description of processes and machinery required to extract gold from the lithosphere for golf in terms of opencast mining or und

mponeng gold mine, gauteng - mining technology | mining news and views updated daily

mponeng gold mine, gauteng - mining technology | mining news and views updated daily

AngloGold Ashantis Mponeng mine is located in Gauteng province of South Africa. It is mined to an average depth of 2,800m-3,400m below surface and is one of the worlds deepest and richest gold mines with grades at over 8g/t. It is one of three AngloGold projects in the West Witts area apart from Savuka and TauTona mines. The name means look at me in the local Sotho language.

Formerly the Western Deep Levels South Shaft, or Shaft No 1, Mponeng is the most recently sunk of the three former Western Deep Levels mines. Sinking of Mponeng shafts began in 1981, and the main shaft was completed in 1986, with the subshaft completed in 1993.

Currently all production is sourced from the VCR (Ventersdorp Contact Reef). The mine has been expanded through many deepening projects with the latest one being the extension from 109 to 120 levels. Work is currently in progress to extract the ore from the Carbon Leader Reef (CLR) below it.

The project will facilitate the development of many other smaller projects and extend the mine life. It is yet to be approved by the company board. The other major project, VCR below 120, entails accessing the mineral reserves below 120 level. AngloGold Ashanti estimates that this project will add 2.5Moz to production for 10 years at a cost of R2.03bn ($252m).

The VCR below 120 project is expected to increase the mines life by eight years to 2024. The project was approved by the board in February 2007, following which construction began. On-reef development and thus the start of production is scheduled for 2013 with full production due in 2015.

Mponeng is located on the north-western rim of the Witwatersrand Basin. There are seven gold bearing conglomerates within the lease area, of which two are economically viable at present. The VCR is a gold-bearing quartz-pebble conglomerate of intermediate grade, capping the last angular Witwatersrand non-conformity.

The South shaft deepening project commenced in 1996 and as a result Mponeng mines the Ventersdorp Contact Reef (VCR) to the 120 level, which is some 3.4km below datum. Mponeng mines on average at deeper than 2.7km below the surface. The VCR reef that Mponeng mines dips at 22, and has an average channel width of 78cm.

The deepest operating stope is at a depth of 3.37km below surface. The grade at this operation varies considerably, therefore a sequential grid mining method is used which allows for selective mining and increased flexibility in dealing with changes in grade ahead of the stope. The mine utilises a twin-shaft system housing two vertical shafts and two service shafts.

Exploration drilling for the CLR below 120 project commenced in early 2008. CLR comprises three economical units. Unit 3 is centrally located and is the oldest of the CLR deposits. Unit 2 is a small size complex channel deposit situated in the east of Unit 3. The unavailability of infrastructure to access these units raised the opportunity of containing additional ounces of gold at the mine.

Ore mined is treated and smelted at Mponengs gold plant. The ore is initially ground down by means of semiautogenous milling after which a conventional gold leach process incorporating liquid oxygen injection is applied. The gold is then extracted by means of carbon-in-pulp (CIP) technology. The plant conducts electro-winning and smelting (induction furnaces) on products from Savuka and TauTonaas well.

The various planned and unplanned work stoppages and safety initiatives conducted towards the end of the year, combined with a decline in grade and reduced face advance, contributed to the decrease in production.

There was a 4% decline in the area mined in 2007, largely as a result of a 3% decrease in face length. Mponeng undertook extensive cost cutting measures throughout the year. Gold Production at the Mponeng mine in 2010 was 532,000oz.

iron and steel - introduction to their science, properties, uses

iron and steel - introduction to their science, properties, uses

Think of the greatest structures of the 19th centurythe Eiffel Tower, the Capitol, the Statue of Libertyand you'll be thinking of iron. [1] The fourth most common element in Earth's crust, iron has been in widespread use now for about 6000 years. Hugely versatile, and one of the strongest and cheapest metals, it became an important building block of the Industrial Revolution, but it's also an essential element in plant and animal life. Combined with varying (but tiny) amounts of carbon, iron makes a much stronger material called steel, used in a huge range of human-made objects, from cutlery to warships, skyscrapers, and space rockets. Let's take a closer look at these two superb materials and find out what makes them so popular!

Photo: The world's first cast-iron bridge, after which the village of Ironbridge in Shropshire, England was named. It was built across the River Severn by Abraham Darby III in 1779 using some 384 tons of iron. You can read more about its history and construction on the official Ironbridge website. Photo by Jason Smith courtesy of Wikimedia Commons.

