The Production of Copper-arsenic Alloys in the Central Andes: Highland Ores and Coastal Smelters?

Abstract

The alloy of copper and arsenic was one of the most common metallurgical products in the central Andean area during the Late Intermediate Period (A.C. 900–1476), and a large part of that production took place at smelting sites on the north coast of what is today Peru. The research of the Battán Grande-La Leche Archaeological Project has made available for the first time a rich body of data on the smelting/refining furnaces used to win copper-arsenic metal from metallic ores at Battán Grande, a key north coast center of production of the alloy. There is general agreement that mixed ores were charged into the Battán Grande furnaces, some containing minerals that contributed primarily copper to the alloy, others that contributed primarily arsenic. Whereas the types of copper ore have been identified, the types of arsenic-bearing ores and their sources remain in question.The two arsenic minerals most likely to have been used in the north coast production of copper-arsenic alloys are enargite and arsenopyrite; the former is a mineral found only in the high sierra of the central Andes, whereas the latter is also available in some of the north coast valleys. No specimens of enargite have been reported thus far at Battán Grande, but this article discusses the identification of one example of enargite ore from the nearby metallurgical site of Batanes del Tablazo, in the Chancay Valley. Inferences drawn from a single ore specimen must be made with caution, but the new data lend support to the argument that one of the main sources of supply of arsenic-bearing ores for coastal smelters was the deposits located in the highlands to the east. The mechanisms by which these ores may have been brought to the coast remain a matter of conjecture.