Mining for silver, like many mining operations, is a challenging, capital intensive and high-risk area of activity. If you are thinking of investing in silver, this article explains how silver is mined and refined; and it also summarises the locations of the main silver mining regions and who the major producers are.
How the mining for silver process works?
Silver is often mined alongside other metals such as gold and often occurs with lead, copper and zinc ores. The mining methods vary depending on the type of rock formations and their characteristics, though both open pit and underground methods are used.
How is silver refined?
Silver usually occurs combined with lead or copper, though the silver concentration in the ore is often much less than one per cent.
Only a quarter of silver comes from ores explicitly mined for their silver content; the rest is extracted from ores mined primarily for lead, copper or zinc. All these metals are found in combination with sulphur as metal sulphides.
In the early days silver was refined by smelting and cupellation. Later, when the Spanish discovered much richer silver mines in Mexico, Peru and Bolivia, they used the Patio process.
The process is attributed to a mining specialist – Bartolomé de Medina who was the first to use a silver amalgamation with mercury to extract silver.
De Medina’ s technique involved mixing the ore with mercury and strong brine. This formed a mercury silver amalgam from which semi-pure silver could be obtained by distilling off the mercury.
Further refinement was achieved by cupellation. During the late 19th Century, the Patio process was replaced by cyanidation and electrorefining.
The method used for refining silver depends on the kind of ore:
- Copper sulphides: smelting creates blister copper that retains most of the silver (up to 99%). The copper is electrolytically refined causing a silver-rich reside to form containing up to 20% silver.
- On smelting, all metals apart from silver, gold, and platinum-group metals are removed. The metal mix is used to produce electrodes which are electrolysed in silver copper nitrate to produce up to 99.99% pure silver.
- Lead concentrates are roasted and smelted to remove various impurities then zinc is added to melted lead bullion.
- Gold and silver compounds float to the top and are skimmed off. The zinc is then distilled off, and various processes are used to separate the gold and the silver.
- Zinc concentrates are leached with sulphuric acid to leave a silver, gold, lead residue. This is melted and treated with air, and powdered coal and the resulting bullion is refined as above.
Where are the major silver mining regions?
Today, most of the world’s silver comes from Mexico, Bolivia, Turkey, Canada, USA, Norway, Peru, and Poland. Mexico is the biggest producer. The world’s ten largest silver mines are:
- Penasquito, Mexico: operated by Goldcorp, the mine has an estimated 900 million ounces of silver reserves.
- Polkowice-Sieroszowice, Poland: operated by state-owned mining enterprise KGHM, its silver reserves are estimated as 700 million ounces.
- San Cristobal, Bolivia: operated by Minera San Cristobal (MSC), a subsidiary of the Sumitomo Corporation of Japan, it has approximately 500 million ounces of silver reserves.
- Pitarrilla, Mexico: operated by Silver Standard of Vancouver is has estimated silver reserves of 470 million ounces
- Lubin, Poland: has an estimated 442.4 million ounces of silver reserves. It is also owned and operated by KGHM.
- Rudna, Poland: is another KGHM mine and has around 350 million ounces silver reserves
- Gumuskoy, Turkey: operated by Turkish state-owned mining company Eti Mine Workshas, it has approximately 335 million ounces silver reserves
- Fresnillo, Mexico: has approximately 300 million ounces silver reserves. The mine is operated by Fresnillo plc.
- Antamina, Peru: is a joint venture between BHP Billiton, Xstrata, Teck, and Mitsubishi Corporation. It has an estimated 280 million ounces silver reserves
- Cannington, Australia: owned by BHP Billiton, it has about 215 million ounces silver reserves.
Who are the main silver producers?
- Fresnillo plc, Mexico: produces 54.2 million ounces silver making it the world’s largest silver producer. It is also the second largest gold producer.
- KGHM, Poland: produces 40.0 million ounces silver, though its main business is copper production
- Goldcorp Inc., Canada: produces 28.6 million ounces though its main business is gold production
- Polymetal International plc, Russia: produces 26.8 million ounces silver
- Compania de Minas Buenaventura S.A.A., Peru: produces 26.4 million ounces silver
- Pan American Silver Corp., Canada: produces 25 million ounces silver plus gold, zinc, lead, and copper
- Hochschild Mining plc, United Kingdom: produces 19.1 million ounces silver plus gold with mines in Peru and Argentina.
- Volcan Compania Minera S.A.A., Peru: produces 17.3 million ounces silver plus zinc, lead, and copper
- Hindustan Zinc Ltd., India: produces 16.9 million ounces silver though it is the world’s largest zinc producer.
Investing in silver
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