Photo: A sample of iron from a meteorite (next to a pen for scale). From the mineral collection of Brigham Young University Department of Geology, Provo, Utah. Photograph by Andrew Silver courtesy of US Geological Survey Photographic Library.

You might think of iron as a hard, strong metal tough enough to support bridges and buildings, but that's not pure iron. What we have there is alloys of iron (iron combined with carbon and other elements), which we'll explain in more detail in a moment. Pure iron is a different matter altogether. Consider its physical properties (how it behaves by itself) and its chemical properties (how it combines and reacts with other elements and compounds).

Pure iron is a silvery-white metal that's easy to work and shape and it's just soft enough to cut through (with quite a bit of difficulty) using a knife. You can hammer iron into sheets and draw it into wires. Like most metals, iron conducts electricity and heat very well and it's very easy to magnetize.

The reason we so rarely see pure iron is that it combines readily with oxygen (from the air). Indeed, iron's major drawback as a construction material is that it reacts with moist air (in a process called corrosion) to form the flaky, reddish-brown oxide we call rust. Iron reacts in lots of other ways toowith elements ranging from carbon, sulfur, and silicon to halogens such as chlorine.

Broadly, iron's compounds can be divided into two groups known as ferrous and ferric (the old names) or iron (II) and iron (III); you can always substitute "iron(II)" for "ferrous" and "iron(III)" for "ferric" in compound names.

Iron is the fourth most common element in Earth's crust (after oxygen, silicon, and aluminum), and the second most common metal (after aluminum), but because it reacts so readily with oxygen it's never mined in its pure form (though meteorites are occasionally discovered that contain samples of pure iron). Like aluminum, most iron "locked" inside Earth exists in the form of oxides (compounds of iron and oxygen). Iron oxides exist in seven main ores (raw, rocky minerals mined from Earth):

Different ores contain different amounts of iron. Hematite and magnetite have about 70 percent iron, limonite has about 60 percent, pyrite and siderite have 50 percent, while taconite has only 30 percent. Using a combination of both deep mining (under the ground) and opencast mining (on the surface), the world produces approximately 1000 million tons of iron ore each year, with China responsible for just over half of it.

Which countries produce the world's iron? As you can see, China utterly dominates as the source of almost two thirds of the iron we use. Chart shows estimated figures for pig iron for 2019. In the United States, three companies currently produce pig iron in nine different locations. Source: US Geological Survey, Mineral Commodity Summaries, January 2020.

Pure iron is too soft and reactive to be of much real use, so most of the "iron" we tend to use for everyday purposes is actually in the form of iron alloys: iron mixed with other elements (especially carbon) to make stronger, more resilient forms of the metal including steel. Broadly speaking, steel is an alloy of iron that contains up to about 2 percent carbon, while other forms of iron contain about 24 percent carbon. In fact, there are thousands of different kinds of iron and steel, all containing slightly different amounts of other alloying elements.

Basic raw iron is called pig iron because it's produced in the form of chunky molded blocks known as pigs. Pig iron is made by heating an iron ore (rich in iron oxide) in a blast furnace: an enormous industrial fireplace, shaped like a cylinder, into which huge drafts of hot air are introduced in regular "blasts". Blast furnaces are often spectacularly huge: some are 3060m (100200ft) high, hold dozens of trucks worth of raw materials, and often operate continuously for years at a time without being switched off or cooled down. Inside the furnace, the iron ore reacts chemically with coke (a carbon-rich form of coal) and limestone. The coke "steals" the oxygen from the iron oxide (in a chemical process called reduction), leaving behind a relatively pure liquid iron, while the limestone helps to remove the other parts of the rocky ore (including clay, sand, and small stones), which form a waste slurry known as slag. The iron made in a blast furnace is an alloy containing about 9095 percent iron, 34 percent carbon, and traces of other elements such as silicon, manganese, and phosphorus, depending on the ore used. Pig iron is much harder than 100 percent pure iron, but still too weak for most everyday purposes.

Photo: The cast-iron dome of the US Capitol. Credit: The George F. Landegger Collection of District of Columbia Photographs in Carol M. Highsmith's America, Library of Congress, Prints and Photographs Division.

One of the world's most famous iron buildings, the Capitol in Washington, DC has a dome made of 4,041,146kg (8,909,200 pounds) of cast iron. Cast iron is simply liquid iron that has been cast: poured into a mold and allowed to cool and harden to form a finished structural shape, such as a pipe, a gear, or a big girder for an iron bridge. Pig iron is actually a very basic form of cast iron, but it's molded only very crudely because it's typically melted down to make steel. The high carbon content of cast iron (the same as pig ironroughly 34 percent) makes it extremely hard and brittle: large crystals of carbon embedded in cast iron stop the crystals of iron from moving about. Cast iron has two big drawbacks: first, because it's hard and brittle, it's virtually impossible to shape, even when heated; second, it rusts relatively easily. It's worth noting that there are actually several different types of cast iron, including white and gray cast irons (named for the coloring of the finished product caused by the way the carbon inside it behaves).

