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If we were to cut the Earth in half we would see that our planet is made up of a number of layers, namely the core at the centre (seperated into the inner and outer core), the mantle, the upper mantle, the outer crust and the atmosphere (Figure 1). The core is made up mostly of iron. The mantle, which lies between the core and the crust, consists of molten rock, called magma which moves continuously because of convection currents. The crust is the thin, hard outer layer that 'floats' on the magma of the mantle. It is the upper part of the mantle and the crust that make up the lithosphere ('lith' means 'types of stone' and 'sphere' refers to the round shape of the earth). Together, the lithosphere, hydrosphere and atmosphere make up the world as we know it.
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The lithosphere is the solid outermost shell of our planet. The lithosphere includes the crust and the upper part of the mantle, and is made up of material from both the continents and the oceans on the Earth's surface.
In grade 10 have focused on the hydrosphere and the atmosphere. The lithosphere is also very important, not only because it is the surface on which we live, but also because humans gain many valuable resources from this part of the planet.
The crust is made up of about 80 elements, which occur in over 2000 different compounds and minerals. However, most of the mass of the material in the crust is made up of only 8 of these elements. These are oxygen (O), silica (Si), aluminium (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K) and magnesium (Mg). These metal elements are seldom found in their pure form, but are usually part of other more complex minerals. A mineral is a compound that is formed through geological processes, which give it a particular structure. A mineral could be a pure element, but more often minerals are made up of many different elements combined. Quartz is just one example. It is a mineral that is made up of silicon and oxygen. Some more examples are shown in Table 1.
Minerals are natural compounds formed through geological processes. The term 'mineral' includes both the material's chemical composition and its structure. Minerals range in composition from pure elements to complex compounds.
| Mineral | Chemistry | Comments |
| Quartz | SiO |
Quartz is used for glass, in electrical components, optical lenses and in building stone |
| Gold | Au (pure element) or AuTe |
Gold is often found in a group of minerals called the tellurides. Calaverite is a mineral that belongs to this group, and is the most common gold-bearing mineral. Gold has an affinity for tellurium (Te). |
| Hematite | Fe |
Iron usually occurs in iron oxide minerals or as an alloy of iron and nickel. |
| Orthoclase | KAlSi |
Orthoclase belongs to the feldspar group of minerals. |
| Copper | Cu (pure element) or Cu |
copper can be mined as a pure element or as a mineral such as malachite. |
A rock is a combination of one or more minerals. Granite for example, is a rock that is made up of minerals such as SiO
Many of the elements that are of interest to us (e.g. gold, iron, copper), are unevenly distributed in the lithosphere. In places where these elements are abundant, it is profitable to extract them (e.g. through mining) for economic purposes. If their concentration is very low, then the cost of extraction becomes more than the money that would be made if they were sold. Rocks that contain valuable minerals are called ores. As humans, we are particularly interested in the ores that contain metal elements, and also in those minerals that can be used to produce energy.
An ore is a volume of rock that contains minerals which make it valuable for mining.
Many of the minerals that are important to humans are metals such as gold, aluminium, copper and iron. Throughout history, metals have played a very important role in making jewelery, tools, weapons and later machinery and other forms of technology. We have become so used to having metals around us that we seldom stop to think what life might have been like before metals were discovered. During the Stone Age for example, stones were used to make tools. Slivers of stone were cut from a rock and then sharpened. In Africa, some of the stone tools that have been found date back to 2.5 million years ago!
It was the discovery of metals that led to some huge advances in agriculture, warfare, transport and even cookery. One of the first metals to be discovered was gold, probably because of its beautiful shiny appearance. Gold was used mostly to make jewelery because it was too soft to make harder tools. Later, copper became an important metal because it could be hammered into shape, and it also lasted a lot longer than the stone that had previously been used in knives, cooking utensils and weapons. Copper can also be melted and then put into a mould to re-shape it. This is known as casting.
At about the time that copper was in widespread use, it was discovered that if certain kinds of stones are heated to high enough temperatures, liquid metals flow from them. These rocks are ores, and contain the metal minerals inside them. The process of heating mineral ores in this way is called smelting. It was also found that ores do not only occur at the earth's surface, but also deep below it. This discovery led to the beginning of mining.
