4,500-year-old mining pollution in southwestern Spain: Long-term implications for modern mining pollution

The Tinto river drains the Rio Tinto mining district, which comprises the w orld's largest known massive sulfide deposits; these orebodies have been mi ned from the third millenium BC to the present. The Tinto river is strongly acidic (pH, 1.5-2.5); during flood events, it transports a sandy material, including abundant detrital pyrite grains. A core drilled in the Holocene sediments of the Tinto estuary allows for investigation of recent and histo rical mining pollution. Two anomalous horizons have been recognized (0-1.3 m; 3-4 m). Both are characterized by very high metal content (100 times ove r the background) and by the presence of abundant elastic pyrite grains. Th e metal association (Pb, Ba, As, Cu, Zn, Sn, Tl, Cd, Ag, Hg, Au) is typical of that of the Rio Tinto pyritic ore. The upper horizon corresponds to the modern mining activity; the lower horizon has been dated at 2530 BC (C-14 AMS calibrated age). We show here that active mining occurred early (Copper Age) in the Rio Tint o area, resulting in a watershed-scale metal contamination. We also show th at anthropogenic input of metals may be accumulated and immobilized during thousands of years in estuarine sediments.