Cast iron assumes its finished shape the moment the liquid iron alloy cools down in the mold. Wrought iron is a very different material made by mixing liquid iron with some slag (leftover waste). The result is an iron alloy with a much lower carbon content. Wrought iron is softer than cast iron and much less tough, so you can heat it up to shape it relatively easily, and it's also much less prone to rusting. However, relatively little wrought iron is now produced commercially, since most of the objects originally produced from it are now made from steel, which is both cheaper and generally of more consistent quality. Wrought iron is what people used to use before they really mastered making steel in large quantities in the mid-19th century.

Photo: Three types of iron. Left: Pig iron is the raw material used to make other forms of iron and steel. Each of these iron pieces is one pig. Middle: Cast iron was used for strong, structural components like bits of engines and bridges before steel became popular. Right: Wrought iron is a softer iron once widely used to make everyday things like street railings. Today, wrought iron is more of a marketing description for what is actually mild steel (low-carbon steel), which is easily worked and shaped. Left photo by Alfred T. Palmer courtesy of US Library of Congress. Middle and right photos by explainthatstuff.com.

Strictly speaking, steel is just another type of iron alloy, but it has a much lower carbon content than cast and wrought iron and other metals are often added to give it extra properties. Steel is such an amazingly useful material that we tend to talk about it as though it were a metal in its own righta kind of sleeker, more modern "son of iron" that's taken over the family firm! It's important to remember two things, however. First, steel is still essentially (and overwhelmingly) made from iron. Second, there are literally thousands of different types of steel, many of them precisely designed by materials scientists to perform a particular job under very exacting conditions. When we talk about "steel", we usually mean "steels"; broadly speaking, steels fall into four groups: carbon steels, alloy steels, tool steels, and stainless steels. These names can be confusing, because all alloy steels contain carbon (as do all other steels), all carbon steels are also alloys, and both tool steels and stainless steels are alloys too.

Chart: Which countries produce the world's raw steel? Again, China utterly dominates. Approximately 1.8 billion metric tons of steel are made worldwide each year, and half of it comes from China. This chart shows estimated worldwide raw steel production figures for 2019 (inner ring) and 2018 (outer ring). In the United States, there were 98 "minimill" steel plants operating at the start of 2020 (down from 110 in 2018) making a total of about 111 million tons of steel (slightly down from 114 million tons in 2015). Indiana (26 percent), Ohio (12 percent), Michigan (5 percent), and Pennsylvania (5 percent) together produce about half of all US steel. Source: US Geological Survey, Mineral Commodity Summaries, January 2020.

The vast majority of steel produced each day (around 8090 percent) is what we call carbon steel, though it contains only a tiny amount of carbonsometimes much less than 1 percent. In other words, carbon steel is just basic, ordinary steel. Steels with about 12 percent carbon are called (not surprisingly) high-carbon steels and, like cast-iron, they tend to be hard and brittle; steels with less than 1 percent carbon are known as low-carbon steels ("mild steels") and like wrought iron, are softer and easier to shape. A huge range of different everyday items are made with carbon steels, from car bodies and warship hulls to steel cans and engine parts.

As well as iron and carbon, alloy steels contain one or more other elements, such as chromium, copper, manganese, nickel, silicon, or vanadium. In alloy steels, it's these extra elements that make the difference and provide some important additional feature or improved property compared to ordinary carbon steels. Alloy steels are generally stronger, harder, tougher, and more durable than carbon steels.

Tool steels are especially hard alloy steels used to make tools, dies, and machine parts. They're made from iron and carbon with added elements such as nickel, molybdenum, or tungsten to give extra hardness and resistance to wear. Tool steels are also toughened up by a process called tempering, in which steel is first heated to a high temperature, then cooled very quickly, then heated again to a lower temperature.

The steel you probably see most often is stainless steelused in household cutlery, scissors, and medical instruments. Stainless steels contain a high proportion of chromium and nickel, are very resistant to corrosion and other chemical reactions, and are easy to clean, polish, and sterilize. They're corrosion-proof because the chromium atoms react with oxygen in the air to form a kind of protective outer skin that stops oxygen and water from attacking the vulnerable iron atoms inside.

