Mining of Iron Ores
Mining of Iron Ores
The chemical element iron is the fourth most common element in the Earth’s crust and the second most abundant metal. About 5 % of the Earth’s crust is composed of iron. The metal is chemically active and is found in nature combined with other elements in rocks and soils. In its natural state, iron is chemically bonded with oxygen, water, carbon dioxide, or sulphur in a variety of minerals. An ore is a material which occurs naturally and which contains a mineral(s) that can be extracted for a profit. Iron ore occurs naturally in a variety of forms, from sand-like iron fines to solid rock masses.
Iron is averaging from 2 % to 3 % in sedimentary rocks to 8.5 % in basalt and gabbro (a coarse-grained igneous rock which is relatively low in silica and rich in iron, magnesium, and calcium) in the earth’s crust. Since iron is present in several areas, it is of relatively low value and hence, a deposit is required to have a high percentage of metal to be considered ore grade. Typically, a deposit is to contain at least 25 % iron to be considered economically recoverable. This percentage can be lower, however, if the ore exists in a large deposit and can be concentrated and transported inexpensively.
Over 300 minerals contain iron but the primary sources of iron-ore minerals are(i) magnetite (Fe3O4), (ii) hematite (Fe2O3), (iii) goethite (Fe2O3.H2O), (iv) Limonite (Fe2O3.H2O), (v) siderite (FeCO3), and (vi) pyrite (FeS2). Hematite and goethite ores are most desirable because of their high iron content and ease of processing. Magnetite ore is increasingly being mined as more preferable deposits are becoming scarcer. Other less common iron-bearing minerals include pyrite, siderite, and titano-magnetite in mineral sand resources in some countries (e.g., iron sand in New Zealand). In terms of mining, out of six significant iron-containing mineral deposit types, only the first three are normally considered to be viable for mining. The most important iron ore-forming minerals areas given below.
Magnetite – Magnetite forms magnetic black iron ore.
Hematite – Hematite is a red iron ore. Hematite occurs in almost all forms, from solid rock to loose-earth. It is the most plentiful iron ore and occurs in large quantities throughout the world.
Goethite – Goethite (Fe2O3.H2O), a brown ore, contains iron.
Limonite – Limonite (Fe2O3.H2O) is a yellow-brown iron ore. Limonite is a collective term for impure goethite and a mixture of hydrated iron oxides.
Taconite ore contains low-grade iron in fine specks and bands. It is an extremely hard and flinty which contains around 17 % to 30 % iron. The iron in taconite occurs principally as magnetite and hematite and finely dispersed with silica in sedimentary deposits. The mining of taconite, a tough and abrasive low-grade ore (ranging from 40 % to 60 % silica and 17 % to 30 % iron), is especially difficult because of the extreme hardness of the ore. Because of this hardness, additional drilling, blasting, crushing, and grinding are frequently needed to extract the ore.
Most of the mineral resources of iron ore are not easily found and do not come out of the ground in a useable form. Finding these resources, obtaining (mining) them, and processing them into something useable takes several varied and frequently technologically advanced steps. The typical steps in recovering a mineral resource and converting it to a useable state include (i) locating it (exploration), (ii) obtaining it (extraction or mining), (iii) concentrating it (beneficiation), and (iv) cleaning up during / afterward (remediation / reclamation / mine closure). Mining of metal ores is an important step. Every step of the mineral extraction process is very complex.
The process of mining starts with the discovery of an iron ore deposit through extraction of iron ore and finally to returning the land to its natural state. It consists of several distinct steps. The first is discovery of the iron ore deposit which is carried out through prospecting or exploration to find and then define the extent, location, and value of the ore body. This leads to a mathematical resource estimation of the size and grade of the deposit. Exploration and evaluation consist of identification and quantification of ore bodies by using a range of geological, geophysical, and metallurgical techniques. In its simplest forms exploration involves drilling in remote areas to sample areas. The data from exploration activities is logged, mapped, analyzed, and interpreted frequently by using models.
After the ore body has been evaluated, a detailed plan for mining is developed. This detailed plan identifies which ore bodies are to be mined and in what sequence in order to deliver the required iron ore product at an appropriate cost. The process of mine planning is an important step before the start of mine development and it continues on day-to-day basis once the mine becomes operational. To gain access to the iron ore deposit within an area, it is frequently necessary to mine through or remove waste material (also known as overburden) which is not of an interest. The total movement of ore and waste constitutes the mining process. Frequently, more waste than ore is mined during the life of a mine, depending on the nature and location of the ore deposit. Removal and placement of overburden is a major cost in the mining operation.