But humans' explorations into the world of metals did not end here! In some areas, the ores of iron and tin were found close together. The cast alloy of these two metals is bronze. Bronze is a very useful metal because it produces a sharper edge than copper. Another important discovery was that of iron. Iron is the most abundant metal at the earth's surface but it is more difficult to work with than copper or tin. It is very difficult to extract iron from its ore because it has an extremely high melting point, and only specially designed furnaces are able to produce the temperatures that are needed. An important discovery was that if iron is heated in a furnace with charcoal, some of the carbon in the charcoal is transferred to the iron, making the metal even harder. If this hot metal has its temperature reduced very suddenly, it becomes even harder and produces steel. Today, steel is a very important part of industry and construction.
Apart from minerals and ores, the products of the lithosphere are also important in meeting our energy needs.
Coal is one of the most important fuels that is used in the production of electricity. Coal is formed from organic material when plants and animals decompose, leaving behind organic remains that accumulate and become compacted over millions of years under sedimentary rock. The layers of compact organic material that can be found between sedimentary layers, are coal. When coal is burned, a large amount of heat energy is released, which is used to produce electricity. South Africa is the world's sixth largest coal producer, with Mpumalanga contributing about 83% of our total production. Other areas in which coal is produced, include the Free State, Limpopo and KwaZulu-Natal. One of the problems with coal however, is that it is a non-renewable resource, meaning that once all resources have been used up, it cannot simply be produced again. Burning coal also produces large quantities of greenhouse gases, which may play a role in global warming. At present, ESKOM, the South African government's electric power producer, is the coal industry's main customer.
Another element that is found in the crust, and which helps to meet our energy needs, is uranium. Uranium produces energy through the process of nuclear fission. Neutrons are aimed at the nucleii of the uranium atoms in order to split them. When the nucleus of a uranium atom is split, a large amount of energy is released as heat. This heat is used to produce steam, which turns turbines to generate electricity. Uranium is produced as a by-product of gold in some mines in the Witwatersrand, and as a by-product in some copper mines, for example in Phalaborwa. This type of nuclear power is relatively environmentally friendly since it produces low gas emissions. However, the process does produce small amounts of radioactive wastes , which must be carefully disposed of in order to prevent contamination.
Oil is another product of the lithosphere which is critical in meeting our fuel needs. While most of South Africa's oil is imported and then processed at a refinery in either Durban, Cape Town or Sasolburg, some is extracted from coal. The technology behind this type of extraction has largely been developed by SASOL (South African Coal, Oil and Gas Corporation). Oil, like coal, is organic in origin and normally forms from organic deposits on the ocean floor. Oil requires unique geological and geochemical conditions in order to be produced. Part of this process involves the burial of organic-rich sediments under extremely high temperatures and pressures. The oil that is produced is then pushed out into nearby sedimentary layers. Oil will then move upwards until it is trapped by an impermeable rock layer. It accumulates here, and can then be accessed by oil rigs and other advanced equipment.
Using any reference resources you have available, try to find a map of the mining regions of South Africa.
Gold was discovered in South Africa in the late 1800's and since then has played a very important role in South Africa's history and economy. Its discovery brought many foreigners into South Africa, who were lured by the promises of wealth. They set up small mining villages, which later grew into larger settlements, towns and cities. One of the first of these settlements was the beginning of present-day Johannesburg, also known as 'Egoli' or 'Place of Gold'.
Most of South Africa's gold is concentrated in the 'Golden Arc', which stretches from Johannesburg to Welkom. Geologists believe that, millions of years ago, this area was a massive inland lake. Rivers feeding into this lake brought sand, silt, pebbles and fine particles of gold and deposited them over a long period of time. Eventually these deposits accumulated and became compacted to form gold-bearing sedimentary rock or gold reefs. It is because of this complex, but unique, set of circumstances that South Africa's gold deposits are so concentrated in that area. In other countries like Zimbabwe, gold occurs in smaller 'pockets', which are scattered over a much greater area.