There are three main stages involved in making a steel product. First, you make the steel from iron. Second, you treat the steel to improve its properties (perhaps by tempering it or plating it with another metal). Finally, you roll or otherwise shape the steel into the finished product.

Most steel is made from pig iron (remember: that's an iron alloy containing up to 4 percent carbon) by one of several different processes designed to remove some of the carbon and (optionally) substitute one or more other elements. The three main steelmaking processes are:

Liquid steel made by one of these processes is cast into huge bars called ingots, each of which weighs anything from a couple of tons (in typical steel plants) to hundreds of tons (in really big plants making giant steel objects). The ingots are rolled and pressed to make three types of basic steel "building blocks" known as blooms (giant bars with square ends), slabs (blooms with rectangular ends), and billets (longer than blooms but with smaller square ends).

These blocks are then shaped and worked to make all kinds of final steel products. The basic shaping process usually involves hot rolling (for example, reheating blooms and then rolling them over and over again to make them thinner). Girders are made by rolling steel then forcing it through dies or milling machines to make such things as beams for buildings and railroad tracks. Rollers that are very close together can be used to squeeze steel into extremely thin sheets. Pipes are made by wrapping sheets round into circles then forcing the two edges together so they fuse under pressure where they join.

Shaped steel can be further treated in all kinds of ways. For example, "tins" for food containers (which are mostly steel) are made by electroplating steel sheets with molten tin using the process of electrolysis (the reverse of the electro-chemical process that happens in batteries). Steel that needs to be especially resistant to weathering can be galvanized (dipped into a hot bath of molten zinc so it acquires an overall protective coating).

In all this discussion of iron and steel, you'll have noticed that different types behave almost like completely different materials under different conditions. What makes one form of iron or steel different from another? Why are some very hard and brittle while others are relatively soft and malleable (easy to work)? Peer at the internal structure of iron or steel under an electron microscope and you'll see that the answer largely boils down to how much carbon the iron contains and how it's distributed. Iron and steel consist of grains made of different kinds of iron and carbon, some of which are hard, while others are soft. When the harder kinds predominate, you get a hard and brittle material; when there are more softer kinds in between, the material can bend and flex so you can work and shape it more easily.

Different types of iron and steel contain different amounts of these ingredients arranged in varying crystalline structures. Making iron alloys or steel by one method or another will change the relative amounts of the ingredients, altering its properties. Treating steel in different ways after it's made changes its physical properties by altering its internal crystalline structure. For example, heat-treating steel changes austenite inside it into martensite, making its internal structure very much harder. Hammering and rolling steel breaks up crystals of graphite and other impurities lurking inside it, closes up any gaps that could lead to weaknesses, and generally produces a more regular crystalline structure.

Steel is one of the most versatile materials, used in everything from jet engines to surgical instruments and from table knives to machine tools. Most modern buildings are "quietly" supported by a steel skeletona secret inner structurethat becomes invisible once they're complete. Major consumers of steel include the construction industry, the automobile and shipbuilding industries, producers of food cans, and manufacturers of electrical appliances.

Chart: What do we use steel for? Over two thirds (about 70 percent) is used for construction and transportation (mostly car-making) alone. Source: US Geological Survey, Mineral Commodity Summaries, January 2020.

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mining | britannica

mining | britannica

mining, process of extracting useful minerals from the surface of the Earth, including the seas. A mineral, with a few exceptions, is an inorganic substance occurring in nature that has a definite chemical composition and distinctive physical properties or molecular structure. (One organic substance, coal, is often discussed as a mineral as well.) Ore is a metalliferous mineral, or an aggregate of metalliferous minerals and gangue (associated rock of no economic value), that can be mined at a profit. Mineral deposit designates a natural occurrence of a useful mineral, while ore deposit denotes a mineral deposit of sufficient extent and concentration to invite exploitation.

When evaluating mineral deposits, it is extremely important to keep profit in mind. The total quantity of mineral in a given deposit is referred to as the mineral inventory, but only that quantity which can be mined at a profit is termed the ore reserve. As the selling price of the mineral rises or the extraction costs fall, the proportion of the mineral inventory classified as ore increases. Obviously, the opposite is also true, and a mine may cease production because (1) the mineral is exhausted or (2) the prices have dropped or costs risen so much that what was once ore is now only mineral.

Archaeological discoveries indicate that mining was conducted in prehistoric times. Apparently, the first mineral used was flint, which, because of its conchoidal fracturing pattern, could be broken into sharp-edged pieces that were useful as scrapers, knives, and arrowheads. During the Neolithic Period, or New Stone Age (about 80002000 bce), shafts up to 100 metres (330 feet) deep were sunk in soft chalk deposits in France and Britain in order to extract the flint pebbles found there. Other minerals, such as red ochre and the copper mineral malachite, were used as pigments. The oldest known underground mine in the world was sunk more than 40,000 years ago at Bomvu Ridge in the Ngwenya mountains, Swaziland, to mine ochre used in burial ceremonies and as body colouring.

