Silver Mining & Metallurgy

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Silver Metallurgy

Rare native silver protruding from a galena-baryte host which in itself would be an ore for silver

Contrary to gold, silver occurring in a pure metallic form is extremely rare in nature. Most silver occurs in ores containing a mix of metals, most commonly lead, zinc, nickel and/or copper. As a consequence these ores have to undergo some sort of refining in order to extract the pure silver.

This wasn't any different in the Bronze Age. You have got to give it to these early metallurgists, they were very resourceful. As early as the early third millennium silver was extracted from lead ores by means of a complicated process. First the ores had to be heated in a reducing atmosphere so that the metals are extracted from their base rock and form an alloy, a process called 'smelting'.

Smelting is more than just 'melting the metal out of its ore'. Most silver ores are a chemical compound of several metals bound to other elements, such as oxygen (as an oxide), sulfur (as a sulfide) or carbon and oxygen together (as a carbonate).
A furnace with bellows, 16th century
In order to get rid of the sulfur and carbon the ores have to be crushed and then 'roasted' which means that they are heated for prolonged periods of time under moderate temperatures. This happens in an oxidizing environment so that the sulfur and carbon react with the oxygen and are driven off as the gases carbon dioxide and sulfur dioxide. The roasting will leave us with our metals bound to oxygen only. The next step is to get the oxygen to free the metal.

In order to achieve this these oxides have to be heated to high temperatures in a reducing atmosphere. This means that the flow of oxygen is eliminated or, at least, limited in the furnace while the metal is surrounded by an element that readily binds with oxygen, such as carbon in the form of charcoal. When this is performed properly the oxides will undergo a chemical reaction. The oxygen from the oxides will form carbon dioxide with the carbon provided by the charcoal and the metals will form a metallic alloy.

Finally, this alloy has to be 'cupelled'. The result of this method is an almost pure silver as long as no gold was present in the ore. Ancient silver does contain trace elements, typically lead, gold, bismuth and other metals and measuring the concentrations of these 'impurities' can help the forensic jewelry historian in determining the authenticity of classical items.

The general process of mining-crushing-roasting-reducing-cupelling lead-silver ores remained the main method of silver extraction for thousands of years. It wasn't until halfway through the 15th century that liquation started to be used to extract silver from silver-copper ores. This technique has been extensively used in Central Europe from the Middle Ages until the late 19th century. In order to separate the silver from the copper the ore is first melted while adding lead. Silver has a higher affinity to lead than copper so will bond with the lead. After melting the ore a few times so that most of the silver has teamed up with lead rather than with the copper the mix is heated to above the melting point of lead but below that of copper. The silver-rich lead can then be drained off, leaving behind pure copper, and cupelled to separate the two metals.

An albumen print of the Patio Process at the Gould & Curry Mill at the Comstock Lode, Nevada, 1866
In 1554 mercury amalgamation started to be used. The discovery of mercury amalgamation has been attributed to a Spanish merchant, Bartolomé de Medina, who was the first to apply the technique to silver ores in Spanish America. The method comprises the crushing of the ore to a fine powder and then mixing it with salt, water, copper sulphate and mercury in a basin in which it is left for prolonged periods of time while being stirred constantly. This causes the silver to form an alloy with the mercury: a so-called amalgam. This would be separated from the rest of the sludge and then heated in order to drive off the mercury, leaving the miner with pure silver. This process is better known as the Patio Process, later improved to become the Pan Amalgamation Process.

These days electrowinning by making use of electrolysis has replaced the amalgamation process as has the Parkes Process.

Silver Mining

Bronze Age - Turkey and Armenia

When silver mining truly started isn't known exactly but slag heaps in modern day Turkey and Armenia indicate that some silver extraction from lead ores must have been occurred here as early as the 4th millennium BC. From here silver refining technology spread to the rest of Asia Minor and Europe.

Classic Era - Greece and Spain

As written above, the main occurrence of silver is in lead ores. The first real silver mining areas, those of Anatolia (Turkey, from around 2500BC ) and later Laurium (Greece, from around 1000BC) formed no exception. Since high doses of lead inevitably will kill those who are exposed to it, silver mining soon became a sector driven by slaves, something which remained the case for many centuries. The Phoenicians, a sea faring and trading culture originally from the Lebanese and Syrian coasts discovered the Spanish deposits around the year 800BC. By 700 BC their explorations yielded that much silver that it depressed the value of silver bullion in the entire Classical world.