A number of different techniques can be used to mine gold. The three most common methods in South Africa are panning, open cast and shaft mining.
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For every ton of ore that is mined, only a very small amount of gold is extracted. A number of different methods can be used to separate gold from its ore, but one of the more common methods is called gold cyanidation.
In the process of gold cyanidation, the ore is crushed and then cyanide (CN
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Gold has a number of uses because of its varied and unique characteristics. Below is a list of some of these characteristics that have made gold such a valuable metal:
Read the article below, which has been adapted from one that appeared in the Financial Mail on 15th April 2005 and then answer the questions that follow.
As recently as 1980, South Africa accounted for over 70% of world gold production. In 2004, that figure was a dismal 14%. Chamber of Mines figures showed that SA's annual gold production last year slipped to its lowest level since 1931.
Chamber economist Roger Baxter says the 'precipitous' fall in production was caused by the dual impact of the fall in the rand gold price due to the strong rand, and the continued upward rise in costs. Many of these costs, laments Baxter, are 'costs we do not have control over'. These include water, transport, steel and labour costs, which rose by 13% on average in 2004.
He provides a breakdown of the cost components faced by mines:
At these costs, and at current rand gold prices, about 10 mines, employing 90 000 people, are marginal or loss-making, says Baxter.
| Year | Production (t) |
| 1980 | 675 |
| 1985 | 660 |
| 1990 | 600 |
| 1995 | 525 |
| 2000 | 425 |
| 2004 | 340 |
However, despite the incredible value of gold and its usefulness in a variety of applications, all mining has an environmental cost. The following are just a few of the environmental impacts of gold mining:
There is a growing emphasis on the need to rehabilitate old mine sites that are no longer in use. If it is too difficult to restore the site to what it was before, then a new type of land use might be decided for that area. Any mine rehabilitation programme should aim to achieve the following:
There are different ways to achieve these goals. Plants for example, can be used to remove metals from polluted soils and water, and can also help to stabilise the soil so that other vegetation can grow. Land contouring can help to restore drainage in the area.
Discussion:
In groups of 3-4, discuss the following questions:
Mapungubwe in the Limpopo Province is evidence of gold mining in South Africa as early as 1200. Today, South Africa is a world leader in the technology of gold mining. The following flow diagram illustrates some of the most important steps in the recovery of gold from its ore.
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Iron is one of the most abundant metals on Earth. Its concentration is highest in the core, and lower in the crust. It is extracted from iron ore and is almost never found in its elemental form. Iron ores are usually rich in iron oxide minerals and may vary in colour from dark grey to rusty red. Iron is usually found in minerals such as magnetite (Fe
One of the more common methods of mining for iron ore is open cast mining. Open cast mining is used when the iron ore is found near the surface. Once the ore has been removed, it needs to be crushed into fine particles before it can be processed further.
As mentioned earlier, iron is commonly found in the form of iron oxides. To create pure iron, the ore must be smelted to remove the oxygen.
Smelting is a method used to extract a metal from its ore and then purify it.
Smelting usually involves heating the ore and also adding a reducing agent (e.g. carbon) so that the metal can be freed from its ore. The bonds between iron and oxygen are very strong, and therefore it is important to use an element that will form stronger bonds with oxygen that the iron. This is why carbon is used. In fact, carbon monoxide is the main ingredient that is needed to strip oxygen from iron. These reactions take place in a blast furnace.
A blast furnace is a huge steel container many metres high and lined with heat-resistant material. In the furnace the solid raw materials, i.e. iron ore, carbon (in the form of 'coke', a type of coal) and a flux (e.g. limestone) are fed into the top of the furnace and a blast of heated air is forced into the furnace from the bottom. Temperatures in a blast furnace can reach 2000
STEP 1: Production of carbon monoxide
STEP 2: Reduction of iron oxides takes place in a number of stages to produce iron.
