SUSTAINABLE MINING
Major Types of Minerals Found in the World
Explain major types of minerals found in the world
So far over 4600 minerals have been found and every year new ones are discovered. Only 100 of these are common, while the rest are either encountered occasionally, or are very rare. With such a large number of minerals, it is difficult to identify and classify them separately. However, mineralogists identify minerals based on a number of characteristics which include streak, lustre, sheen, hardness, cleavage, crystal system, colour, specific gravity, clarity or transparency.
All minerals are formed from one or more of eight main elements. These are: oxygen, silicon, potassium, sodium, calcium, magnesium, iron and aluminium. Minerals are divided into two broad groups, based on their composition, as either silicate or no-silicate minerals.
Silicate Minerals
The most commonly found group of minerals in the Earth's crust is the silicate group. Almost all silicate minerals have silicon and oxygen as their basic units. Most silicate minerals are formed by the cooling of molten rocks. As the molten rocks come closer to the surface inside the Earth's crust, they start cooling very fast and combine with the most abundant element in the Earth's crust–silicon. Silicate minerals constitute approximately 90% of the Earth's crust. Mica, quartz, amazonite, olivine, and biotite are some examples of silicate minerals.
Examples of silicate minerals are as shown in the table below.
| Mineral | Chemical formula | Type of rocks that they are commonly found within | How People Use Them |
| Olivine | (Mg, Fe)2SiO4 | Ultramafic igneous rocks | A gemstone! |
| Pyroxene group | (Mg, Fe)SiO2 | Basaltic igneous rocks | - |
| Amphibole group (example: hornblende) | (Ca2Mg5)Si8O22(OH)2 | Andesitic igneous rocks | - |
| Micas | Biotite: K(Mg, Fe)3Si3O10(OH)2 Muscovite: KAl3Si3O10(OH)2 | Andesitic igneous rocks | Colonial Americans used sheets of mica as window glass. |
| Feldspars | Orthoclase: KAlSi3O8Plagioclase: (Ca, Na)AlSi3O8 | Granitic igneous rocks | Important for making ceramics and glass |
| Quartz | SiO2 | Granitic igneous rocks | Quartz is the raw material for glass and helps clocks keep time. |
Non-silicate Minerals
There is a complete range of non-silicate minerals. Some of these are formed when there is cooling of magma, while others are formed when water in them evaporates, or due to mineral decomposition. The non-silicates can be further classified into different groups which are:
Native elements: Many pure elements that are found with a distinct mineral structure and occur naturally in an uncombined form fall under this category. For example, uncombined carbon is often found in its pure state in the form of graphite or more rarely as diamond. Gold, silver, and sulphur are other elements, which are also found in their pure state. Even though these are pure elements, they qualify to be known as minerals, but no further chemical process is required on them.
Sulphides: This class of minerals have sulphide (S2−) as their basic unit. These inorganic compounds are sometimes as economically important as other ores. Some examples include Nickeline (NiAs), Pyrite (FeS2) and Molybdenite (MoS2).
Oxides: When an ore is found in which one or more elements are combined with oxygen, it is an oxide mineral. These may have chemical formulas of the type XO (MgO, ZnO, CuO, etc.), X2O (Cu2O), X2O3 (Al2O3, Fe2O3), XO2 (MnO2, SnO2) and XY2O4 (MgAl2O4, FeCr2O4). The oxide minerals are mostly of metallic elements. Example: haematite, magnetite, and cuprite. Silicates and oxides are the most common types of minerals in volcanoes, especially after an eruption.
Carbonates: This particular type is formed when a single carbonate ion (CO32-) reacts with a metal ion of complementing polarity. Example: siderite (FeCO3), smithsonite (ZnCO3), calcite (CaCO3). Carbonate minerals are used in making cement and other bonding material.
Sulfates: The mineral class which includes the sulphate ion (SO42-) within its molecular structure is categorized as a sulphate mineral. Minerals like Gypsum (CaSO4·2H2O) and Barite (BaSO4) are examples of sulphate minerals.