Gold was one of the first metals utilized, being mined from streambeds of sand and gravel where it occurred as a pure metal because of its chemical stability. Although chemically less stable, copper occurs in native form and was probably the second metal discovered and used. Silver was also found in a pure state and at one time was valued more highly than gold.

According to historians, the Egyptians were mining copper on the Sinai Peninsula as long ago as 3000 bce, although some bronze (copper alloyed with tin) is dated as early as 3700 bce. Iron is dated as early as 2800 bce; Egyptian records of iron ore smelting date from 1300 bce. Found in the ancient ruins of Troy, lead was produced as early as 2500 bce.

One of the earliest evidences of building with quarried stone was the construction (2600 bce) of the great pyramids in Egypt, the largest of which (Khufu) is 236 metres (775 feet) along the base sides and contains approximately 2.3 million blocks of two types of limestone and red granite. The limestone is believed to have been quarried from across the Nile. Blocks weighing as much as 15,000 kg (33,000 pounds) were transported long distances and elevated into place, and they show precise cutting that resulted in fine-fitting masonry.

One of the most complete early treatments of mining methods in Europe is by the German scholar Georgius Agricola in his De re metallica (1556). He describes detailed methods of driving shafts and tunnels. Soft ore and rock were laboriously mined with a pick and harder ore with a pick and hammer, wedges, or heat (fire setting). Fire setting involved piling a heap of logs at the rock face and burning them. The heat weakened or fractured the rock because of thermal expansion or other processes, depending on the type of rock and ore. Crude ventilation and pumping systems were utilized where necessary. Hoisting up shafts and inclines was done with a windlass; haulage was in trucks and wheelbarrows. Timber support systems were employed in tunnels.

Great progress in mining was made when the secret of black powder reached the West, probably from China in the late Middle Ages. This was replaced as an explosive in the mid-19th century with dynamite, and since 1956 both ammonium nitrate fuel-blasting agents and slurries (mixtures of water, fuels, and oxidizers) have come into extensive use. A steel drill with a wedge point and a hammer were first used to drill holes for placement of explosives, which were then loaded into the holes and detonated to break the rock. Experience showed that proper placement of holes and firing order are important in obtaining maximum rock breakage in mines.

The invention of mechanical drills powered by compressed air (pneumatic hammers) increased markedly the capability to mine hard rock, decreasing the cost and time for excavation severalfold. It is reported that the Englishman Richard Trevithick invented a rotary steam-driven drill in 1813. Mechanical piston drills utilizing attached bits on drill rods and moving up and down like a piston in a cylinder date from 1843. In Germany in 1853 a drill that resembled modern air drills was invented. Piston drills were superseded by hammer drills run by compressed air, and their performance improved with better design and the availability of quality steel.

Developments in drilling were accompanied by improvements in loading methods, from handloading with shovels to various types of mechanical loaders. Haulage likewise evolved from human and animal portage to mine cars drawn by electric locomotives and conveyers and to rubber-tired vehicles of large capacity. Similar developments took place in surface mining, increasing the volume of production and lowering the cost of metallic and nonmetallic products drastically. Large stripping machines with excavating wheels used in surface coal mining are employed in other types of open-pit mines.

Water inflow was a very important problem in underground mining until James Watt invented the steam engine in the 18th century. After that, steam-driven pumps could be used to remove water from the deep mines of the day. Early lighting systems were of the open-flame type, consisting of candles or oil-wick lamps. In the latter type, coal oil, whale oil, or kerosene was burned. Beginning in the 1890s, flammable acetylene gas was generated by adding water to calcium carbide in the base of a lamp and then released through a jet in the centre of a bright metal reflector. A flint sparker made these so-called carbide lamps easy to light. In the 1930s battery-powered cap lamps began entering mines, and since then various improvements have been made in light intensity, battery life, and weight.