STEP 3: Fluxing
The flux is used to melt impurities in the ore. A common flux is limestone (CaCO
In step 3, the calcium carbonate breaks down into calcium oxide and carbon dioxide. The calcium oxide then reacts with silicon dioxide (the impurity) to form a slag. In this case the slag is the CaSiO
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Iron is the most used of all the metals. Its combination of low cost and high strength make it very important in applications such as industry, automobiles, the hulls of large ships and in the structural components of buildings. Some of the different forms that iron can take include:
One problem with iron and steel is that pure iron and most of its alloys rust. These products therefore need to be protected from water and oxygen, and this is done through painting, galvanisation and plastic coating.
The primary steel industry is an important part of the South African economy and it generates a great deal of foreign exchange.
Iron is usually extracted from heamatite (iron(III)oxide). Iron ore is mixed with limestone and coke in a blast furnace to produce the metal. The following incomplete word equations describe the extraction process:
(DoE Exemplar Paper, Grade 11, 2007)
A phosphate is a salt of phosphoric acid (H
Phosphate is found in beds in sedimentary rock, and has to be quarried to access the ore. A quarry is a type of open pit mine that is used to extract ore. In South Africa, the main phosphate producer is at the Palaborwa alkaline igneous complex, which produces about 3 million tons of ore per year. The ore is crushed into a powder and is then treated with sulfuric acid to form a superphosphate (Ca(H
Alternatively, the ore can be treated with concentrated phosphoric acid (which forms a triple superphosphate), in which case the reaction looks like this:
Phosphates are mostly used in agriculture. Phosphates are one of the three main nutrients needed by plants, and they are therefore an important component of fertilisers to stimulate plant growth.
Rock phosphate [Ca
(DoE Exemplar Paper, Grade 11, 2007)
Read the extract below, which has been adapted from an article that appeared in the Mail and Guardian on 4th May 2007, and then answer the questions that follow.
A potentially violent backlash looms in Pondoland over efforts by an Australian company to persuade villagers to back controversial plans to mine an environmentally sensitive strip of the Wild Coast. The mining will take place in the Xolobeni dunes, south of Port Edward. The application has outraged environmental groups, largely because the proposed mining areas form part of the Pondoland centre of endemism, which has more species than the United Kingdom, some of which are endemic and facing extinction.
Exploratory drilling revealed Xolobeni has the world's 10th largest titanium deposit, worth about R11 billion. The amount of money that will be spent over the mine's 22 years, including a smelter, is estimated at R1.4 billion. The Australian mining company predicts that 570 direct jobs will be created.
But at least two communities fiercely oppose the mining plans. Some opponents are former miners who fear Gauteng's mine dumps and compounds will be replicated on the Wild Coast. Others are employees of failed ecotourism ventures, who blame the mining company for their situation. Many are suspicious of outsiders. The villagers have also complained that some of the structures within the mining company are controlled by business leaders with political connections, who are in it for their own gain. Intimidation of people who oppose the mining has also been alleged. Headman Mandoda Ndovela was shot dead after his outspoken criticism of the mining.
Mzamo Dlamini, a youth living in one of the villages that will be affected by the mining, said 10% of the Amadiba 'who were promised riches by the mining company' support mining. 'The rest say if people bring those machines, we will fight.'
The products of the lithosphere are also important in meeting our energy needs. Coal is one product that is used to produce energy. In South Africa, coal is particularly important because most of our electricity is generated using coal as a fuel. South Africa is the world's sixth largest coal producer, with Mpumalanga contributing about 83% of our total production. Other areas in which coal is produced, include the Free State, Limpopo and KwaZulu-Natal. One of the problems with coal however, is that it is a non-renewable resource, meaning that once all resources have been used up, it cannot simply be produced again. Burning coal also produces large quantities of greenhouse gases, which may play a role in global warming. At present, ESKOM, the South African government's electric power producer, is the coal industry's main customer.
Coal is what is known as a fossil fuel. A fossil fuel is a hydrocarbon that has been formed from organic material such as the remains of plants and animals. When plants and animals decompose, they leave behind organic remains that accumulate and become compacted over millions of years under sedimentary rock. Over time, the heat and pressure in these parts of the earth's crust also increases, and coal is formed. When coal is burned, a large amount of heat energy is released, which is used to produce electricity. Oil is also a fossil fuel and is formed in a similar way.
