Office of Wastewater Management - Hardrock Mining Overview (2024)
Definition
Hardrock mining involves uncovering and extracting non-fuel metal and mineral deposits of solid ores or eroded deposits in streambeds. Eleven common minerals mined are copper, gold, iron ore, lead, molybdenum, phosphate rock, platinum, potash, silver, uranium, and zinc.
Mining Activities
Hardrock mining involves three basic steps: exploration, extraction, and beneficiation.
Exploration Exploration involves locating and evaluating a suitable ore. Several mineral exploration methods are:
Surveys help identify conditions indicating the potential for an economically recoverable mineral deposit. A desk top survey includes a review of aerial photographs, geologic and geophysical maps, and published reports. A site survey often includes stream, sediment, and rock sampling. One valuable form of site surveys is remote sensing. Most naturally occurring materials absorb sunlight at specific wavelengths. Each mineral has a unique spectral signature related to its chemical composition, grain size, degree of cystallinity, and temperature of formation. The spectral signature is a measure of how reflected sunlight interacts with a surface. Aircraft or satellite systems can remotely collect spectral information over vast areas and thus determine the potential locations of ore deposits.
Drilling is typically undertaken if geologic conditions are promising and surface sampling indicates a possible ore body. Drilling is used to obtain core samples of the ore body at various depths for inspection and analysis. If further exploration of the potential deposit is necessary, drilling can be used to delineate the boundaries of the deposit, as well as the size and grades of the ore. Sophisticated statistical methods are used to infer the characteristics of ore bodies based on a limited number of samples.
Seismic Surveys rely on shock waves produced by small explosives detonated at or near the surface. Electronic receivers known as geophones are placed in strategic locations to measure the speed of shock waves, which travel at different speeds through different geological formations. A seismic survey measures the time it takes shock waves to reflect from various points between formations of different densities. This information may indicate the existence of certain geologic formations of interest.
Although not directly related to exploration, other activities are critical in establishing a mining operation, including the following:
Site development includes construction of access and haul roads, rail lines,
barge terminals, and utilities.
Construction of mining facilities involves construction of shafts, support
buildings, and housing facilities.
Construction of beneficiation facilities includes construction of pipelines,
conveyance systems, leach pads (if needed), processing ponds, and a mill (if
necesscary).
Extraction Extraction involves removing ore deposit from the ground. The two basic types of extraction are surface mining and underground mining.
Surface Mining, the most common form of hardrock mining in use today, consists of extracting the ore by digging. The costs of machines and maintenance for surface mining are low compared to those for underground mining. The basic steps of surface mining are:
1. Overburden, or waste rock, removal: The amount of waste rock that must be
removed varies, but is often enormous. The less valuable materials normally
associated with the more valuable ore deposits are termed gangue materials.
2. Blasting: Explosive charges are detonated to break up the waste rock and ore.
3. Mucking: Heavy machinery removes and transports the ore.
4. Primary crushing: The ore passes through primary crushing to reduce the size of
the material to transport to the mill.
5. Hauling: Trucks, rail cars, or conveyors move the ore from the mine to the mill.
The two main forms of surface mining are open pit and strip mining:
Open pit mining is the most common method of extraction and involves a
concentated excavation. The size of an open pit mine can vary from a small
and superficial site to a pit more than 1000 feet deep and several square
miles in area. Although the same techniques are used to develop mines, each
mine is unique and its final structure depends on topography, the location
and size of the ore, the mineralization of the ore, and other factors.
Strip mining is used to extract horizontal, near surface ore deposits (e.g.,
phosphate). Strip mining progresses linearly and yields long disturbances.
Figure 2 illustrates strip mining.
Underground mining involves digging vertical shafts and horizontal tunnels, or adits, to recover ore deposits. Underground mining is more expensive and requires more skilled workers and specialized equipment than surface mining. Underground mines must enable workers to access, break, and remove the ore. Figure 3 illustrates an underground mining scene.
Beneficiation Beneficiation is the processing of ore to separate the target mineral from the waste rock. Before beneficiation, nearly all crude ore must be reduced in size. Primary crushing reduces ore from 2-4 feet boulders to rocks 8-10 inches in diameter. Secondary crushing reduces the ore into pieces less than 1 inch in diameter. Large rotating cylinders grind the material, creating finely ground mill. Slurry is formed when water is added to finely ground mill.
The type and extent of beneficiation depend on the desired product. Some common types of beneficiation are:
Gravity separation relies on large differences in density between the target
metal (e.g., gold) and the materials in which it is found. It also requires that
the target metal cannot be bound to the surrounding rock matrix. Some
devices used in gravity separation are trommels, sluices, spiral
concentrators, cyclones, jigs, and shaker tables.
