Mining techniques can be divided into two common excavation types: surface mining and sub-surface (underground) mining. Today, surface mining is much more common, and produces, for example, 85% of minerals (excluding petroleum and natural gas) in the United States, including 98% of metallic ores.]
Targets are divided into two general categories of materials: placer deposits, consisting of valuable minerals contained within river gravels, beach sands, and other unconsolidated materials; and lode deposits, where valuable minerals are found in veins, in layers, or in mineral grains generally distributed throughout a mass of actual rock. Both types of ore deposit, placer or lode, are mined by both surface and underground methods.
Some mining, including much of the rare earth elements and uranium mining, is done by less-common methods, such as in-situ leaching: this technique involves digging neither at the surface nor underground. The extraction of target minerals by this technique requires that they be soluble, e.g., potash, potassium chloride, sodium chloride, sodium sulfate, which dissolve in water. Some minerals, such as copper minerals and uranium oxide, require acid or carbonate solutions to dissolve
Surface mining is done by removing (stripping) surface vegetation, dirt, and, if necessary, layers of bedrock in order to reach buried ore deposits. Techniques of surface mining include: open-pit mining, which is the recovery of materials from an open pit in the ground, quarrying, identical to open-pit mining except that it refers to sand, stone and clay; strip mining, which consists of stripping surface layers off to reveal ore/seams underneath; and mountaintop removal, commonly associated with coal mining, which involves taking the top of a mountain off to reach ore deposits at depth. Most (but not all) placer deposits, because of their shallowly buried nature, are mined by surface methods. Finally, landfill mining involves sites where landfills are excavated and processed. Landfill mining has been thought of as a solution to dealing with long-term methane emissions and local pollution.
High wall mining is another form of surface mining that evolved from auger mining. In high wall mining, the coal seam is penetrated by a continuous miner propelled by a hydraulic Push-beam Transfer Mechanism (PTM). A typical cycle includes sumping (launch-pushing forward) and shearing (raising and lowering the cutter-head boom to cut the entire height of the coal seam). As the coal recovery cycle continues, the cutter-head is progressively launched into the coal seam for 19.72 feet (6.01 m). Then, the Push-beam Transfer Mechanism (PTM) automatically inserts a 19.72-foot (6.01 m) long rectangular Push-beam (Screw-Conveyor Segment) into the center section of the machine between the Powerhead and the cutter-head. The Push-beam system can penetrate nearly 1,000 feet (300 m) into the coal seam. One patented high wall mining system uses augers enclosed inside the Push-beam that prevent the mined coal from being contaminated by rock debris during the conveyance process. Using a video imaging and/or a gamma ray sensor and/or other Geo-Radar systems like a coal-rock interface detection sensor (CID), the operator can see ahead projection of the seam-rock interface and guide the continuous miner’s progress. High wall mining can produce thousands of tons of coal in contour-strip operations with narrow benches, previously mined areas, trench mine applications and steep-dip seams with controlled water-inflow pump system and/or a gas (inert) venting system.
Mantrip used for transporting miners within an underground mine
Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits. Ore, for processing, and waste rock, for disposal, are brought to the surface through the tunnels and shafts. Sub-surface mining can be classified by the type of access shafts used, the extraction method or the technique used to reach the mineral deposit. Drift mining utilizes horizontal access tunnels, slope mining uses diagonally sloping access shafts, and shaft mining utilizes vertical access shafts. Mining in hard and soft rock formations require different techniques.
Other methods include shrinkage stope mining, which is mining upward, creating a sloping underground room, long wall mining, which is grinding a long ore surface underground, and room and pillar mining, which is removing ore from rooms while leaving pillars in place to support the roof of the room. Room and pillar mining often leads to retreat mining, in which supporting pillars are removed as miners retreat, allowing the room to cave in, thereby loosening more ore. Additional sub-surface mining methods include hard rock mining, which is mining of hard rock (igneous, metamorphic or sedimentary) materials, bore hole mining, drift and fill mining, long hole slope mining, sub level caving, and block caving.
Iron hydroxide precipitate stains a stream receiving acid drainage from surface coal mining.