A fossil fuel is a hydrocarbon that is formed from the fossilised remains of dead plants and animals that have been under conditions of intense heat and pressure for millions of years.
Coal can be removed from the crust in a number of different ways. The most common methods used are strip mining, open cast mining and underground mining.
Although in South Africa, the main use of coal is to produce electricity, it can also be used for other purposes.
In South Africa, the coal industry is second only to the gold industry. More than this, South Africa is one of the world's top coal exporters, and also one of the top producers. Of the coal that is produced, most is used locally to produce electricity and the rest is used in industry and domestically.
The problem with coal however, is that it is a non-renewable resource which means that once all the coal deposits have been mined, there will be none left. Coal takes such a long time to form, and requires such specific environmental conditions, that it would be impossible for coal to re-form at a rate that would keep up with humankind's current consumption. It is therefore very important that South Africa, and other countries that rely on coal, start to look for alternative energy resources.
There are a number of environmental impacts associated with coal mining.
The following advertisement appeared in a local paper:
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(DoE Exemplar Paper 2, Grade 11, 2007)
Oil is another product of the lithosphere which is very important in meeting our fuel needs.
Oil is formed in a very similar way to coal, except that the organic material is laid down in oceans. Organisms such as zooplankton and algae settle to the ocean floor and become buried under layers of mud. Over time, as these layers of sediment accumulate and the heat and pressure also increase, the organic material changes to a waxy material called kerogen. Eventually, with continuing heat and pressure, liquid and gas hydrocarbons are formed. These hydrocarbons are lighter than rock and therefore move upwards through the rock layers before being trapped by an impermeable layer. Here the oil will slowly accumulate until there is enough that it can be accessed by oil rigs and other equipment. Crude oil or petroleum, is actually a mixture of hydrocarbons (mostly alkanes) of different lengths, ranging from 5 carbons to 18 carbons in the hydrocarbon chain. If the mixture contains mostly short hydrocarbons, then it is a gas called natural gas. As the hydrocarbon chains in the mixture become longer, the product becomes more and more solid. Coal is made up of the longest hydrocarbons. For more information on hydrocarbons, refer to Grade 12.
When enough oil has accumulated in a well, it becomes economically viable to try to extract it either through drilling or pumping. If the pressure in the oil reservoir is high, the oil is forced naturally to the surface. This is known as primary recovery of oil. If the pressure is low, then pumps must be used to extract it. This is known as secondary recovery. When the oil is very difficult to extract, steam injection into the reservoir can be used to heat the oil, reduce its viscosity and make it easier to extract.
While most of South Africa's oil is imported and then processed at a refinery in either Durban, Cape Town or Sasolburg, some is extracted from coal, as discussed in "Energy resources and their uses".
Oil can also be used to make a variety of different products. You will find more information on this in Grade 12.
Some of the key environmental impacts associated with the extraction and use of oil are as follows:
As the world's population increases, so does the demand for energy. As we have already mentioned, many of our energy resources are non-renewable and will soon run out. In addition, many of the fuels that we use produce large amounts of greenhouse gases, which can contribute towards global warming. If we are to maintain the quality and health of our planet, and also meet our growing need for energy, we will need to investigate alternative energy resources. In this next section, we are going to take a closer look at some of these possible alternatives. Many of these options are very controversial, and may have both pros and cons.
The massive power cuts or 'load shedding' that South Africans began to experience at the beginning of 2008, were a dramatic wake-up call to the growing energy crisis that the country faces.
There are alternative energy sources available, but they will take years to become functional, and many of them have their own problems. Another way to look at the problem, is to put the focus on reducing how much energy is used rather than focusing only on ways to meet the growing demand.
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This work is licensed by Rory Adams, Free High School Science Texts Project, Mark Horner, and Heather Williams under a Creative Commons Attribution License (CC-BY 3.0), and is an Open Educational Resource.
Last edited by Free High School Science Texts Project on Nov 3, 2010 4:53 am -0500.