Although a great deal of mythic lore and romance has accumulated around miners and mining, in modern mining it is machines that provide the strength and trained miners who provide the brains needed to prevail in this highly competitive industry. Technology has developed to the point where gold is now mined underground at depths of 4,000 metres (about 13,100 feet), and the deepest surface mines have been excavated to more than 700 metres (about 2,300 feet).

expat dating in germany - chatting and dating - front page de

expat dating in germany - chatting and dating - front page de

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extracting gold | howstuffworks

extracting gold | howstuffworks

Removing the gold-bearing rock from the ground is just the first step. To isolate pure gold, mining companies use a complex extraction process. The first step in this process is breaking down large chunks of rock into smaller pieces. At a mill, large machines known as crushers reduce the ore to pieces no larger than road gravel. The gravel-like material then enters rotating drums filled with steel balls. In these drums, the ore is ground to a fine slurry or powder.

Next, mill operators thicken the slurry with water to form pulp and run the pulp through a series of leaching tanks. Leaching dissolves the gold out of the ore using a chemical solvent. The most common solvent is cyanide, which must be combined with oxygen in a process known as carbon-in-pulp. As the cyanide and oxygen react chemically, gold in the pulp dissolves. When workers introduce small carbon grains to the tank, the gold adheres to the carbon. Filtering the pulp through screens separates the gold-bearing carbon.

The carbon moves to a stripping vessel where a hot caustic solution separates the gold from the carbon. Another set of screens filters out the carbon grains, which can be recycled for future processing. Finally, the gold-bearing solution is ready for electrowinning, which recovers the gold from the leaching chemicals. In electrowinning, operators pour the gold-bearing solution into a special container known as a cell. Positive and negative terminals in the cell deliver a strong electric current to the solution. This causes gold to collect on the negative terminals.

Smelting, which results in nearly pure gold, involves melting the negative terminals in a furnace at about 2,100 degrees F (1,149 degrees C). When workers add a chemical mixture known as flux to the molten material, the gold separates from the metal used to make the terminals. Workers pour off the flux and then the gold. Molds are used to transform the liquid gold into solid bars called dor bars. These low-purity bars are then sent to refineries all over the world for further processing.

Major gold-producing countries include South Africa, the United States, Australia, Mexico, Peru, Canada, China, India and Russia. South Africa is the leading gold-producing country, followed by the United States and Australia. In the United States, Nevada is the leading gold producer.

uses of gold in industry, medicine, computers, electronics, jewelry

uses of gold in industry, medicine, computers, electronics, jewelry

Of all the minerals mined from the Earth, none is more useful than gold. Its usefulness is derived from a diversity of special properties. Gold conducts electricity, does not tarnish, is very easy to work, can be drawn into wire, can be hammered into thin sheets, alloys with many other metals, can be melted and cast into highly detailed shapes, has a wonderful color and a brilliant luster. Gold is a memorable metal that occupies a special place in the human mind.

Uses of Gold in the United States: This pie chart shows how gold was used in the United States in 2019, not including gold bullion. The main uses were in jewelry (50%) and electronics (37%). The minting of official coins accounted for 8% of the gold used, and 5% was for other uses. Data from the USGS Mineral Commodity Summaries for 2019.

When Spanish explorers first arrived in the "New World" they met the native people of South America. These two cultures had been separated by a vast ocean, they had never touched one another, they spoke different languages and lived entirely different lives. Yet they had one thing in common - they both held gold in highest esteem and used it to make some of their most important objects.

Throughout the history of our planet, almost every established culture has used gold to symbolize power, beauty, purity, and accomplishment. Today we continue to use gold for our most significant objects: wedding rings, Olympic medals, Oscars, Grammys, money, crucifixes and ecclesiastical art. No other substance of the same rarity holds a more visible and prominent place in our society.

Colors of gold-silver-copper alloys: Different metal colors that can be produced by alloying different amounts of gold, silver, and copper. Image by Metallos, used here under a GNU Free Documentation License.

Gold has been used to make ornamental objects and jewelry for thousands of years. Gold nuggets found in a stream are very easy to work and were probably one of the first metals used by humans. Today, most of the gold that is newly mined or recycled is used in the manufacture of jewelry. About 78% of the gold consumed each year is used in the manufacture of jewelry.

Special properties of gold make it perfect for manufacturing jewelry. These include: very high luster; desirable yellow color; tarnish resistance; ability to be drawn into wires, hammered into sheets, or cast into shapes. These are all properties of an attractive metal that is easily worked into beautiful objects. Another extremely important factor that demands the use of gold as a jewelry metal is tradition. Important objects are expected to be made from gold.

Pure gold is too soft to stand up to the stresses applied to many jewelry items. Craftsmen learned that alloying gold with other metals such as copper, silver, and platinum would increase its durability. Since then most gold used to make jewelry is an alloy of gold with one or more other metals.