Organic Minerals: This class of minerals includes biogenic substances, genesis, or origin of which can be attributed to a geological process. Organic minerals include all types of oxalates, mellitates, citrates, cyanates, acetates, formates, hydrocarbons, etc
Apart from these, there are many more non-silicate minerals, like nitrates, sulphides, phosphates, etc., but most of the 4,000-odd listed minerals are grouped in the above categories. Make sure you do not get confused between minerals and rocks. A rock is a combination of a number of minerals, which may also include organic remains and mineraloids, i.e., non-crystalline minerals
Specific examples of non-silicate minerals are shown in the table below.
Common Non-silicate Mineral Groups
| Mineral Group | Example of Mineral | How People Use Them |
| Oxides | Hematite (Fe2O3) (Magnetite is another type of oxide!) | Ore of iron |
| Sulphides | Pyrite (FeS2) | An ore of iron. Also known as fool’s gold. |
| Sulphates | Gypsum (CaSO4 (+2H2O)) | Used to make plaster |
| Halides | Halite (NaCl) | Table salt |
| Carbonates | Calcite (CaCO3) | Used to make cement |
| Native Elements | Sulphur (S) | An ingredient of drugs and chemicals |
Mining Regions in the World Map and the Type of Minerals Extracted
Locate mining regions in the world map and the type of minerals extracted
A world map showing distribution of major minerals
Coal
Throughout history, coal has been used as an energy resource, primarily burned for the production of electricity or heat. It is also used for industrial purposes such as refining of metals. Coal is the largest source of energy for the generation of electricity worldwide, as well as the largest worldwide source of carbon dioxide release into the atmosphere.
Coal is today used to heat furnaces, for domestic heating and for the generation of thermal electricity.China is the largest producer of coal in the world. The USA contains the world’s largest coal reserves, followed by Pakistan, Russia, China and India. China and the USA are also among the largest consumers of coal.
World coal production and consumption
In USA, the states with largest coal reserves are, in descending order, Wyoming, West Virginia, Illinois, and Montana. The largest single mine in USA is the North Antelope Rachele, which produces over 100 million tones coal annually.
The Ruhr coalfield in Germany is one of the largest coal reserves. In Tanzania, there are coal deposits at Mchuchuma (Njombe region) and Kiwira (Mbeya region).
Petroleum
Petroleum is mainly used as fuel to power machines such as vehicles. It is also used as a source of heat and heating. Petroleum occurs as crude oil which is then refined to obtain fractions with varied uses. These fractions include diesel, petrol, paraffin (kerosene), jet fuel and lubricants.
Some of the leading petroleum producers are Saudi Arabia, Russia, Iran, Iraq, Nigeria, United Arab Emirates, Angola, Venezuela, Kuwait and Libya.
In Saudi Arabia the oilfields are located in such areas as Abqaiq, Ghawar, Khurais, Qatif, Safaniya and Shaybah. In Nigeria, oil wells are found in the Niger Delta.
Diamond
Diamond is the hardest and most coveted of all the precious stones. Due to its extreme hardness, it is used to make glass cutters, drilling devices, rock borers, and as an abrasive for smoothing very hard materials. Polished diamond is used to make jewellery such as necklaces, rings and bracelets.
The major world producers of diamond include Russia, Botswana, DRC, Australia, South Africa, Canada, Angola, Namibia, Ghana and Brazil. In Tanzania, diamond is mined at Mwadui in Shinyanga region.
Copper
Copper is a major metal and an essential element used by man. It is found in ore deposits around the world. It is also the oldest metal known to man and was used many years ago.Today, the functions of copper have expanded to include heating, cooling and refrigeration, electrical wiring, generation and transmission of electrical power, automotive applications, and many more.Some of the major copper-producing countries in the world are Chile, USA, Peru, China, Australia and Zambia.
In Zambia, copper is mined at Kitwe and Konkola. Zambia is internationally recognised as a major producer of copper and cobalt. It is ranked the word’s seventh producer of copper and the word’s second-largest producer of cobalt after the DRC.
Gold
Gold is the most popular and well known mineral, known for its value and special properties since the earliest time. Gold has its use in jewellery, electronics and computers, dentistry and medicine, aerospace, and medals and awards. Some of the leading producers of gold in the word are China, Australia, USA, Russia, South Africa and Ghana.