Floation is adaptable to small particals and commonly used to recover lead,
copper, platinum, and zinc. In floatation, the addition of a reagent chemical
to ore slurry causes the minerals to become less dense than the gangue and
rise to the top of the tank.
Leaching is the process of extracting a soluble metallic compound from ore. It
involves dissolving the ore with a suitable solvent, such as sufuric acid or
Hardrock mining involves uncovering and extracting non-fuel metal and mineral deposits
mineral deposits
A field is a mineral deposit containing a metal or other valuable resources in a cost-competitive concentration. It is usually used in the context of a mineral deposit from which it is convenient to extract its metallic component.
https://en.wikipedia.org › wiki › Field_(mineral_deposit)
of solid ores or eroded deposits in streambeds. Eleven common minerals mined are copper, gold, iron ore, lead, molybdenum, phosphate rock, platinum, potash, silver, uranium, and zinc.
When a suitable location is found for recovering gold-rich ore, a horizontal shaft is excavated, then a vertical shaft is drilled. The ore is then cut out of the mountain by using large drills and black powder or dynamite, then hoisting those chunks of rock to the surface with ore carts and other bucket rigs.
In a few cases, dust can contain arsenic, lead, and other toxic heavy metals. Particulate matter is an environmental concern because it can contaminate air. It can also deposit dust in surface water, causing sedimentation and turbidity. By its very nature, mining can cause large disturbances to the land.
Waste rocks are rocks that are mined to access the ore. Having a waste rock management plan is important to limit mining effects on nature and the environment. Waste rocks are rocks that are not 'ore' (the mineable part of the rock that is financially viable) in a mine.
The Hardrock Mining and Reclamation Act (H.R. 2262), instituted royalty payments for minerals taken from public lands, established modern environmental standards and bonding requirements for mine operations and accelerated cleanup of abandoned mines.
Hardrock mining on public lands — which includes gold, silver, copper, uranium, lithium, and nearly all critical minerals — is still governed by the General Mining Law of 1872, a law born out of the California Gold Rush that allows mining companies to stake claims on the vast majority of public lands regardless of ...
The mining industry operates through a sequence of stages: exploration, discovery, development, production and reclamation. All stages of this Mining Cycle provide direct economic stimulus.
Acid generation and drainage affect both surface water and groundwater. The sources of surface water contamination are leachate from mine openings, seepage and discharges from waste rock, tailings, ground water seepage, and surface water runoff from waste rock and tailings piles.
Mining can cause erosion, sinkholes, loss of biodiversity, or the contamination of soil, groundwater, and surface water by chemicals emitted from mining processes. These processes also affect the atmosphere through carbon emissions which contributes to climate change.
The major potential environmental impacts associated with mining and associated mineral processing operations are related to erosion-prone landscapes, soil and water quality, and air quality.
There are four main types of waste management, and understanding them can help businesses develop effective waste management strategies. There are four types of waste management: landfill, incineration, recycling, and composting.
Waste rock can be a source of toxic, reactive materials, such as acid rock drainage and heavy metals such as arsenic. All of these can adversely impact aquatic and other organisms, as well as surface and ground waters.
Mineral processing wastes are referred to in the Resource Conservation and Recovery Act (RCRA) as wastes that are generated during the extraction and beneficiation of ores and minerals. These wastes can be subdivided into a number of categories: waste rock, mill tailings, coal refuse, wash slimes, and spent oil shale.
Hardrock mining involves three basic steps: exploration, extraction, and beneficiation. Exploration involves locating and evaluating a suitable ore. Several mineral exploration methods are: Surveys help identify conditions indicating the potential for an economically recoverable mineral deposit.
The Abandoned Hardrock Mine Reclamation (AHMR) Program enhances public safety and improves water, soil, and air quality by reducing or eliminating the effects of past hardrock mining (such as gold, silver, lead, and uranium) across the United States through reclamation and remediation of abandoned mine lands (AMLs).
The average Hard Rock Miner salary in the United States is $52,577 per year or $25 per hour. Hard rock miner salaries range between $25,000 and $107,000 per year.
Typically, long hole mining requires two excavations within the ore at different elevations below surface, (15 m – 30 m apart). Holes are drilled between the two excavations and loaded with explosives.The holes are blasted and the ore is removed from the bottom excavation.
First the quartz had to be blasted from the bedrock schist, in tunnels of underground mines. Ore was crushed in water to a fine slurry in large stamping batteries. The gold liberated at this stage was then dissolved in mercury or cyanide and extracted.
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