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Newsletter Blast from the Past: Early Irish Copper Mining

Originally published January 2012

The large number of copper and bronze artifacts found in the Cork-Kerry area reflects copper’s importance in Bronze Age Ireland. The metal “industry” taking advantage of readily exploited copper ore deposits is credited for an increased in settlements in this region between 2500 and 500 BC. Exposed copper outcrops appear in fairly heavy concentrations along the south Cork coastline, but we seldom think of the huge amount of labor required to produce even small amounts of metal.

Mount Gabriel is the highest mountain on the Mizen Peninsula in south-west Cork and this mass of Old Red Sandstone was the site of extensive surface mining of copper ore. Thirty-two excavations have been identified on its eastern slopes. These are among the oldest known copper mine in north-west Europe. Radio carbon dating of wood and charcoal from these sites put the primary period of activity ranging from between 1700 and 1900 BC. The sites were also well preserved by a layer of upland blanket-bog. The sites are often identified by the mounds of rock debris that accumulated outside the mine and contain a high concentration of charcoal and broken stone tools.

The mines are not terribly deep, some were mere surface operations less than 2 meter deep. The simple tools and techniques available at the time limited the workers to depth of no more than 10 to 15 meters. The mines show no evidence of the use of metal tools, but rather used a a technique used by primitive mining operations around the world. Bonfires would be set against the rock face for several hours causing it to crack or fracture. Then stone hammers or “cobbles” would be used to pound the surface to break rocks from the surface along with wooden wedges to pry loose cracked rocks from the heat-shattered surface. The rock then would be crushed with stone tools to separate the greenish copper-bearing ore from the waste rock before being transported to a location with the substantial amount of fuel needed for the smelting process. Due to the amount of fuel needed for this type of mining, scholars have assumed the work was divided between two teams: those who worked extracting and sorting the ore, and those involved in gathering fuel and the beach stones used as the cobble hammers.

One would think you would want to smelt the ore near the mine to avoid transporting the rock, but huge amounts of fuel were needed for this process. Thus, it was more economical to transport the ore from the minehead to a location with an abundant supply of wood. The -lowest- estimates for copper production in the area are about 20 kilograms (44 lbs.) per year. The concentration of copper in the ore seems to have been only an average of about 2% -requiring around one metric ton of ore to be refined each year. It is estimated that at total of 2500 metric tons of dry fuel would be required to refine that 1 metric ton of ore. But we have to remember that the fuel would need to be prepared ahead of time. The trees would have to be felled, cut, and to allowed to dry before being converted to charcoal. Estimates are that it would then take two men a week of tending the primitive furnace to complete the smelting process and produce 20 standard ingots weighing an average of about one kilogram each. Only then could the metal actually be cast into usable forms -again require two men about a week and tons of more wood to melt the metal alloy it with tin and pour it into simple, carved stone molds to form axes.

Groomporter

Blogger for The Celtic Croft and owner of MacGregor Historic Games http://historicgames.com

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