Gold, silver and bronze: where do these metals come from?

Hand Holds Up a Bunch of Gold Medals © iStockPeskyMonkey

Gold medals can be won or lost within fractions of seconds; Bradley Wiggins' bike frame is made of 'nanoalloy carbon', Andy Murray uses a graphite tennis racket and Jessica Ennis' running spikes use the latest carbon and nano-ceramics technologies.

However, the technologies used to mine and process the metals used for winners' medals have been around for much longer, but which countries dominate the production of gold, silver and bronze?

The metals used to produce the medals at the London 2012 Olympic and Paralympic Games were exclusively provided by Rio Tinto; from its mines in Australia, Mongolia and the USA.

Gold

Characteristics

Figure 1: Country share of world gold production (%) in 2010. (Source: BGS World Mineral Statistics)

Gold (Au) is a precious metal and has been mined since the ancient Egyptian times; whilst smelting and fusing of gold-rich ores has been reported since 3600 BC.

Gold occurs in many different rock types and geological environments and economic deposits are mainly of two types: lode deposits and placer deposits. Gold is often associated with other base-metal ores and recovered during the smelting/ refining stages.

Depending on the geological setting of a deposit, gold is extracted by open pit or underground mining methods.

Following extraction, ore goes through crushing and grinding stages and appropriate size ore particles are then fed into the cyanidation process, which is responsible for extracting gold from the ore. Sometimes, further concentration of the ore is required (e.g. if sulphides are present) and flotation stages are then included.

Gold extracted from the ore is purified by smelting and gold is moulded into bars known as doré. The doré bars are then sent to refineries, where remaining impurities are removed to create gold of 99.5 per cent purity or greater. The purity of gold in an alloy is measured in carats, with pure gold being of 24 carats.

World production of gold

Figure 2: Five-year trend of gold production for major producers. Source: (Source: BGS World Mineral Statistics)

Over 90 countries now produce gold worldwide and there are several additional small operations that produce substantial amounts of gold, but these figures are not commonly recorded in official statistics (for example, artisanal mining).

According to the BGS world mineral production data, the production figure for gold in 2010 was nearly 2.3 million kg (metal content). Major gold producers and production market trends over five years are presented in Figure 1 and Figure 2.

China remains the largest producer of gold with a 14 per cent share of the global production. However, Figure 1 clearly demonstrates that gold is produced by numerous countries in significant quantities, which makes it a global commodity.

According to the World Gold Council, the value of gold has increased by 120 per cent over the last three years. The investment sector has presented a significant growth, but demand from the jewellery and technology sectors has also contributed to recent high gold prices.

End markets for gold

The jewellery market is perceived as the major consumer for gold (approximately 59 per cent of the world production), but it is not the only market. The investment sector and central bank reserves are also key markets for gold (around 29 per cent of the world production). The technology sector is increasingly using gold (the remaining 12 per cent of the world production) and it finds application in the following end uses:

  • automotive industry: in catalytic convertors
  • electronics: in mobile phones, computer systems and other high performance electronic applications
  • engineering: as a lubricator; in fuel cells; in jet engines
  • medicine: in dentistry and other novel medical treatments (e.g. implants, rheumatoid arthritis)
  • nanotechnology: chemical catalysts and diagnostic devices
  • space technology and exploration

Secondary sources and recycling of gold

Gold is also recovered from secondary sources, such as high-grade scrap jewellery and scrap dental appliances, or lower grade scrap from electronic waste. Gold scrap is fed into refineries to recover the gold. The recovery of gold from secondary sources is often governed by the market trends and price of gold metal.

Silver

Characteristics

Figure 3: Country share of world silver production (%) in 2010. (Source: BGS World Mineral Statistics)

Silver (Ag) is also a precious metal, and mining has been reported some 5000 years ago. Silver is soft and ductile; due to these properties silver is used in several applications including jewellery and various industrial uses.

Silver is mined from lode and placer deposits and is often co-mined with gold and suphide ores (copper, lead and zinc). Most of the silver is recovered from sulphides. The ore goes through various stages of comminution, followed by froth flotation, where metal concentrates are collected.

Copper and lead concentrates are sent to smelters for the production of crude metals. Zinc concentrates are roasted and the silver-rich calcine residue is sent to a lead smelter for further processing.