Mining is actually a very expensive process, so mining organizations invest time and money to make sure they have picked a good location. In the exploration part of the process, there are normally multiple locations being explored and it can take a number of years to determine which of the sites are viable. Some sites deemed unfit for development can become more appealing in the future if technologies change and / or the price of the ore rises.
Although not all ore bodies outcrop at the surface, some will. It is very important to determine not only the surface location (outcrop) of an ore, but also to figure out the size, depth, and orientation (trend) of the deposit. By just looking at the surface outcrop, it is impossible to tell the size and shape of the underground ore body. Fig 1 shows examples of how a deposit can extend below the surface of the Earth surface when looking at a surface exposure.
Fig 1 Examples of how a deposit can extend below the surface of the Earth surface when looking at a surface exposure
Estimates of the quantities of elements in the Earth’s crust represent averages over the entire crust and seldom reflect the composition at a particular location. Rocks and minerals, and hence elements and compounds, are concentrated in certain locations because of rock-forming processes which have occurred in the past and / or are occurring today. During the exploration process, a mining organization seeks an area where the desired mineral resource is concentrated and attempts to determine the size of the ore body and the ore grade of mineral resource. Higher ore grades (higher concentrations) make the mining operation more viable.
However, there are several other factors which can influence the decision to extract an ore from a specific area. These can include the shape and depth of the ore body, the available mining technology, the potential environmental impact, the need and availability of water, access to workers, proximity to transportation and consumers, local, national, and other statutory regulations, politics and / or political boundaries, social norms, and human health concerns. During the exploration process, geo-scientists use several methods to find suitable locations and determine the depth and shape of the ore body. These include the following.
The first is creating and reviewing geological maps. Geological maps show the locations of different types of bedrock (bedrock is the rock which is closest to the surface), give exploration geologists hints as to what geological processes acted in a given area and suggest how rocks are distributed at depth. Maps help geologists compare an area with other sites which have yielded highly concentrated ores in the past.
The second is visiting a potential mine site and completing field studies, which can entail additional geological mapping, surface rock sampling, and / or chemical analyses of rock, soil, and water samples.
The third is performing ‘non-invasive’ studies to obtain underground information. These studies are similar to someone using a metal detector to find discarded coins on a beach. The larger-scale geophysical studies used by mining organizations can include seismic, gravity, magnetic, or other surveys.
The fourth is drilling down through the surface to obtain samples at depth. Hollow drills are used that bring cores (long cylinders of rock) to the surface.
Once an appropriate site is located, the mining organization obtains any necessary clearances, permits, and leases, etc. Then the extraction process can begin.
Extraction or mining
There are two basic methods of mining iron ore. These are (i) surface mining or open-pit mining, and (ii) underground or shaft mining. Iron is mined almost exclusively in surface operations. However, there are presently a few operating underground iron mines. The decision to employ underground or surface mining techniques is dependent on the proximity of the ore body to the surface. To be competitive, iron mining is to be done on a very large scale. Surface mining is the preferred choice, although there are exceptions. Majority of the mines are iron ore production complexes and virtually all the ore is processed before shipment. Small, and low-capacity mines are rare.
A single mine can employ both methods. Prior to 1900, underground mining was the most common method in some countries. Surface mining is now more common, because of the development of equipment which can easily move large quantities of rock at the earth surface. The large quantity of rock which is broken up during mining that does not contain enough of the mineral resource to process the rock further is called waste rock.
The mining method selected depends on a variety of factors, including the nature and location of the deposit and the size, depth, and grade of the deposit. Underground mining requires more energy than surface mining because of the higher requirements for hauling, ventilation, water pumping, and other operations. Surface mining accounts for the majority of iron ore being produced worldwide.
On the basis of mining methods, iron ore mining can be broadly divided into two categories namely manual mining and mechanized mining. Large iron ore mines are mechanized mines while manual mining methods are employed in the small mines.
Manual mining method is normally limited to float ores. Mining of reef ore is also being done manually on a small scale. The float ore area is dug up manually with picks, crow bars, and spades, and then the material is manually screened to separate + 10 mm float ore which is then stacked up. The waste is thrown back into the pits. As regards to the reef ores, holes of 0.6 m deep and 30 mm to 40 mm diameters are drilled with hand held jack-hammers operated with portable compressors. These holes are with a spacing of about 0.6 m and each hole is charged with 150 grams to 200 grams of gun powder or gelatin cartridges. The blasted broken ore is manually screened, stacked for loading in dumpers for dispatch.