Having access to silver deposits and being able to mine them played a big role in the classical world. Silver was used as a currency in Athens since 580BC so being able to mine it literally contributed to the wealth of the city. Many historians have argued that it was the possession and exploitation of the Laurium mines by the Athenians that allowed them to become the most powerful city state in Greece (see map in next section of this article for the location of these mines).

Worker.jpg
The Athenians were well aware of the significance of the mining operations to the prosperity of their city. This becomes obvious from studying records that show many citizens had shares in the mines. In 512BC the Persians overran the silver mines in northern Greece, leaving the Athenians to depend solely on the mines at Laurium, something which triggered an increase in further exploration of the deposit. In 483-482 BC a large new vein was found at the site and the Athenian leader Themistocles persuaded the citizens to forgo their usual dividend from the mine so that the city could use the money to build a large fleet. A fleet which would make the difference at the battle of Salamis where it defeated the Persian one, averting general defeat and paving the way for domination of Ancient Greece.

As big a role as the Laurium mines played in the uprise of Athens in the 5th century BC, an even so big role they played in the downfall of the city state. When, during the Peloponnesian War, the Spartans stationed an army near Athens the slaves which worked the mines fled amass. Athens got cut-off from its war fund and eventually lost the war to Sparta. The Laurium mines were worked for some time after that but eventually got depleted and the main Greek silver production shifted to mines in Macedonia.

Roman Water Wheel photo A.jpg
For the Romans, whose stability of currency also depended mainly on silver, the mines in Spain's southeast became the main source of the metal. These mines, initially exploited by the Roman arch enemy Carthage after the First Punic War, fell into Roman hands after the defeat of Carthage in the Third Punic war and enabled Rome to further expand its empire. When, in 55BC, the Romans invaded Britain they were quick to discover and exploit the lead-silver deposits there. Only six years later they had established many mines and Britain became another major source of silver.

Middle Ages - Central Europe

The demise of the Roman Empire caused havoc and destruction to the whole of Europe and consequently organized silver mining of a scale practiced in Classical times became impossible. From around the 8th century AD silver mining in Europe picked up again, especially in Central Europe resulting in more intensive mining during the rest of the Middle Ages.

1500-1800 - South and Central America

Silver mining at Potosí, Bolivia, 17th century
The discovery of America in 1492 heralded major changes in the magnitude of the world's silver production. In 1546 the Potosí mines in Bolivia and the Cerro de la Bufa mines in Mexico were discovered. Both deposits contained vast amounts of silver, quantities of ore which were unheard of in Europe. Over the centuries after 'the Conquest' numerous other deposits were located and mined in South and Central America, fueling the treasury of the Spanish crown and enabling it to lead a dominating role in Europe.

One of the most remarkable localities in the Americas was that which became known as Planchas de Plata near what is now Nogales at the border of Mexico and the US. Here native silver, and a fair bit of it too, was found in placers. There have been reports of slabs weighing more than 2500 pounds!

1800-1900 - North America

The first silver deposit in the USA was found in North Carolina, northeast of Charlotte. Named Silver Hill for obvious reasons this deposit was worked from 1838 on. Some 20 years later gold prospectors mining a gold placer in western Nevada were annoyed by what they called 'blue mud'. The sticky clay was a nuisance to these men, clogging their sluices and making getting around a hard task. In 1859 a rancher by the name of B.A. Harisson sent a sample of this blue mud to an assayer in California who found out that it was loaded with silver, over $3000 of it per ton! The richest silver ore ever found was being thrown away by men desperately looking for a few flakes of gold.

As soon as the news spread claims were staked and silver mining at what has become known as the 'Comstock Lode' began. Miners moved to the area in great numbers and settled in what would become Virginia City. In 1863 this was a bustling town counting 10.000 residents. For the next 20 years this deposit yielded enormous amounts of silver.