Tanzania has become one of the fastest-emerging gold producers in Africa, and is now the continent’s third largest producer after South Africa and Ghana. Of late there are nine gold mines in Tanzania namely, Bulyanhulu, Buckreef, Geita, Golden Pride, Golden Ridge, North Mara, Tulawaka and Kitongo.
Iron ores
Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides. The iron itself is found in the magnetite (72.4% iron), haematite (69.9% iron), goethite, (62.9% iron), siderite (48.2% iron) and limonite ores.
Ores carrying very high quantities of iron, haematite or magnetite (greater than 60% iron) are knows as “natural ores”.The leading iron producers in the world are China, Australia, Brazil, India, Russia, Ukraine, South Africa and USA.
Bauxite
Bauxite, an aluminium ore, is the world’s main source of aluminium. The ore contains about 98% of aluminium oxide.
Australia is the top producer of bauxite with almost one-third of the world’s production, followed by China, Brazil, Indonesia, India, Guinea and Jamaica. Although aluminium demand is rapidly increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminium for many centuries.
Various Ways of Mining
Categories of various ways of mining
Mining methods have drastically transformed over many years. Technological advances have seen improvement in efficiency, safety and health of miners. Also the impacts of mining operations to the environment have been greatly minimized.
To gain access to mineral deposits within an area, it is often necessary to mine through or remove the waste material (overburden) which is not of immediate interest to the miner. The total movement of ore and waste constitutes the mining process.
There are several methods of mining which depend on the type of a mineral and whether the mineral is located close or deep in the earth’s crust.
The following are the main mining methods:
Surface mining
This is done by removing (stripping) surface vegetation, dirt, and if necessary, layers of bed rock in order to reach buried ore deposits. Techniques of surface mining include the following:
- Open pit mining:This is method is also knows as opencast mining or open cut mining. It involves extracting rock or minerals from an open pit or burrow.
- Quarrying:This is the process which involves excavating stone, rock, construction aggregate, riprap, sand, gravel or slate from the ground. Continuous excavation of these minerals from the earth results to an open pit called a quarry.Note: A quarry is the same thing as an open pit mine from which minerals are excavated. The only trivial difference between the two is that open pit mines that produce building materials and stones are commonly referred to as quarries.
- Stripping:This consists of removing surface layers off to reveal ores or seams underneath.
- Mountaintop removal:This technique, commonly associated with coal mining involves taking the top of a mountain off to reach ore deposits at depth.
- Landfill mining:A process whereby solid wastes which have previously been land-filled are excavated and processed.
Mountaintop Removal Mining
Underground (sub-surface) mining
Underground mining consist of digging tunnels or shafts into the earth to reach buried deposits. The ore, for processing, and waste rock, for disposal, are brought to the surface through the tunnels and shafts. Techniques of underground mining include the following:
Drift mining – This technique utilizes horizontal access tunnels. Sometimes the mineral occurs in the side of a hill or valley. In such cases, a horizontal or nearly horizontal tunnel is dug into the side of a hill or valley until the mineral is reached. This horizontal tunnel is called an adit. The audit serves as an entrance to an underground mine by which the mine can be entered, drained of water, ventilated and mineral extracted.
Horse level Adit in the abandoned lead mine, Nenthead, County Durham, UK
If the mineral is petroleum or natural gas, the deposit is reached by sinking wells. Pumping or own pressure brings the gas or petroleum to the surface.
Other minerals are extracted by digging shafts to reach the mineral-containing layer. Hot water is then pumped in to dissolve the mineral and the mixture is pumped out. The water is ultimately evaporated, leaving the mineral behind. Sulphur is one of the minerals extracted by this method.
Slope mining: This technique, unlike drift mining, uses diagonally-slopping access shafts (tunnels).
Shaft mining: This one utilises vertical access shafts.