Most of the large iron ore mines are mechanized mines. In these mines, mining is done to extract iron ore from surface deposits. In these mines. all the operations are mechanized and mining is invariably done through systematic formation of benches by drilling and blasting.
Surface mining – Surface mining methods are designed for extracting ore from surface deposits. The largest mines are normally surface mines. Heavy machinery and blasting procedures are used to remove large quantities of surface rock, which considerably disturbs the land. A typical surface mine can produce up to 150,000 tons of ore every day. Sometimes whole mountains (or tops of mountains) are removed through surface mining processes. The most predominant surface mining methods used to extract iron ore are open-pit and open-cut methods. These two methods are considered to be the least expensive extraction techniques. The recovery of material is normally done from an open pit in the ground.
After the soil and overlying rock are cleared, the ore is drilled and the holes are loaded with explosive mixtures for blasting. The wide holes in the ground created by drilling, blasting, and ore removal are referred to as open pits. Areas for open pit mining are selected using the mining plan. Identified areas are then tagged. The ore is mined from large open pits by progressive extraction along steps or benches. The benches provide access to progressively deeper ore, as upper level is removed. Drilling in the benches of open pit mining is done for production of iron ore with mechanized drills specific for each mining method.
When the iron ore lies close to the surface, it frequently can be uncovered by stripping away a layer of dirt, sometimes only a metre or two thick. The ore is mined from large open pits by progressive extraction along steps or benches. The benches provide access to progressively deeper ore, as upper-level ore is removed.
Overburden consisting of surface vegetation, soil, and rock material, is removed (stripped) to reach buried ore deposits. Overburden is continually removed during the life of the mine as the high wall is cut back to permit deepening of the pit. Overburden and stripping ratios are important in determining whether a deposit is to be mined. The stripping ratio describes the unit of overburden which is to be removed for each unit of crude ore mined. Stripping ratios increase with the quality of the ore being mined and cost factors related to processing and transportation. These ratios can be as high as 7:1 (for high-grade wash ores) or as low as 0.5:1 (for low-grade taconite ores). Fig 2 shows a typical surface iron ore mine.
Fig 2 Typical surface iron ore mine
In the process of mining ore benches are developed for the purpose of drilling, blasting, and hauling of the ore to the crushing plant. The height of the benches is dependent on several factors such as output requirement, shape, size and depth of occurrence of ore body, geological disturbance suffered by the ore body, hardness and compactness of the ore body, type and the size of deployed for the mining operations etc. The length of the face is dependent on different factors such as contours of deposit, output needed, variation in grade, blending requirements, and capacity of loading machinery etc. The width of the bench is governed to a large extent by the size of the largest machinery deployed.
After the soil and overlying rock are cleared, the ore is drilled. The portion of the ore body to be removed is first drilled by using rigs in an appropriate pattern. The main objective of drilling operations is to create a hole of suitable diameter, depth, and direction in rock for explosives to be placed for blasting activities. The drilling of the holes is done normally in a particular pattern which depends on the bench height, the diameter of the hole, the drilling machinery deployed, nature of rock, and the types of explosives used. The blast holes are normally vertical but can be inclined for obtaining better blasting results.
Production drilling is conducted with mechanized drills, specific for each mining method. The primary objective of drilling operations is to create a hole of suitable diameter, depth, and direction in rock for explosives to be placed for blasting activities. At facilities operating in colder environments, salt brine can be added to drilling fluids to prevent freezing of the material in permanently frozen host rock.
The object of blasting is to expose the ore body for extraction or to create adits (a horizontal passage leading into a mine for the purposes of access or drainage). Blasting is also used to break up ore in surface mining operations. The main requirement for an explosive to be used in mine is the ability to achieve complete combustion without an external oxygen supply. In the past, explosives used in blasting were comprised of nitro-glycerine, carbonaceous material, and an oxidizing agent. However, these days, the most common explosives used are mixture of ammonium nitrate and fuel oil (ANFO).