The alloys of gold have a lower value per unit of weight than pure gold. A standard of trade known as "karatage" was developed to designate the gold content of these alloys. Pure gold is known as 24 karat gold and is almost always marked with "24K". An alloy that is 50% gold by weight is known as 12 karat gold (12/24ths) and is marked with "12K". An alloy that contains 75% gold by weight is 18 karat (18/24 = 75%) and marked "18K". In general, high-karat jewelry is softer and more resistant to tarnish, while low-karat jewelry is stronger and less resistant to tarnish - especially when in contact with perspiration.

Alloying gold with other metals changes the color of the finished products (see illustration). An alloy of 75% gold, 16% silver and 9% copper yields yellow gold. White gold is an alloy of 75% gold, 4% silver, 4% copper and 17% palladium. Other alloys yield pink, green, peach and even black-colored metals.

Because gold is highly valued and in very limited supply, it has long been used as a medium of exchange or money. The first known use of gold in transactions dates back over 6000 years. Early transactions were done using pieces of gold or pieces of silver. The rarity, usefulness, and desirability of gold make it a substance of long-term value. Gold works well for this purpose because it has a high value, and it is durable, portable, and easily divisible.

Some early printings of paper money were backed by gold held in safekeeping for every unit of money that was placed in circulation. The United States once used a "gold standard" and maintained a stockpile of gold to back every paper dollar in circulation.

Under this gold standard, any person could present paper currency to the government and demand in exchange an equal value of gold. The gold standard was once used by many nations, but it eventually became too cumbersome and is no longer used by any nation.

The gold used as a financial backing for currency was most often held in the form of gold bars, also known as "gold bullion." The use of gold bars kept manufacturing costs to a minimum and allowed convenient handling and storage. Today many governments, individuals, and institutions hold investments of gold in the convenient form of bullion.

The first gold coins were minted under the order of King Croesus of Lydia (a region of present-day Turkey) in about 560 BC. Gold coins were commonly used in transactions up through the early 1900s, when paper currency became a more common form of exchange. Gold coins were issued in two types of units. Some were denominated in units of currency, such as dollars, while others were issued in standard weights, such as ounces or grams.

Today gold coins are no longer in wide use for financial transactions. However, gold coins issued in specific weights are popular ways for people to purchase and own small amounts of gold for investment. Gold coins are also issued as "commemorative" items. Many people enjoy these commemorative coins because they have both a collectible value and a precious metal value.

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The most important industrial use of gold is in the manufacture of electronics. Solid state electronic devices use very low voltages and currents which are easily interrupted by corrosion or tarnish at the contact points. Gold is the highly efficient conductor that can carry these tiny currents and remain free of corrosion. Electronic components made with gold are highly reliable. Gold is used in connectors, switch and relay contacts, soldered joints, connecting wires and connection strips.

A small amount of gold is used in almost every sophisticated electronic device. This includes cell phones, calculators, personal digital assistants, global positioning system (GPS) units, and other small electronic devices. Most large electronic appliances such as television sets also contain gold.

One challenge with the use of gold in very small quantities in very small devices is loss of the metal from society. Nearly one billion cell phones are produced each year, and most of them contain about fifty cents worth of gold. Their average lifetime is under two years, and very few are currently recycled. Although the amount of gold is small in each device, their enormous numbers translate into a lot of unrecycled gold.

Gold is used in many places in the standard desktop or laptop computer. The rapid and accurate transmission of digital information through the computer and from one component to another requires an efficient and reliable conductor. Gold meets these requirements better than any other metal. The importance of high quality and reliable performance justifies the high cost.

Edge connectors used to mount microprocessor and memory chips onto the motherboard and the plug-and-socket connectors used to attach cables all contain gold. The gold in these components is generally electroplated onto other metals and alloyed with small amounts of nickel or cobalt to increase durability.

How would iron work as a dental filling? Not very well... your dentist would need blacksmithing tools, your smile would be rusty a few days after a filling, and you would need to get used to the taste of iron. Even at much higher expense, gold is used in dentistry because of its superior performance and aesthetic appeal. Gold alloys are used for fillings, crowns, bridges, and orthodontic appliances. Gold is used in dentistry because it is chemically inert, nonallergenic, and easy for the dentist to work.

Gold is known to have been used in dentistry as early as 700 B.C. Etruscan "dentists" used gold wire to fasten replacement teeth into the mouths of their patients. Gold was probably used to fill cavities in ancient times; however, there is no documentation or archaeological evidence for this use of gold until a little over 1000 years ago.

Gold was much more generously used in dentistry up until the late 1970s. The sharp run-up of gold prices at that time motivated the development of substitute materials. However, the amount of gold used in dentistry is starting to rise again. Some motivation for this comes from concerns that less inert metals might have an adverse effect on long-term health.

