The Rio Tinto ore body is a massive sulfide deposit in the south of the Iberian peninsula. It takes its name from the nearby Rio Tinto, literally “red river,” whose colour is due to oxidation of iron contaminants leached from minerals in the nearby ore body, or from the slag heaps that dot the region. In 1873, a group of investors took over the mine, forming the Rio Tinto Group, which has since become one of the largest mining concerns in the world. However, the exploitation of the region’s mineral wealth started long before the 19th century.
Fig. 1. The Rio Tinto river, showing the deep red colour caused by the high concentration of ferric iron.
Mining activity at Rio Tinto began as early as 3000 B.C.E., when the southern Spain was occupied by the Iberian and Tartessan people. It is probably no coincidence that the Phoenicians, an eastern Mediterranean trading civilization that flourished between 1500-500 B.C.E, established their first Spanish colony at Gadir (Cadiz), which is today just a 3 hour drive from the mines at Rio Tinto. Later, the mines would come under the direct control of Carthage, a Phoenician successor state.
Following the defeat of North African state of Carthage by Rome in the Second Punic War, the entirety of the Iberian peninsula passed into Roman hands, and with it the mines at Rio Tinto. The exploitation of their mineral wealth continued apace under Roman rule, and lead isotope data suggests that Rio Tinto was the primary source of silver for Roman coinage during the early Imperial period (Butcher and Ponting, 2005).
Fig. 2. Fraction of anthropogenic lead in the Greenland ice derived from Rio Tinto and other Roman mines in the Southern Iberian Peninsula. From Rosman et al., 1997.
The smelting process used to extract silver metal from the jarosite ore mined at Rio Tinto resulted in the emission of heavy metal pollutants into the atmosphere, where they were dispersed around the world. The scale of the Roman mining operations in southern Spain may be seen from lead isotope ratios measured in the Greenland ice, where nearly 70% of the anthropogenic (ie. human-derived) lead deposited between 400 B.C.E and 50 C.E. came from the Rio Tinto ore body or its immediate vicinity (Rosman et al., 1997).
While mining activity at Rio Tinto declined in the 2nd century C.E., and again following the fall of the Western Roman Empire in the 5th century, it never completely vanished. In fact, mining continues at Rio Tinto today, with the recent expansion of a copper mine owned by Atalaya PLC, making it the oldest continuously mined formation in the world.