The explosives are detonated by a high explosive blasting cap and / or primer. Now a days nonel (non-electric) is used as detonator. Nonel is shock tube detonator designed to initiate explosions. Instead of electric wires, a hollow plastic tube delivers the firing impulse to the detonator, making it immune to most of the hazards associated with stray electrical current. It consists of a small diameter, three-layer plastic tube coated on the innermost wall with a reactive explosive compound, which, when ignited, propagates a low energy signal, similar to a dust explosion. The reaction travels at approximately 2,000 metre per second along the length of the tubing with minimal disturbance outside of the tube. The design of nonel detonators incorporates patented technology, including the cushion disk (CD) and delay ignition buffer (DIB) to provide reliability and accuracy in all blasting applications
Materials generated as a result of open-pit mining include overburden, waste rock, and mine water containing suspended solids and dissolved materials. Other wastes can include small quantities of oil and grease spilled during extraction. Mine water contains dissolved or suspended constituents similar to those found in the ore body itself. These can include traces of aluminum, antimony, arsenic, beryllium, cadmium, chromium, copper, manganese, nickel, selenium, silver, sulphur, titanium, and zinc.
Blasting uses explosives to aid in the extraction or removal of to be mined material by fracturing rock and ore using the energy released during the blast. The energy consumed in the blasting process is derived from the chemical energy contained in the blasting agents. This sets blasting apart from other processes, which are powered by traditional energy sources, such as electricity and diesel fuel. A common explosive used for blasting operations is ammonium nitrate / fuel oil (ANFO) mixture. The powder factor is the quantity of explosives used per unit of rock blasted and varies depending on the rock type and strength. The explosive is detonated with a nonel (non-electric) device for firing. Blasting reduces the size of ore before it undergoes crushing and grinding, thereby reducing the energy consumption of crushing and grinding processes. Hence, optimizing blasting techniques produce downstream energy savings.
Following blasting, the fractured ore which is produced in known as crude ore or ‘run of mine’ (ROM) ore. Crude ore is loaded by huge electrical shovels, hydraulic excavators, or front-end loaders onto large dump trucks. In open-pit mines, the broken rocks are normally excavated by a front-end loader and loaded onto a dump truck for haulage to the processing plant. Majority of the mines have a loading fleet including wheel loaders, shovel units, and excavators. The wheel loaders have a capacity ranging from 50 tons (t) to 90 t, while the shovel units and excavators have capacities ranging from 200 t to 250 t. The haulage units typically include off-road dump trucks with carrying capacities ranging from 150 t to 300 t of rocks. Typical numbers of these haul trucks can be from 10 to 22 depending on the mine size.
Majority of the equipment used in the transfer or haulage of materials in mining is powered by diesel engines. Diesel technologies are highly energy-intensive, accounting for 87 % of the total energy consumed in materials handling.
Underground mining – Historically, underground mining methods, including caving and stopping, were commonly used to extract iron ores. Underground mining includes the use of tunnels or vertical shafts to obtain ore from below Earth’s surface. These shafts can penetrate down into the ground or sideways into a mountain side. Underground mines tend to be smaller operations than surface mines, generating a few 100,000 tons to a million tons of ore over the life-time of the mine. Normally, less land is disturbed in underground mining as compared to surface mining.
Underground mines are established in areas with promising ore deposits. Iron ore deposits can lie deep underground. A shaft is dug from the surface and an elevator or hoist is installed. The shaft is the primary vertical channel through which people and ore are transported in and out of the mine. It can be desirable to sink a vertical shaft in barren wall rock at one end or to one side of the ore deposit to keep haulage and hoisting facilities clear of actual underground mining while minimizing haulage of ore underground to the mine exit. The elevator of the mine is called a cage and the ore reaches the surface through a car called a skip.
A ventilation system near the main shaft ensures that miners receive fresh air and prevents the accumulation of dangerous gases. Miners cut tunnels (drifts) branching out from the shaft at various levels to access the veins of ore. These levels are, in turn, connected by openings called raises. Stopes are the chambers in which ore is broken and mined. Cars or other conveyors carry the ore to the shaft, where it is hoisted to the surface.
The basic mine plant for underground mining operations consists of head-frame, hoist, timber framing and storage area, change house of miner, compressor house, machine shops, warehouse, office, ore storage, ore loading, and shipping facilities.
Processing of crude ore
Following blasting, the fragmented (crude) ore is loaded for transport by shovels, excavators or front-end loaders onto large dump trucks for its transportation to the Ore processing (normally crushing and washing) plant. The transportation is facilitated by maintaining mine haul roads. Over-land belt conveyors are used to transport the crude ore material where there are long distances between the pits and crushing plants and between the crushing plants and loading sites.
