The Romans exploited the silver deposits in Portugal and Spain to make coins

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Silver became widely used for currency in the Roman world from the 7th century BCE and provided a standardized monetary system for ancient Mediterranean civilizations.

The problem is that it is difficult to determine which deposits the Roman miners mined because most of them have been depleted.

However, those that still survive in the southern region contain galena, which is the main ore of lead and an important source of silver. To track the source of the Roman silver, the team analyzed the silver and lead compositions of galena samples from some of these deposits and compared the results to the chemical signatures of Roman silver coins.

Sample of Iberian galena. (Photo by Jean Milot).

They identified two different types of galena deposits based on the elemental silver composition of the samples: silver-rich galena which would have been a probable source for Roman money, and silver-poor galena which would have been mined for the lead and would have been of lesser economic importance.

Yet few ore samples had a composition that matched the elemental silver composition of Roman silver coins. Argentiferous ores covered a wide range of compositional variability, but Roman coins notably had a very narrow elemental composition range.

Based on the elemental lead signatures of the galena samples, the ore deposits of southeastern Spain best match the makeup of Roman coins, suggesting that these deposits were a major source of silver. Roman. Both silver-rich and silver-poor galena deposits have likely been mined there, with lead mined from silver-poor galena that can be mixed with other ores to extract silver.

These results based on chemical analyzes are also consistent with archaeological evidence of ancient mining in the area.

“This work is to be extended to the silver-rich region in which the currency was invented in the 6th century BCE, Greece and Asia Minor (modern Turkey),” Milot said in a press release. “The method we describe here will allow us to recognize the lost ore deposits that provided silver to the Eastern Mediterranean empires from the Bronze Age to the collapse of the Hellenistic kingdoms.”


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