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The Silver Mines of Lavrion

History

Silver from the silver mines of Lavrio (or Lavrion or Laurion) was the source of wealth and power of ancient Athens.

The playwright Aeschylus called Lavrion the "treasure house of the country".

General Themistocles used the silver to build a wall around the city of Athens (which extended down to Piraeus) to keep out the Spartans. He also used it to build a fleet of about 310 ships (Triremes) which were used to defeat the Persian fleet of 500-600 warships at the battle of the island of Salamis in 480 BC. With the defeat of the Persians, the Greeks entered their "Golden Age" (461-431 BC) which changed the course of history.

Later, the Athenians finally lost the Peloponnesian wars against the Spartans because the Spartans, instead of returning home for the winter months, camped between Athens and Lavrio and blocked the supply of silver to the city - thus causing a chronic shortage of money in Athens.

The silver-bearing ores had been exploited since the Bronze Age. In 482 BC the discovery of an especially rich silver vein led to a massive increase in mining activity. At it's peak, 350 mines produced 1000 talents (1 Greek talent = 82.5 lbs. or 37.5 kilos) of silver a year worked by 10-20,000 slaves. The 'industrial slaves' were prisoners of war & mostly barbarians who were purchased for a low price. Their life expectancy was short and they worked in conditions of indescribable squalor. The mines were worked 24 hours a day, 7 days a week and from the discovery of miners lamps containing oil, the slave's shifts have been estimated at 10 hours straight. The slaves had no vacations!

The city-state of Athens maintained strict control over the purity of the silver produced in Lavrio and minted the famous "owls" silver coins designed for wide circulation. Because of the purity, the coins were accepted far and wide and gave the ancient Athenians much 'buying power'.

Tetradrachm c. 450-440 B.C . Note: The vertical Alpha Theta Epsilon - abbreviation for Athens.

In total, the mines were exploited for their silver-bearing ores for 25 centuries. Over 2000 mines have been recorded in the hills around Lavrio. The main ancient mining activities took place in an area known as Agrileza - not far from the village of Kamariza (also called Ag. Konstandinos). The ancient workshops in Souriza's Valley and round the base of Michalis Mountain are now protected within the Sounio National Park.

The silver extraction process

The ore used to extract silver was not a silver ore but Lead Sulphide (formula PbS), known as Galena or Galenite (named by the Roman Pliny) which contains 87% lead. The local variety of Galenite is silver-bearing and is known as Argentiferous Galenite (formula (Pb.Ag)S ) and the lead obtained from this ore contains just a small percentage of silver - from 0.8% up to 5%.

The ore as mined was not pure as it was encased in rock, combined with earth, and also contained traces of iron ore and other minerals. Firstly it had to be pounded into small fragments on stone tables with rock hammers, then ground to a fine powder of 1-mm grain size in a stone mill (very hard work!). Then it had to be washed in a "washery" to remove as many of the impurities as possible. The washed ore was then dried and formed into bricks.

Next, the bricks of washed ore were heated in a furnace where the lead/silver mixture was released from it's sulphide and separated from iron oxide impurities and run-off into "pigs" or blocks.

The pigs of lead were now placed in a high temperature (950 degC) 'Cupellation' furnace with materials capable of oxidising (absorbing) the lead. The lead oxide was scraped out of the mixture using iron bars. The silver that remained was run-off and solidified into blocks.

Since lead was also valuable, it was recovered by placing the lead oxide remaining from the cupellation process into yet a third furnace and heated to 250 degC and air was blown through it. The lead was run-off and formed into rods.

Since lead is a cumulative poison, many slaves must have died from its effects; not to mention from the sulphur dioxide fumes from the original lead sulphide processing furnaces.

The Cisterns and Ore Washeries [These you will see in Souriza's Valley - built about 500 B.C.]

Water was vital to the ore washing process but it was in short supply up in the hot, dry hills around the Kamariza area. So it had to be collected and conserved and recycled to allow a year-round operation. This determined the design of the cisterns and washeries.

The cisterns were build to collect and store water during the rainy months, but the water had to be clean for the ore washing process. The water running down from the hillsides to the cisterns would have been muddy and dirty. So each cistern system had a smaller sedimentation or settlement tank next to it to receive the muddy water and clarify it before feeding it to the large main tank. Re-cycled water from the ore washeries would also be tipped into this settlement tank. The cisterns had to have an excellent waterproof lining to prevent leakage. The cement for the lining was believed to have been brought from Santorini - where it was made from the volcanic rock.

The ore washeries were designed to conserve and recycle water. A water tank at the rear of the washery was filled by bucket (slaves) from the main cistern. The water from the tank was tipped down moveable open pipes containing the unwashed ore. The lead ore was heavy, so the impurities, which were lighter (or soluble in water), ran off into a channel where the water then ran into settlement tanks. The washed ore could then be placed on the open area of the washery where it drained and the water collected by the surrounding channel system. So no water was lost and after the solids had settled out in the system of sedimentation tanks, the precious water was transferred by bucket back to the cisterns for re-use. The sediment would have to be periodically cleared from these tanks as they filled-up.

MD - Oct. 2003

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