Surface observations commonly lead to extensive sampling and chemical analyses of rocks, soils, and sediments to determine if valuable minerals are present. If they are, drilling is needed to characterize the subsurface extent of the valuable minerals. Drilling recovers core of the underground rock. Cores are essentially tubes of solid rock recovered by the drill â€“ down to depths of a 3000 feet or so but commonly within a few to several hundred feet of the surface.
The core shows the geologist where and how the valuable minerals occur in the rock. It can take several years and hundreds of drill holes to decide if a mineral deposit contains parts that can be profitably mined. These parts are called "ore".
Finding an ore deposit is not enough to start a new mine - government approval is needed before mining can begin. These approvals are provided in permits issued by government regulatory agencies for specific actions in developing and operating mine.
Permits provide agency guidelines, oversight, and monitoring to protect air, soil, and water quality during all stages of mine development and operation. It commonly takes several years and as many as 50 permits from government agencies before mining can start.
The National Environmental Policy Act or NEPA provides a key foundation of the permitting process. NEPA establishes ways for all citizens to engage with regulatory agencies in identifying social, environmental, and economic concerns that should be addressed in permitting new mine developments.
If the mining company gets all of the necessary permits, the next step is construction. Constructing new mines in Alaska commonly requires much new infrastructure including roads, ports, airfields, worker facilities, and ways to generate and transport power. Construction can take two to three years and once construction is complete, mining operations can begin.
Mining and Processing
Mining can be underground or in large surface excavations called open pits. In all cases, ore and surrounding rock that must be removed (waste rock) is broken up by blasting. Ore is hauled or moved on conveyors to processing facilities and waste rock is disposed of nearby.
Processing first involves further breaking of the ore by crushing and grinding. Flotation is a common way valuable minerals are separated and concentrated from ground-up ore. Other steps in processing may include melting, electrolysis, and chemical leaching.
Valuable minerals are extracted from the ore using a variety of methods such as grinding and flotation, heating, electrolysis and chemical leaching. The photo at right shows grinders which are reducing the mineral bearing rock into powder.
The last stage in a mines life is closure. Eventually all the ore is mined and processed and the mine closes. When this happens facilities are removed and the disturbed land is stabilized, covered with soil, and re-vegetated. This is called reclamation. How reclamation is done, particularly to waste rock and tailings disposal areas, is important to protecting the soil and water quality.
An important aspect of closure is that it is planned for before the mine ever starts. A bond is required by law to provide the money to cover the eventual costs of land reclamation. This is insurance that reclamation will be accomplished even if the mine is not as successful as initially thought or the company goes bankrupt.
Images Courtesy United States Geological Survey; Image source: Earth Science World Image Bank