Mines of Laurion

The mines of Laurion are situated in the Attic-Cycladic metamorphic complex. Structurally, the Laurion area bedrock consists of a recumbent fold in the Kamariza marble with the Kamariza schist forming a hinge. Atop the folded marbles lie a layer of limestone deposited during a marine transgressive episode in the Jurassic and lower Cretaceous. This limestone layer is topped by Jurassic blueschists and overthrust, metamorphosed ophiolite.[10]

Diagram showing Laurion area strata with contacts I, II, and III labeled

Miners in the 19th century organized the major deposits in this sequence into three separate contacts. The first contact is located within the transgressive limestones and consists of lead, zinc and silver sulfide minerals. The second contact occurs between the upper Kamariza marble and the Kamariza schist. This deposit consists of cerussite (lead carbonate) and smithsonite (zinc carbonate) ores. The third contact occurs between the lower Kamariza marble and Kamariza schist. This deposit contains cerussite and iron oxides.[10]

This is a photograph of a mining shaft located in Thorikos which is home to several mining spots in the greater Laurion mining region.

A rectangular washery at a washing site of the mines of Laurion located in Thorikos.

For almost 300 years the mines of Laurion provided ancient Athens and their allies with several thousand tons of high purity silver.[5] However, this much silver did not come from one particular mining spot. Around 700 ancient mine shafts have been discovered along with about 200 ore processing stations.[11] At these sites, the silver ore was first extracted from the mine shafts and brought to the surface with containers by workers who were most likely slaves. It has been estimated that almost 20,000 slaves worked the mines and fulfilled various tasks from extracting the ore to washing it in the washing stations.[5] Throughout the mining region of Laurion, there were a few different versions of washing stations where the silver ore was processed.[12] All of these workshops had three basic elements. Each possessed a large cistern to store large amounts of water that were situated next to the ore washery and nearby were the living quarters of those who worked the site.[13] The water from this cistern was typically fed into a few different nozzles that lead to the sluices, which were wooden troughs meant to filter out large ore pieces that might still need to be ground into smaller sizes.[12][13] When the ore slurry was acceptable it flowed through a series of stone or cement channels that flowed in a rectangular shape.[13] However, not all washeries were rectangular in shape. According to research conducted by Professor C. E. Conophagos, a professor of metallurgy at the Polytechnic or National Technical University of Athens, other mining sights that used circular or helicoidal ore washeries were more efficient but also more rare.[12] Only a few round washeries have been discovered at the Bertseco and Demoliaki sites.[12] As the slurry flowed through these washery channels there were various settling "tanks" where the heavier more "pure" silver ore would fall to the bottom.[12][13] The impure particles kept flowing and would be later disposed of. Afterward, the pure particulate would be collected and transported to the smelting sites where ancient industrial furnaces smelted the silver ore using various metallurgic cupellation methods.[12] The "pure" silver ore actually contains an excessive amount of lead that still needs to be removed.[14] This ore is heated to very high temperatures in order to separate the lead from the silver which each display different physical properties when subjected to intense heat.[14] Once the various smelting processes are complete the silver is ready to be fashioned into various objects such as coins.[14]

There are two very prominent mining sites of Laurion that archeologists have been able to analyze and understand. The first is Thorikos which is located in the northern part of the Laurion mining region near Francolimani Bay.[12] The second site is Soureza which is situated in the southern portion of the Laurion mining site near Mt Michaeli.[12] A study conducted by Ghent University performed hydrological analysis throughout the Laurion mining region in order to reconsider the role of Thorikos in the mines of Laurion.[13] Since water is essential in processing the silver ore a continuous water supply was a necessary component to how these washing workshops functioned.[13] Researchers used hydrological modeling to simulate the water supply that the ancient washeries were operating on.[13] The study found that the Soureza workshops sourced their water supply from ephemeral streams where the streams were tapped and used to feed large cisterns.[13] At Thorikos the cisterns were fed by the collecting of runoff from the scarce rainfall which failed to provide a sufficient amount of long lasting water.[13] As a result of this poor water supply the study had to conclude that Thorikos was a widely less productive site when compared to the Soureza washeries.[13]