Gold-silver ores undergo leaching treatment. Silver doré is produced from these processes and they are refined further by electrolysis to produce silver bars. Pure silver is of 999 fineness.

World production of silver

Figure 4: Country share of world silver production (%) in 2010. (Source: BGS World Mineral Statistics)

Silver is produced from approximately 60 producers worldwide, with Mexico being the lead producer. In 2010, world silver production accounted for nearly 23.8 million kg (metal content).

Overall, silver mine production rose significantly over the last few years and in 2011 demand for silver reached its second highest level since 20001.

1The Silver Institute – Silver demand

End markets

Silver is used in industrial applications, in jewellery and silverware, in coins and medals and has a strong presence in the investment market.

Silver use in industry and technology has shown a significant increase in recent years and it now represents the major end user. Silver is being used by the following industry sectors:

  • automotive: in silver coated contacts, silver membrane switches and other applications
  • battery manufacture: for the production of silver cell batteries
  • brazing and soldering: for the manufacture of AgCu alloys
  • chemical industry: as a catalyst in ethylene oxide plants
  • electrical and electronics: due to its high electrical conductivity it finds widespread use, such as for the production of light and heavy duty switches, in printable electronics (e.g RFID tags), and various silver pastes
  • green technologies: for example, in photovoltaic manufacture, in water purification processes, in thermal windows and others
  • medicine: due to its antibacterial properties and in X-ray technology
  • nanotechnology: for the production of nanosilver

The demand for silver jewellery has remained high. However, the silverware and photography markets have been in decline.

A variety of silver investment options exist and they have presented a significant growth over the last few years. This is due to its long-lasting value, wealth and the provision of stability in comparison to other investment outlets, such as stocks.

Recycling

Silver is found in various waste streams, such as waste from electrical and electronic equipments (WEEE), scrap metals, spent catalysts, jewellery and silverware waste, spent plating solutions and photographic waste.

Processes for recovering silver are well established for certain waste materials (e.g photographic waste and jewellery scrap) and continues to improve for newer streams, such as WEEE.

Bronze

Characteristics

Bronze is a copper and tin alloy, but the term is also used for a variety of copper alloys, some of which do not contain tin at all.

The use of bronze has been reported since the earliest Mesopotamian and Egyptian civilisations in the manufacture of tools and weapons. Bronze contains around 90 per cent copper and up to 10 per cent tin, occasionally more depending on the end use.

Copper is a semi-precious metal and some of its key characteristics include ductility, malleability, thermal and electrical conductivity, resistance to corrosion and antimicrobial characteristics.

The addition of tin improves the wear resistance of copper. Further information on copper can be found in the BGS Copper Mineral Profile.

Other elements, such as phosphorus, aluminium, lead, nickel and others are often added to produce an extensive range of bronze alloys that find application in different end uses.

World production copper and tin

Over 50 countries produce copper and around 20 countries produce tin worldwide.

Chile represents the largest producer of copper, whilst China accounts for approximately 50 per cent of world tin production. Although Chile accounts for a significant share of the global production, copper deposits are dispersed around the world. Tin deposits on the other hand are concentrated in East Asia and South America, with Australia being the only other producing country.

Copper; major producers 2010
Copper; major producers 2010

Figure 7.   Five-year trend of copper production for major producers. Source: (Source: BGS World Mineral Statistics)
Figure 8.  Five-year trend of tin production for major producers. Source: (Source: BGS World Mineral Statistics)

End uses

Bronze is used in a number of products, including bearings, springs, bushings, steam pressure castings, automobile transmissions, clips, for ornamental uses, in musical instruments and medals.

Recycling

Copper and copper alloys such as bronze are widely recycled and production of secondary copper from scrap accounts for two thirds of total copper production.

Bronzes can be perpetually recycled without any adverse effects on their composition. Scrap bronze is collected from processing residues (slag, drosses, fines) and post-consumer waste (end of life vehicles, construction and demolition waste, waste electrical and electronic equipment or WEEE).

Recycling includes the collection; segregation and melting of scrap metal in smelters most of the time, but modification to the above processes may occur if scrap of lower purity is collected.

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