Silver mining is the extraction of silver from minerals, starting with mining. Because silver is often found in intimate combination with other metals, its extraction requires elaborate technologies. In 2008, ca. 25,900 metric tons were consumed worldwide, most of which came from mining.
Silver sources
Silver-bearing ore typically contains very little silver, with much higher percentages of copper and lead. Specific minerals include argentite (Ag2S), chlorargyrite ("horn silver," AgCl), polybasite (Ag, Cu)16Sb2S11), and proustite (Ag3AsS3). Silver mainly occurs as a contaminant in chalcopyrite and galena, important ores of copper and lead, respectively.
Some ores are actually mined explicitly for their silver value vs the silver being a byproduct of other metals. However silver is only found rarely in a native form as nuggets, in placer deposits, and veins.
Excavation
Methods for mining silver depend on the grade of the ore, its depth, host rock, and other economic factors. Commonly, silver ore is obtained from open pit mines, and underground drifts and shafts. Explosives are frequently used to shatter veins into manageable pieces, which are transported via mine cars and then lifted to the surface. The process can be dangerous.
Ore processing
Once removed from the mine, silver-containing ore is crushed (comminution) into a fine powder to expose individual grains to chemical processing. As a byproduct of mining of lead and copper, silver ores are often purified by froth flotation. After froth flotation, silver is extracted by a cyanide process, akin to technology used for gold extraction. In some cases, the ore is treated by smelting before cyanide treatment. Silver is also produced during the electrolytic refining of copper and by application of the Parkes process on lead ores. Commercial grade fine silver is at least 99.9 percent pure silver, and purities greater than 99.999 percent are available.
Recycling
About 5000 tons of silver are annually recovered from scrap. Jewelry, photographic film, silverware, coins, electronics are sources of recyclable silver.
Production areas
The principal sources of silver are copper, copper-nickel, gold, lead, and lead-zinc ores obtained from Canada, Mexico, Poland, Peru, Bolivia, Australia and the United States.
Mexico was the world's largest silver producer in 2014, producing 5,000 metric tons (161 million troy ounces), 18.7 percent of the 26,800 tonne (862 million troy ounce) production of the world.
History
Silver mining has been undertaken since as early as the 5th century BCE. As silver is a precious metal often used for coins and bullion, its mining has historically often been lucrative. As with other precious metals such as gold or platinum, newly discovered deposits of silver ore have sparked silver rushes of miners seeking their fortunes. In recent centuries, large deposits were discovered and mined in the Americas, influencing the growth and development of Mexico, Andean countries such as Bolivia, Chile and Peru, as well as Argentina, Canada and the United States.
Silver has been known since ancient times. Silver is mentioned in the Book of Genesis, and slag heaps found in Asia Minor and on the islands of the Aegean Sea indicate that silver was being separated from lead as early as the 4th millennium BC. The silver mines at Laurium were very rich and helped provide a currency for the economy of ancient Athens, where the process involved mining the ore in underground galleries, washing and then smelting it to produce the metal. Elaborate washing tables still exist at the site which used rain water held in cisterns and collected during the winter months.
The Romans took over silver mining in Spain from Carthage after their acquisition of Carthaginian territories there following the Second Punic War. Extraction of silver from lead ore was widespread in Roman Britain very soon after the Roman conquest of the first century AD.
One of the main aims of the Viking expansion throughout Europe was to acquire and trade silver. Bergen and Dublin are still important centres of silver making. An example of a collection of Viking-age silver for trading purposes is the Galloway Hoard.
From the mid-15th century silver began to be extracted from copper ores in massive quantities using the liquation process creating a boost to the mining and metallurgy industries of Central Europe.