The mines of Laurion were an important source of metal during Ancient Greece and helped to fabricate many of the coins that were exchanged as money throughout the region.[15] Within the mines, located on the southeast portion of Attica, there are large silver deposits that also contain an abundance of copper and lead.[16] It is important to note that although the mines contained some of the highest silver deposits in Attica, the percentage of silver in the extracted ore is only 0.1%.[15] The metal ore of the mines contain a specific isotopic ratio of lead within the silver, that is later turned into coins by the Greeks.[16] Lead isotopic analysis can differentiate the origins of a particular metal structure from that of another.[17] Although this does not mean that the origin of these coins can be definitively determined, it does mean that a set of two particular coins do or do not possess a common origin.[17] Other mines in the Mediterranean, such as those on the islands of Siphnos and Thasos mentioned by Herodotus, have similar lead ratios but differ enough for archeologists and physicists to pinpoint where the silver originates.[16] This has been demonstrated by the Analytical Chemistry Division at the Institute for Materials Research National Bureau of Standards, located in Washington, D. C. Where a group of archeological chemists have used precise mass spectroscopy to determine the lead isotopic ratio of the silver ore located in the Laurion mines.[17] This same analytical process was applied to the samples of smelted silver in the form of Ancient Greek coins from the classical period of Greece in Ancient Athens and surrounding cities.[16] This showed that the Athenians minted their silver coins almost exclusively at the Laurion mines whereas the surrounding cities obtained their silver ore from where ever they could.[16] These Athenian coins were highly sought after because of their origin in the Laurion Mines. The level of mineral purity within the extracted ore was incredibly rare throughout the ancient Greek world and Athens had exclusive access to it.[18] Athens would then use their access to the Laurion mines to direct a majority of the silver to be made into coins that would be used to pay for the famous Athenian navy.[18] This silver paid for the navy that would later award Athens victory over the Persians and would later given them influence over most of Greece.[18] However, the mine's influence over Greece began to fade as its silver deposits ran dry sometime between 400-300 BCE.[19]

After the Peloponnesian Wars at around 400 BCE, Athens was in decline and the mines of Laurion had been spent on almost all their silver.[20] Since the flow of silver from the mines wained, the Athenians began to re-mint their coins by the masses in to keep the economic growth they were receiving alive.[21] They are a few notable accounts of the economic impact of this practice. The Athenian leader Hippias had tried this practice a century before by imposing very specific coinage policies that Oeconomica wrote about:

“he also made the coinage existing among the Athenians legally invalid (adokimon), and, having fixed a price, ordered them to bring it to him; and after they had come together for the purpose of striking another type (character), he gave back the same silver money (argurion)."[21]

Hippias's goals were not clear but Oeconomica highlights that his actions had disturbing economic effects. The Athenian leader was able to make a decent profit from the devaluation of all the coins in the city.[21] He required that the current devalued coins be exchanged for "legal coins" that were given a higher value.[21] After the Peloponnesian wars had ended and the mines had run dry this devaluation and re-minting of Athenian coins was brought to an extreme all over Attica. The ruler known as Dionysios I of Syracuse ruled from 405-367 BCE ordered that all the coinage be collected and re-minted at double its original value.[21] If citizens refused to do so they were threatened with death sentences.[21] Another ruler known as Leukon I of the Cimmerian Bosphoros who ruled from 389–348 BCE imposed almost the same thing but did not threaten the punishment of death.[21] Instead, he decreed that all coins that remain the same will be essentially worthless.[21] As leaders across Attica devalued their silver, the Laurion mines became active again around 370 BCE when some businessmen decided to rent out some of these recently abandoned mines.[22] They were more successful than expected resulting in a small economic boom in the greater Laurion region in 340 BCE.[22] However, the mines were outcompeted by the rising gold and silver industries in Macedonia and Thrace.[22] Silver prices plummeted when Alexander the Great finally obtained the Persian silver industry.[22] However, the Romans defeated the Macedonians in 168 BCE and later ordered the shut down of all of their mines to prevent Macedonia from rising again. This opened up an economic opportunity for Athens to seize. The Romans provided cheap slave labor and new technologies gave the Greeks new means of extracting silver in more efficient ways.[22] The Laurion mines were revived for a short while but they would never become the silver river they had used to be.

• Economy of ancient Greece
• Slavery in Ancient Greece
• Silver mining
• Ancient Coins
• Cupellation
• Ancient Greece
• Macedonia