Comstock-Lib-Cong-LC-USZ62-03.jpg

Although it is mainly the Gold rushes that have become famous, silver often has left a much deeper footprint in the history of the areas it was mined in than gold has. A typical gold rush would last anywhere from a few months to a few years but after the alluvial gold was mined prospectors would leave the area, leaving their make-shift structures behind to become ghost towns. Silver regions however, would see a much longer habitation since the metal isn't mined from placer deposits but has to be extracted from ores which lie at greater depths and occur in greater quantities. Because silver mining towns would see prosperity for several decades rather than a few years they could develop into more complex and further advanced communities, thus giving the towns a greater chance of survival after the silver had been mined out. This is not only true for just the mining towns but also for ports close by. Take San Francisco for example, which wasn't just built on gold from the Sierra's, but to a large extend on silver from the Comstock Lode. In terms of an effect on the civilization of an area, gold has played a much lesser role than silver.

Silver can further pride itself with a huge effect on technological advances in the field of mining. Gold mining, until recent times, has often been a surface engagement. Since miners would just extract the gold from placer deposits rudimentary techniques were sufficient. How different it was for silver miners. Silver-lead ores, often occurring in veins, would be chased to great depths, thus posing miners with every problem imaginable. The solutions to these problems changed mining indefinitely. Techniques first applied in silver mines proved to aid the entire industry and these technological novelties were soon applied in other mining sectors. A great example of this is the so called honey comb structure method of supporting large ball rooms (the word used by miners to indicate large underground chambers, see image above). This method is said to have been invented by a miner working the Comstock Lode in Nevada who got his inspiration from looking at bees while pondering on how to prevent further cave-ins.

1900-Present

Over the last century mining technology and extraction methods greatly benefited from the invention of electricity and the combustion engine. These days silver mining has become a highly advanced sector. The top five silver producing countries in 2010 were Mexico, Peru, China, Australia and Chile. Other major producers are Bolivia, the USA, Poland, Russia Argentina and Canada.

Silver Mine Locations & Timeline

The map below lists the most important mines in the history of silver mining. Click on the markers for more info and dates of discovery.