Environmental issues can include erosion, formation of sinkholes, loss of biodiversity, and contamination of soil, groundwater and surface water by chemicals from mining processes. In some cases, additional forest logging is done in the vicinity of mines to create space for the storage of the created debris and soil. Contamination resulting from leakage of chemicals can also affect the health of the local population if not properly controlled. Extreme examples of pollution from mining activities include coal fires, which can last for years or even decades, producing massive amounts of environmental damage.
Mining companies in most countries are required to follow stringent environmental and rehabilitation codes in order to minimize environmental impact and avoid impacting human health. These codes and regulations all require the common steps of environmental impact assessment, development of environmental management plans, mine closure planning (which must be done before the start of mining operations), and environmental monitoring during operation and after closure. However, in some areas, particularly in the developing world, government regulations may not be well enforced.
For major mining companies and any company seeking international financing, there are a number of other mechanisms to enforce environmental standards. These generally relate to financing standards such as the Equator Principles, IFC environmental standards, and criteria for Socially responsible investing. Mining companies have used this oversight from the financial sector to argue for some level of industry self-regulation. In 1992, a Draft Code of Conduct for Transnational Corporations was proposed at the Rio Earth Summit by the UN Centre for Transnational Corporations (UNCTC), but the Business Council for Sustainable Development (BCSD) together with the International Chamber of Commerce (ICC) argued successfully for self-regulation instead.
This was followed by the Global Mining Initiative which was begun by nine of the largest metals and mining companies and which led to the formation of the International Council on Mining and Metals, whose purpose was to “act as a catalyst” in an effort to improve social and environmental performance in the mining and metals industry internationally. The mining industry has provided funding to various conservation groups, some of which have been working with conservation agendas that are at odds with an emerging acceptance of the rights of indigenous people – particularly the right to make land-use decisions.
Certification of mines with good practices occurs through the International Organization for Standardization (ISO). For example, ISO 9000 and ISO 14001, which certify an “auditable environmental management system”, involve short inspections, although they have been accused of lacking rigor. Certification is also available through Ceres’ Global Reporting Initiative, but these reports are voluntary and unverified. Miscellaneous other certification programs exist for various projects, typically through nonprofit groups.
The purpose of a 2012 EPS PEAKS paper was to provide evidence on policies managing ecological costs and maximise socio-economic benefits of mining using host country regulatory initiatives. It found existing literature suggesting donors encourage developing countries to:
- Make the environment-poverty link and introduce cutting-edge wealth measures and natural capital
- Reform old taxes in line with more recent financial innovation, engage directly with the companies, enacting land use and impact assessments, and incorporate specialized support and standards agencies.
- Set in play transparency and community participation initiatives using the wealth accrued.
Mining Policy Framework
Agropet has a global intergovernmental policy on mining and sustainable development.
Mining is an activity that is complex and requires significant capacity for its proper management. The opportunity mining provides to generate benefits must be used effectively to advance sustainable economic development and reduce poverty.
This is why the Agropet is trying to established the Mining Policy Framework (MPF) for member countries. It represents the best practices required for good environmental, social and economic governance of the mining sector and the generation and equitable sharing of benefits in a manner that will contribute to sustainable development.
Agropet overarching objective is enhancing capacities to achieve sustainable development objectives through good governance in the mining sector. This effort is largely framed by its flagship Mining Policy Framework (MPF), which sets out concrete objectives and processes for good governance. Members are committed to reviewing and updating this tool on a regular basis.
Assessments and Reports
Agropet Nigeria Limited is committed to implementing their sustainable mining goals.
Numerous members have requested assistance from Agropet in evaluating their policies through Mining Policy Framework (MPF) Assessments.
Agropet working with a voluntary selection of its member states to help them operationalize practices consistent with the its Mining Policy Framework (MPF). The first assessments were carried out in 2014 in the Dominican Republic, Madagascar and Uganda. Based on the success of these initial evaluations, the IGF now conducts three or four assessments each year, in response to member requests.
The results of these assessments are published in order to help governments target their efforts in implementing the MPF, to inform capacity-building efforts and to allow for monitoring of progress over time.
Find out more about how the process works online. Please see below for reports on assessments conducted to date.