Alluvial or placer mining
Placer mining is the mining of alluvial deposits for minerals. This may be done by open pit (open-cast) mining or other means. The placer mining is frequently used for precious metal deposits (particularly gold) and gemstones, both of which are often found in alluvial deposits (deposits of sand and gravel in stream beds or glacial deposits). Since gems and heavy metals, like gold, are denser than sand, they tend to accumulate at the base of placer deposits.
The placer mining technique involves digging out the alluvial deposit from the river bed, mixing it with water, and then swirling (rotating) the mixture around with water in a shallow pan. During swirling, the pan is tilted in such a way that the lighter sand or gravel is washed over the side, leaving Horse level Adit in the abandoned lead mine, Nenthead, County Durham, UK the heavier mineral at the bottom of the pan. This technique is used in gold mining by small scale gold miners in Tanzania and South Africa.
Ways of Processing Different Types of Minerals
Explain ways of processing different types of minerals
Once the mineral ore has been excavated from the ground it has to be treated in various ways to separate the required mineral from the waste material and impurities. The process of treating crude ores and mineral products in order to separate the valuable minerals from the waste rock or gangue is called mineral processing.
Depending on the chemical composition of the ore, mineral processing can involve the following general operations:
Comminution
Comminution is particle size reduction of materials. Comminution may be carried out on either dry materials or slurries. Crushing and grinding are the two primary comminution processes. Crushing is normally carried out on the raw ore, while grinding (normally carried out after crushing) may be conducted on dry or slurried material.
Sizing
Sizing is the general term for separation of particles according to their size. The simplest sizing process is screening, or passing the particles to be sized through a screen or number of screens. The screening equipment can include various types of screens or wire mesh. Screens can be static (typically the case for very coarse material), or they can incorporate mechanisms to shake or vibrate the screen.
Concentration
In chemistry, concentration is defined as the number of moles of a solute in a volume of the solution. In case of mineral processing, concentration means the increase of the percentage of the valuable mineral in the concentrate (mixture of gangue and valuable mineral). There are a number of ways to increase the concentration of the wanted minerals, which include:
Gravity concentration
Gravity separation is the separation of two or more minerals of different specific gravity by their relative movement in response to the force of gravity and one or more other forces (such as centrifugal forces, magnetic forces, buoyant forces), one of which is resistance to motion (drag force) by a viscous medium such as heavy media, water or, less commonly, air.
Gravity separation is one of the oldest techniques in mineral processing but has seen a decline in its use since the introduction of methods like flotation, classification, magnetic separation and leaching.
Froth flotation
Froth flotation is an important concentration process. The froth flotation is used with sulphide ores (e.g. CuS or ZnS). The ore is powdered, fed into water tanks and made into slurry with water. Then “frothing” chemicals (suitable oils) are added. Sulphides are attracted to these chemicals. When air is blown through the slurry, froth rises to the top of the tank carrying the metal sulphides with it. Then they are skimmed off and dried. The gangue sinks.
Electrostatic separation
This kind of concentration process involves passing a stream of particles past a charged anode plate. The particles that are conductors lose electrons to the plate and are pulled away from the other particles due to the induced attraction to the anode and are removed from the mixture. For efficient separation to occur the particles must be extremely small (between 75 and 250 micron), the particles need to be dry, have a close size distribution and uniform in shape. Of these considerations, one of the most important is the water content of the particles. This is important as a layer of moisture on the particles will render the non-conductors as conductors as the layer of the water is conductive.
Magnetic separation
Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force. This separation technique can be useful in mining iron as it is attracted to a magnet. This process of separating magnetic substances from the non-magnetic substances in a mixture with the help of a magnet is called magnetic separation.
Automated ore sorting
Modern, automated sorting applies optical sensors (visible spectrum, near infrared, X-ray, ultraviolet), that can be coupled with electrical conductivity and magnetic susceptibility sensors, to control the mechanical separation of ore into two or more categories on an individual rock by rock basis. Also new sensors have been developed which exploit material properties such as electrical conductivity, magnetization, molecular structure and thermal conductivity. Sensor based sorting has found application in the processing of nickel, gold, copper, coal and diamonds.