Crude ore, or ROM ore which is mined in the natural state, seldom occurs in a pure state and needs some form of processing. Concentrations of as little as 30 % can be of commercial interest, provided other factors such as gangue content, the size of the deposit, and accessibility are favourable.
Crude ore normally has with it other minerals (gangue), which reduce the iron content. In crushing and washing plants the processing of the crude ore is carried out. Processing of the ore ranges from simple crushing and screening and separating various size fractions of the ore to the processes which beneficiate or upgrade the quality of the iron ore products. This is done by physical processes, which remove impurities by difference in particle density, or size gravity, or size separation. Processing can be wet or dry. Further ore handling, washing, and screening operations are mechanized in the crushing and washing plants.
Crushing is the process of reducing the size of crude ore into coarse particles (typically coarser than 5 mm). Depending on the ore characteristics, the crushing of crude ore can be single stage (primary) crushing, double stage (secondary) crushing, or triple stage (tertiary) crushing. The efficiency of crushing depends on the efficiency of upstream processes (rock fragmentation because of blasting or digging in the extraction process) and, in turn, has a significant effect on downstream processes (grinding or separations).
In some cases, the primary crushing located in the mine, while the secondary crushing or tertiary crushing are located at the steel plant. The primary crushing stage reduces the very large size of crude iron ore to around 150 mm and further down in subsequent crushing stages to the size of calibrated iron ore (-40 mm to +10 mm), CLO, as the final product. The crusher product is fed to the milling operation for further size reduction when subsequent processing of ore is needed.
Screening is an important step for dry beneficiation of iron ore. Crushing and screening is typically the first step of iron ore beneficiation processes. In most ores, including iron ore, valuable minerals are normally intergrown with gangue minerals, so the minerals need to be separated in order to be liberated. This screening is an essential step prior to their separation into ore product and waste rock. Secondary crushing and screening can result in further classification and grading of iron ore. The fines fraction is normally of lower grade compared with lump ore.
The iron ore processing can be (i) dry processing, (ii) dry cum wet processing, and (iii) wet processing. Dry processing (Fig 3a) is done to meet the size requirements and involve multi-stage crushing and screening to meet the size requirements needed by different iron smelting processes. In dry-cum-wet process (Fig 3b), fines fraction (-10 mm) generated after dry processing is further processed in mechanical classifiers, and hydro-cyclones etc. to obtained -10 mm to + 0.15 mm size product which constitutes the feed for sintering. The classifier / hydro-cyclone overflow i.e., -0.15 mm (100 mesh) size product constitutes the slime and dumped into the tailing pond. Fig 3 shows dry and dry-cum wet processing of ores.
Fig 3 Types of processing ores
The wet processing (Fig 4) is normally practiced for low / medium grade (60 % to 63 % Fe) hematite iron ore. The wet process consists of multi-stage crushing followed by different stages of washing in the form of scrubbing and / or screening, classification etc., but the advantage is only partial removal of adhered alumina and free silica in the calibrated lump ore shaving size fraction of -40 mm to +10 mm. The classifier underflow (-10 mm to + 0.15 mm) is directly used for sinter making, while classifier overflow (100 mesh) is dumped in the tailing pond. This washing process marginally improves the handling properties of the ore because of the removal of the clayey material. Fig 4 shows wet processing of ore.
Fig 4 Wet processing of ore
The processed ore is then sent for stacking and stockpiling. The processed ore is stockpiled and blended to meet product quality requirements. Stackers are used for stockpiling so that bulk goods can later be reclaimed by reclaimers for loading onto a dumper truck or railway wagons for transporting to another stock-pile in the steel plant or port for ship-loading. Iron ores are transported from the mine site to the steel plant or port for export normally by either railway wagons or dumper trucks. The ore which is despatched from the mine site after dry or wet processing is known as direct shipping ore.
On mine sites, there are other equipments used for road construction, maintenance, and dust suppression within the mine site, such as dozers, graders, excavators, and water tankers.
Potential issues related with mines
The mining industry provides raw materials for the production of iron and steel products needed by the society. It provides jobs (directly and indirectly tied to the mine), pushes technology forward, and plays a key role in local and global economic systems. In spite of these benefits, mining of the ore poses several environmental issues.
