Documenting the History of Inca Precious Metal Production using Geochemical Techniques from Lake Sediments in the Andahuaylas Region of Peru

The process of studying heavy metal concentrations in lake sediments in order to reconstruct pollution history has been used in a variety of environments and locations. Laguna Pacucha is one in a series of metal pollution studies from Peru and Bolivia, an area with a rich history of metallurgy. Laguna Pacucha lies in the Andahuaylas region of Peru, 145 km west of Cuzco, the Inca capital, and 20 km west of Curamba, a presumed ancient smelting site. The sediment record of Laguna Pacucha reveals a metal record that dates beyond 1225 AD. A major density change ~1225 AD, concurrent with a known period of drought, inhibits the possibility of a reliable age model below this point. Increases in Zn, As, and Cu after ~1225 AD could be indicative of local copper smelting, which supports separate evidence of the Curamba archeological site (near Laguna Pacucha) as a potential copper smelting site. These concentrations drop around the time of the Spanish conquest, and then the concentrations of a number of different metals increase after ~1600 and decrease by ~1850 AD, which could indicate smelting, but more likely indicates a change in land use. Our results provide a complex record of a changing Andean environment, and indicate a need for further study in the Andahuaylas region