Dewatering
Dewatering is an important process in mineral processing. The purpose of dewatering is to remove water absorbed by the particles. This is done for a number of reasons, specifically, to enable ore handling and concentrates to be transported easily, allow further processing to occur and to dispose of the gangue. The water extracted from the ore by dewatering is reused for plant operations after being sent to a water treatment plant.
After learning about general processes of mineral extraction, let us now turn to specific processing of individual minerals. The following are the descriptions of the ways in which various, named minerals are processed:
Iron processing
The process of iron extraction is carried out by the following steps:
- Concentration of ore:In this metallurgical operation, the ore is concentrated by removing impurities like soil etc. The process involves the crushing and washing of ore.
- Calcination or roasting of ore:The concentrated ore is now heated in the presence of air. The process of roasting is performed to convert the iron to iron (III) oxide, Fe2O3. Before being introduced into the blast furnace, all forms of iron ore must be converted into the oxide.
- Reduction of ore:The process of reduction is carried out in a blast furnace. The blast furnace is a cylindrical tower in which the ore is reduced to iron metal. Iron ore, coke and limestone are mixed together to give a mixture called charge. The charge is introduced into the blast furnace.
In the blast furnace, carbon is oxidized to carbon monoxide gas. The carbon monoxide gas reduces the iron (III) oxide to molten iron, which is removed as either pig iron or cast iron. This is the raw material for production of iron, steel and other products. Pig iron is made into steel by melting it to remove all its impurities, after which small amounts of other metals are added to make different types of steel.
The impurities in the ore, mainly silicon oxide (silica) reacts with limestone to form calcium silicate (slag) which is tapped off from the furnace and put into various uses.
Iron processing
Copper processing
Copper ore is mined in open pits and below ground. The mined ore is ground, concentrated and slurried with water and chemical reagents. Air is blown through the mixture and attaches to the copper, causing it to float to the top of the slurry. The copper is then removed with skimmer (a machine that separates a liquid from particles floating on it or from another liquid). The tailings (materials left over after the mineral has been separated from the gangue of an ore) remain and are dewatered and disposed off in tailing ponds. The water is recovered and recycled.
The concentrated copper recovered through floatation is dried and then smelted in copper smelters. The smelters reduce the concentrate to copper blisters. The copper blisters contain 97–98% of pure copper. To get pure copper, which must have a purity of 99% to be effective for electrical wiring and other purposes, the copper blisters are purified by electrolysis. This purification process is called copper refining.
Gold processing
The ore is crushed and dissolved in a solution of sodium cyanide. The chemical dissolves the gold particles leaving behind stone and other mineral waste. The sodium cyanide solution containing gold particles is drained off and mixed with zinc dust which causes the gold particles to solidify. The particles are then separated, dried, melted and moulded into bars called ingots.
Aluminium processing
Aluminium is processed by the following three steps:
- Concentration of the ore:Aluminium ore, bauxite, is mined from the ground by open-cast mining. The ore is then sorted, crushed, grinded and fed into large grinding mills where it is mixed with sodium hydroxide solution at high temperatures and pressure. The grinding mill grinds the ore to an even finer size. The material finally discharged from the mill is called slurry.The resulting liquor contains a solution of sodium aluminate and undissolved bauxite residues containing iron, silicon and titanium. These residues, commonly referred to as “red mud”, gradually sink to the bottom of the tank and are removed.
- Purification of the ore:The sodium aluminate obtained in the above stage is purified through a number of industrial processes to get aluminium oxide (alumina).
- Electrolysis:The purified aluminium oxide is then electrolysed to get pure aluminium metal. Because aluminium oxide has a high melting point, it dissolved in molten cryolite to lower its melting point because it is too expensive to carry out electrolysis at very high temperatures.During electrolysis the molten metal falls to the bottom of the electrolytic cell and is tapped off.
Oil Production in the Middle East
Oil production in the Middle East
The Middle East is the largest oil-producing region in the world. It accounts for over one third of the total world production. Te major producers of oil in this region include Saudi Arabia, Iraq, Kuwait, Iran and the United Arab Emirates. Others include Bahrain, Qatar and Yemen.
Most of these countries are members of the Organization of Petroleum Producing countries (OPEC), an intergovernmental organization which plays key role in managing and overseeing the oil industry, including fixing of the oil price and regulation of oil production among member states, among other functions.