Waste materials generated as a result of open pit mining include overburden, waste rock, and mine water containing suspended solids and dissolved materials. Other waste materials can include small quantities of oil and grease spilled during extraction. Mine water contains dissolved or suspended constituents similar to those found in the ore body itself. These can include traces of aluminum, antimony, arsenic, beryllium, cadmium, chromium, copper manganese, nickel, selenium, silver, sulphur, titanium and zinc etc.
The first issue related to the mining operation is the generation of the waste rock. Waste rock can include the non-ore containing rock on top of the ore body (overburden) and the rock which contains ore that is not concentrated enough to mine. In surface mining, around 2 tons to 3 tons of waste rock (depending on the nature of the ore deposit) is removed for each ton of ore. Underground mining normally creates less waste rock than surface mining since the waste rock is either moved to the surface or used to fill in areas of the mine no longer in use. Piles of waste rock normally deposited close to the mine. These piles can cover huge land area and have substantial height (piles can have even a height of 30 metres).
Mining increases both rates of weathering and erosion. Since the digging and blasting break rock into smaller pieces (mechanical weathering), waste rock has more surface area exposed to chemical weathering. For some mining wastes, this is only a small problem. However, some waste rock creates hazardous conditions when chemical weathering mobilizes metals or other undesirable chemicals.
These undesirable chemicals can make stream or groundwater more highly acidic. The acidic (low pH) water can be harmful to local organisms, and several of the mobilized metals are toxic to humans, plants, and animals.
Responsible mining operations carefully plan the placement and layering of waste rock, and monitor water flow through waste piles in order to minimize waste rock issues. Statutory regulations are also there for controlling this issue.
The second issue is the tailings which is the waste product for the wet processing. The tailings are normally pumped downhill into impoundments called tailings ponds. Tailings ponds can have large areas with substantial depth. If one of the walls / dams of the impoundment breaks, then a lot of contamination can be released very quickly. Additionally, if a tailing pond dries out, the metals can be transported as dust on the wind and hence have the potential to be inhaled by nearby residents.
A leaky tailings pile is especially problematic since sulphide minerals, frequently found in association with metal ores, can occur in high concentrations within the tailings. When exposed to oxygen, sulphide minerals can form sulphuric acid and lead to the development of acidic soils and waters. This can influence water quality in the area by making the it highly acidic or by an increase in dissolved (and undesirable) metals which results from this acidity (sulphide minerals can be the ones to cause problems in waste rock as well).
Preparing for mine closure
Once the ore material runs out, or becomes technologically or economically inaccessible, the mine is to be closed. In places where water has been continually pumped out to keep mining operations dry, the closed mine gets fill with water. This water pool is the cause of several environmental issues, such as acid mine-drainage. Mines operating in several countries are to meet high standards. These mines are required to provide some amount of environmental and human health protection while they are in operation and enact a plan to limit environmental and human health issues well after the mine closes. For example, while the mining is still happening, the mining organization is required to plan how it grades slopes to decrease erosion and make slopes more stable once they close the mine.
Reclamation is the restoration of land to either natural conditions or another useful purpose. it frequently involves the process of stabilizing soils and slopes in an area through grading (creating a different, gentler slope) and planting trees and plants. Normally the addition of new soil, or treatment of the existing soil, is necessary prior to revegetation. This step can be started before the mine is fully closed. Reclamation can occur as sections close (either parts of the surface mine or the waste rock piles). This can also help improve the aesthetics of the mine area while it is still open.
Remediation is the process of fixing, removing, or counter-acting an environmental issue, In mining, the water leaving the mine area (waste rock, tailings ponds, leach piles, or from the mine itself) frequently is to be treated (remediated) before being released back into the natural system. Like reclamation, treatment of acidic or otherwise contaminated water does not need to wait until the mine closes but is to be part of the mining plan and be done as mining happens.
Since the late 1960s, several countries have enacted statutory regulations in the interest of protecting human health and the environment. A number of these acts directly or indirectly regulate the mining industry. These regulations have become much more stringent since the 1970s. However, there are still environmental and health issues related to mining which include (i) the use of water, especially in arid environments where water is scarce, (ii) the impact on forests and eco-systems, including habitat destruction or alteration, (iii) contamination of water through acid mine drainage, and accidental spills, etc., (iv) mine worker health and safety, although this has been improved through statutory regulations, (v) unsafe practices when mines do not meet the statutory regulations, (vi) the use of public lands, such as in National Forests, for mineral extraction, and (iii) ground subsidence above underground mines.