<googlemap version="0.9" lat="31.353637" lon="11.953125" zoom="1" width="700" height="400" controls="small" icon="http://www.langantiques.com/university/images/2/25/Silvermarker.png"> 37.721578, 24.037399 Laurium - Major source of silver in classical times. The silver deposits of here boosted the Athenian economy immensely. 38.653343, 34.849663 Anatolia, modern day Turkey - This is where silver extraction through cupellation is said to have been invented. Archaeological evidence suggests that silver was extracted from argentiferous lead ores as early as the 4th millennium BC. 51.294559, -2.755337 Charterhouse - Roman Lead-Silver mines. 52.596375, -2.982788 Shropshire - Roman lead-silver mine. 53.134826, -1.564522 Matlock - Roman lead - silver mine. 53.230906, -3.208351 Halkyn Mountain - Roman Lead-Zinc-Silver mine. 22.778872, -102.560978 Cerro de la Bufa - First silver find in Mexico - 1546 54.26382, -4.467316 Isle of Man - Highly argentiferous lead mines. 50.32245, -5.016632 Cornwall - Argentiferous lead ores 59.659417, 9.624023 Kongsberg, Norway - Worked since 1623 - These mines are situated in Gneiss and crystalline slate. The silver occurs in parallel belts of rock impregnated with sulphides of iron, copper, zinc, lead, cobalt and silver 59.778522, 14.523926 Hallefors, Sweden - Historical Silver locality - in working in 1767 59.927496, 16.600342 Sala, Sweden - Most important Swedish silver mining locality from highly argentiferous galena. This mine is expected todate back well into the early Middle Ages, perhaps even earlier. 48.708182, 18.92395 Kremnitz - Slovakia - Medieval Silver mines 48.73989, 19.118958 Neusohl, Slovakia - Silver locality since the Middle Ages 48.458352, 18.900604 Schemnitz, Slovakia - Silver mines since the Middle Ages. 44.737954, 22.368164 Banat Silver region, Romania - Argentiferous copper ores. 50.909961, 13.353882 Erzgebirge, Germany - Literally: Ore Mountains. The area with the mining towns of Freiberg, Marienberg, Annaberg, Schneeberg, Johann-Georgenstadt and Schwarzenberg (all to the southwest of this marker, extending into the Czech Republic)) have been silver producing centres since around the 11th-12th century. 51.715118, 10.523529 Andreasberg, Harz Mountains, Germany - Discovered in 1520, argentiferous galena. 44.801327, 6.556091 L'Argentière, France - Roman copper/silver mines which were in active operation in the 12th century. 47.451308, 12.397385 Kitzbühel, Switzerland - Among the deepest mines in Europe around the mid 18th century. Abandoned shortly after that date. 48.362979, -3.752861 Huelgoet, France - Argentiferous galena. 45.83478, 2.853355 Pontgibaud, France - Large quantities of galena, rich in silver. 37.996163, -5.759583 Gualcanal and Cazalla, Spain - Formerly highly productive silver mines. 41.087115, -2.999268 Hiendelaencina, Spain / Most important Spanish silver mines / discovered in 1843 by a Spaniard returning from mexico who remarked the resemblance of a rock to Mexican silver ore. Subsequent examination by a chemist indicated that it was an very rich silver ore. Guanajuato, Mexico / One of the largest silver deposits in mexico with veins of ore sometimes exceeding the 100 feet in width. 22.172145, -100.975342 San Luis Potosi, Mexico - major silver deposit. 39.337484, -119.677162 Comstock Lode, Virginia City, nevada, USA - Discovered in 1859. Extraordinary amounts of silver have been mined here, fueling the settling of the West and enabling the economy of San Francisco (the port to which the silver was hauled) to grow very fast in a very short time. 39.497815, -117.065849 Reese River Mining region, Nevada, USA - A mineral rich area which basically comprises the whole north east of Nevada. Numerous silver mines around Austin, Lander County. 68.071989, -162.876044 Red Dog Mine, Alaska - Major zinc deposits that contain silver as well. In operation since 1989. 58.401352, -134.517975 Green's creek silver mine 31.725393, -110.064983 Tombstone district, Arizona - Most productive silver mining district in Arizona. Discovered in 1877. Argentiferous copper deposits. 36.171971, -117.088509 Silver mines at Panamint in Inyo County produced silver from 1873 until the town was destroyed by a flash flood in 1876. 36.537329, -117.793822 Gerro Gordo Mines, California - Mining operations were undertaken from 1866 until 1957, producing high grade silver, lead, and zinc ore. 34.948146, -116.863289 Silver was discovered at Calico in San Bernardino County in 1881, and mining was prosecuted strongly there until 1896. 35.367566, -117.642117 Rand District, California - Silver was mined from 1919 to 1928. 39.581514, -105.870438 Silver veins were first discovered in the Montezuma district of Summit County in 1864. 39.242624, -106.28912 Leadville, Colorado - Colorado’s largest silver district, discovered in 1874. 38.725965, -105.142078 Cripple Creek & Victor mine, Colorado - The largest current source of silver in Colorado as a byproduct of gold mining 47.69405, -116.747589 Coeur d’Alene, Idaho - Among the top 3 silver districts of the world. 