The prospection, drilling, refining and transportation of petroleum are mainly carried out by international companies from Europe and America.
A portion of the oil is refined in oil refineries within the Middle East while the rest is exported overseas as crude oil.
Natural Gas Production in Tanzania
Natural gas production in Tanzania
Natural gas is a fossil fuel formed when layers of buried organic matter are exposed to intense heat and pressure over thousands of years. It is used for various purposes such as generation of electricity, fuelling machines, cooking, heating, etc.
Tanzania has recently managed to exploit this mineral at Songosongo in Kilwa, Lindi region. The gas is processed at Songosongo and then transported via pipeline to Dar es Salaam where plans are under way to use the resource to generate electricity. It will also be supplied to homes and industries for heating and other operations.
The country has so far four natural gas fields, namely Songosongo, Mnazi Bay, Mkuranga and Kiliwani North. Of these, only two gas fields – Songosongo and Mnazi Bay – are producing. The rest are still being developed.
Advantages of Oil Production in the Middle East and Natural Gas Production in Tanzania
Describe advantages of oil production in the Middle East and natural gas production in Tanzania
Advantages of oil production in the Middle East
- Source of foreign currency:Most of the oil used in many parts of the world comes from the Middle East. A large amount of oil is exported from this region, so the countries earn the much needed foreign exchange which is, in turn, invested in others sectors such as manufacturing industries, commerce and trade.
- Creation of employment opportunities:Most of the Middle East countries lie entirely in the heart of the desert. So it is hard to undertake other economic activities such as agriculture. Most people are solely employed in the oil production industry, which provides them with income that they spend on their basic needs. People are employed to work in oil extraction, transportation, or sale of petroleum products.
- Improvement of social services:The money earned from the oil industry is invested in other sectors of economy. It is also used to established or improve social services and other amenities. The governments spend huge sums of money to set up social services such as schools, hospitals, games and sports, etc.
- Improvement of transport and communication:The income generated by the oil industry is used to develop roads railways, harbours, and airports. This has consequently led to improvement of transportation and communication infrastructures in the region.
- Generation of energy and power:The oil produced provides the Middle East countries with energy and power that is used for various purposes, including running vehicles and other machinery.
Advantages of natural gas production in Tanzania
- The industry is a source of employment opportunities to Tanzanians since many people are directly employed in the gas sector as prospectors, engineers, miners, transporters, etc. This helps to curb the problem of unemployment as well as improving the living standards of the people.
- Discovery of natural gas in remote areas of Lindi, Coast and other parts has helped to solve the problem of rural–urban migration since people now can stay in the rural areas and engage in gas production. This has greatly helped reduce the population pressure in urban areas as well as minimize the problems associated with overpopulation.
- One of the major uses of natural gas is the production of cost-effective electricity. It is expected that when more electricity generated from natural gas will be available to consumers, the cost of electricity will drop significantly. This will, in turn, reduce the burden of high living costs to Tanzanians.
- Cheap electricity generated from natural gas will soon be supplied to industries. The cost of production of goods and services will thus be cut short. Hence, the goods and services will be available to people cheaply. This will lower the cost of living and hence improve the living standards of the people.
- Exportation of natural gas and sale of electricity will increase the government revenue. The revenue collected will then be used to improve public services to people around the gas fields and the entire country in general.
- Due to availability of cheap electricity people will no longer cut down trees for firewood and charcoal. This will help conserve the forest and the environment.
Disadvantage of natural gas production in Tanzania
- Even though people are compensated when they give their lands for construction and expansion of gas projects, the compensation is very small. The houses and other infrastructure belonging to poor people are demolished carelessly before they are compensated or relocated, a fact that bothers these citizens a great deal.
- The natural gas is a highly explosive substance. It can cause great loss of life and property to the people living or undertaking their activities close to gas pipelines in case the gas in the pipeline explodes and catches fire spontaneously.
- Because the gas is a non-renewable resource, it can be exhausted or get used up. This could destabilize the activities and sectors whose existence relies upon the availability of natural gas.
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