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Documented the economic activity? No, they documented deposits of particles that are claimed to be from the Roman Republic smelters and also which are only the particles that existing weather patterns happened to have lead to being deposited. Talk about derivative. Not even to mention that there is little that would imply that smelting for coin production would implicitly relate to economic activity. Run away inflation or corrupt rulers do not necessarily correlate to economic activity but could very well result in increased smelting just as well as technological advances that require more smelting or buildup of the military could.