3 Main mines in the district, the firts of which dates back to 1887. 46.030342, -112.494507 Butte, Montana - historically the second-greatest source of silver in the United States. In 1874 prospectors discovered silver veins here. 46.328439, -113.287582 Phillipsburg, Montana - Silver was discovered here in 1864. 43.889419, -71.175098 Silver Lake Mine, Madison, NH - Silver mining from 1826 - 1918 44.412356, -71.11167 Shelburne & Mascott lead-silver mines, New Hampshire - The Shelburne mine was worked from 1830's -1850's and the mascott mine from 1881-1885. 44.05157, -71.673088 North Woodstock mine, NH - Lead-silver ores. 34.093184, -107.230682 Magdalena, NM - Silver discovered in 1863. 32.775151, -108.261337 Silver City, NM - Major silver-mining area discovered in 1876 36.08143, -108.149672 Lake Valley silver deposits, NM - discovered in 1876 35.706133, -80.200152 Silver Hill Mine, NC - Discovered in 1838. First silver mine in the US. worked until the 1870's. 31.109976, -104.991875 Allamoore-Van Horn silver mining district, Texas - discovered in 1880. Silver and Copper. 29.815867, -104.307139 Shafter, TX - Silver discovered in 1880/1881. Six mines were worked here. 40.558548, -112.131443 Bingham Canyon Mine, Utah - Largest silver producing mine in Utah. Byproduct of copper mining. 40.658243, -111.505737 Park City district - Silver discovered in 1886. More info 48.289589, -117.70752 Chewelah District, Washington - Considerable silver deposits. 31.192245, -110.995216 Planchas de Plata, Nogales, Mexico - native silver in placers discovered in 1736. 49.500465, -117.302055 Nelson, British Columbia, Canada - Silver discovered in 1886. 49.910224, -116.915474 Kaslo, British Columbia - Silver district from the late 19th century. 49.763914, -117.463331 Slocan, British columbia, Canada - massive silver strikes in 1892. 49.990912, -117.368059 New Denver, British Columbia, Canada - 1892 39.19315, -106.813545 Aspen, Colorado - Silver mining since 1879 39.981033, -105.577948 Caribou Silver District - discovered in 1861 37.938309, -107.813945 Telluride, Colorado - Gold was first discovered here in 1858. The mines of Telluride were rich in silver as well. 47.402765, -79.68137 Cobalt, Ontario, Canada - Silver was discovered in the area in the summer of 1903 -19.603054, -65.74811 Potosí, Bolivia - Established as early as 1546, it soon produced fabulous wealth, becoming one of the largest cities in the Americas and the world, with a population exceeding 200,000 people. 14.061988, -87.242432 Tegucigalpa District, Honduras - Silver Mining since Spanish settlement in the 16th century. 14.489866, -89.45137 Chiquimula District - Major silver deposits in Guatemala. -10.687599, -76.27224 Cerro de Pasco, Peru - One of Peru's most important silver mining regions. Discovered in 1630. -7.1554, -78.502121 Cajamarca District, Peru - various silver mines. -7.721878, -77.607422 Pataz, Peru - Various silver mines. -6.755988, -78.602371 Hualgayoc, Peru - Various silver mines. -28.21971, -71.054077 Mountains north of Huasco, Chili - major silver deposits in Chili. -29.501769, -71.218872 La Higuera, Chili - Rich copper mines with silver as a byproduct. -27.357742, -70.30632 Copiapó District, Chili - Most important silver mining area in Chili. 29.859701, -9.074707 Anti-Atlas Mountains, Morocco - Rich in gold and silver. -25.562265, 27.27356 Merensky Reef, South Africa - Silver is mined here as a byproduct of Platinum Group minerals. -26.246158, 28.219929 East Rand Mine, South Africa - Major gold mine with silver as a byproduct. -26.413549, 27.389603 Carletonville, South Africa - Tautona Mine. major gold mine with silver as a byproduct. -31.961484, 141.503906 Broken Hill, NSW, Australia - Silver as a byproduct of lead-zinc mining. -20.724328, 139.489975 Mount Isa, Qld, Australia - Silver as a byproduct of lead-zinc mining. -16.417315, 136.063614 McArthur Mine, NT, Australia - major lead-zinc-silver deposit. 22.595152, 86.451159 Hindustan Copper Ltd. - Silver as a byproduct of copper mining. 62.572473, 155.284882 Magadan, Russia - The countries largest silver mine. 56.067436, 92.842712 Krasnoyarsk territory, Russia - One of the main silver producing areas of the country. 54.244366, 56.170349 Bashkortostan, Russia - One of the main silver producing areas of the country. 55.168672, 61.410828 Chelyabinsk, Russia - one of the main silver producing areas of the country. 51.81286, 55.193939 Orenburg Region - One of the main silver producing areas of the country. 35.107341, 132.437932 Iwami Ginzan Silver Mine, Japan - Established in 1526, peak production around the early 17th century. 44.135037, 143.348837 Konomai Gold Mine, japan - Discovered in 1915 worked until 1973. Produced more silver (1200T) than gold (73T). 34.908264, 138.792922 Toi Gold Mines, Japan - The first gold-silver mine of Japan. Small scale workings as early as 1370. Closed in 1965. </googlemap>
Have we missed a deposit? please let us know!

Further Reading: Mining & Metallurgy


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