Gold is used as a drug to treat a small number of medical conditions. Injections of weak solutions of sodium aurothiomalate or aurothioglucose are sometimes used to treat rheumatoid arthritis. Particles of a radioactive gold isotope are implanted in tissues to serve as a radiation source in the treatment of certain cancers.

Small amounts of gold are used to remedy a condition known as lagophthalmos, which is an inability of a person to close their eyes completely. This condition is treated by implanting small amounts of gold in the upper eyelid. The implanted gold "weights" the eyelid, and the force of gravity helps the eyelid close fully.

Radioactive gold is used in diagnosis. It is injected in a colloidal solution that can be tracked as a beta emitter as it passes through the body. Many surgical instruments, electronic equipment, and life-support devices are made using small amounts of gold. Gold is nonreactive in the instruments and is highly reliable in the electronic equipment and life-support devices.

If you are going to spend billions of dollars on a vehicle that when launched will travel on a voyage where the possibility of lubrication, maintenance and repair is absolutely zero, then building it with extremely dependable materials is essential. This is exactly why gold is used in hundreds of ways in every space vehicle that NASA launches.

Gold is used in circuitry because it is a dependable conductor and connector. In addition, many parts of every space vehicle are fitted with gold-coated polyester film. This film reflects infrared radiation and helps stabilize the temperature of the spacecraft. Without this coating, dark colored parts of the spacecraft would absorb significant amounts of heat.

Gold is also used as a lubricant between mechanical parts. In the vacuum of space, organic lubricants would volatilize and they would be broken down by the intense radiation beyond Earth's atmosphere. Gold has a very low shear strength, and a thin film of gold between critical moving parts serves as a lubricant - the gold molecules slip past one another under the forces of friction and that provides a lubricant action.

What metal is used to make the crown worn by a king? Gold! This metal is selected for use because gold is THE metal of highest esteem. It would make no sense to make a king's crown out of steel - even though steel is the strongest metal. Gold is chosen for use in a king's crown because it is the metal associated with highest esteem and status.

Gold is associated with many positive qualities. Purity is another quality associated with gold. For this reason, gold is the metal of choice for religious objects. Crosses, communion ware, and other religious symbols are made with gold for this reason.

Gold is also used as the first place winner's medal or trophy in almost any type of contest. First-place winners at the Olympic Games are given gold medals. The Academy Awards Oscars are gold awards. Music's Grammy Awards are made of gold. All of these important achievements are honored with awards made of gold.

Gold has many uses in the production of glass. The most basic use in glassmaking is that of a pigment. A small amount of gold, if suspended in the glass when it is annealed, will produce a rich ruby color.

Gold is also used when making specialty glass for climate-controlled buildings and cases. A small amount of gold dispersed within the glass or coated onto the glass surface will reflect solar radiation outward, helping the buildings stay cool in the summer, and reflect internal heat inward, helping them stay warm in winter.

The visor on the helmet of an astronaut's space suit is coated with a very thin film of gold. This thin film reflects much of the very intense solar radiation of space, protecting the astronaut's eyes and skin.

Gold has the highest malleability of any metal. This enables gold to be beaten into sheets that are only a few millionths of an inch thick. These thin sheets, known as "gold leaf" can be applied over the irregular surfaces of picture frames, molding, or furniture.

Gold leaf is also used on the external and internal surfaces of buildings. This provides a durable and corrosion-resistant covering. One of the most eye-catching uses of gold leaf is on the domes of religious buildings and other important structures. The cost of this "roofing material" is very high per square foot; however, the cost of the gold is only a few percent of the total project cost. Most of the cost goes to the labor of highly skilled artisans who apply the gold leaf.

Gold is too expensive to use by chance. Instead it is used deliberately and only when less expensive substitutes cannot be identified. As a result, once a use is found for gold it is rarely abandoned for another metal. This means that the number of uses for gold have been increasing over time.

Most of the ways that gold is used today have been developed only during the last two or three decades. This trend will likely continue. As our society requires more sophisticated and reliable materials, our uses for gold will increase. This combination of growing demand, few substitutes, and limited supply will cause the value and importance of gold to increase steadily over time. It is truly a metal of the future.

Because of its rarity and high price, manufacturers are always looking for ways to reduce the amount of gold required to make an object or substitute a less expensive metal in its place. Base metals clad with gold alloys have long been used as a way to reduce the amount of gold used in jewelry and electrical connections. These items are constantly being redesigned to reduce the amount of gold required and to maintain their utility standards. Palladium, platinum, and silver are the most common substitutes for gold that closely retain its desired properties.

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