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Lead mining

Lead was essential to the smooth running of the Roman Empire. It was used for piping for aqueducts and plumbing, pewter, coffins, and gutters for villas, as well as a source of the silver that sometimes occurred in the same mineral deposits. Fifty-two sheets of Mendip lead still line the great bath at Bath which is a few miles from Charterhouse (see below).

The largest Roman lead mines were located in or near the Rio Tinto (river) in southern Hispania. In Britannia the largest sources were at Mendip, South West England and especially at Charterhouse. In A.D. 49, six years after the invasion and conquest of Britain, the Romans had the lead mines of Mendip and those of Derbyshire, Shropshire, Yorkshire and Wales running at full shift. By A.D.70, Britain had surpassed Hispania as the leading lead-producing province. The Spanish soon lodged a complaint with the Emperor Vespasian, who in turn put limits on the amount of lead being produced in Britain. However British lead production continued to increase and ingots (or pigs) of lead have been found datable to the late second - early third century. Research has found that British lead (i.e. Somerset lead) was used in Pompeii - the town destroyed in the eruption of Vesuvius in A.D.79.

Roman lead mined from Mendips, Derbyshire, Durnham and Northumberland were mainly sourced for its lead content. The silver content of ores from this country was significantly lower than Athenian lead-silver mines and Asia Minor mines.

Smelting is used to convert lead into its purest form. The extraction of lead occurs in a double decomposition reaction as the components of galena are decomposed to create lead. THe reducing agent in this reaction is the sulfide and fuel is only needed for high temperature maintenance. Lead must first be converted to its oxide form by roasting below 800C using domestic fire, charcoal or dry wood. This is done easily as lead melts at 327C. Lead oxide (PbO) is the oxide form of galena which reacts with the unroasted form lead sulfide (PbS) to form lead (Pb) and sulfur dioxide (SO2).

Details on Roman lead smelting has not been published although open hearths were found in Mendips by Rahtz and Boon. These remains contained smelted and unsmelted ores. The remains of first century smelting was found in Pentre, Ffwrndan. Althoug this discovery was valuable, reconstruction of the remains were impossible due to damage. An extracted ore from the site had a lead content of 3 oz. 5 dwt. per ton and another piece contained 9 oz. 16 dwt per ton of lead.

Silver extraction

The most important use of lead was the extraction of silver. Lead and silver were often found together in the form of galena, an abundant lead ore. Galena is mined in the form of cubes and concentrated by removing the ore-bearing rocks. It is often recognized by its high density and dark colour. The Roman economy was based on silver, as the majority of higher value coins were minted from the precious metal. British ores found in Laurion, Greece had a low silver content compared to the ores mined from other locations. The Romans used the term Britain silver for these lead mines.

The process of extraction, cupellation, was fairly simple. First, the ore was smelted until the lead, which contained the silver, separated from the rock. The lead was removed, and further heated up to 1100° Celsius using hand bellows. At this point, the silver was separated from the lead (the lead, in the form of litharge, was either blown off the molten surface or absorbed into bone ash crucibles; the litharge was re-smelted to recover the lead), and was put into moulds which, when cooled, would form ingots that were to be sent all over the Roman Empire for minting.Silchester, Wroxeter and Hengisbury Head were a known location for Roman cupellation remains.

When inflation took hold in the third century A.D. and official coins began to be minted made of bronze with a silver wash, two counterfeit mints appeared in Somerset - one on the Polden Hills just south of the Mendips, and the other at Whitchurch, Bristol to the north. These mints, using Mendip silver, produced coins which were superior in silver content to those issued by the official Empire mints. Samples of these coins and of their moulds can be seen in the Museum of Somerset in Taunton Castle.

Gold mining

Development of Dolaucothi Gold Mines

The aqueducts at Dolaucothi

The native form of silver is gold, which can be mined in Linlithgow in Scotland, Cornwall and other British Isles locations. Melting was necessary for this form of native silver as it is found in a form of leaves or filaments.

Britain's gold mines were located in Wales at Dolaucothi. The Romans discovered the Dolaucothi vein soon after their invasion, and they used hydraulic mining methods to prospect the hillsides before discovering rich veins of gold-bearing quartzite. The remains of several aqueducts and water tanks above the mine are still visible today. The tanks were used to hold water for hushing during prospecting for veins, and involved releasing a wave of water to scour the ground and remove overburden, and expose the bedrock. If a vein was found, then it would be attacked using fire-setting, a method which involved building a fire against the rock. When the hot rock was quenched with water, it could be broken up easily, and the barren debris swept away using another wave of water. The technique produced numerous opencasts which are still visible in the hills above Pumsaint or Luentinum today. A fort, settlement and bath-house were set up nearby in the Cothi Valley. The methods were probably used elsewhere for lead and tin mining, and indeed, were used widely before explosives made them redundant. Hydraulic mining is however, still used for the extraction of alluvial tin.

Long drainage adits were dug into one of the hills at Dolaucothi, after opencast mining methods were no longer effective. Once the ore was removed, it would be crushed by heavy hammers, probably automated by a water wheel until reduced to a fine dust. Then, the dust would be washed in a stream of water where the rocks and other debris would be removed, the gold dust and flakes collected, and smelted into ingots. The ingots would be sent all across the Roman world, where they would be minted or put into vaults.