Natural tin–copper associations and unintentional bronze? A multiscale archaeometallurgical study from the Sierra de Fiambalá (NW Argentina)

Bronze, a copper–tin (Cu–Sn) alloy, is an early metallurgical innovation valued for its hardness, low melting point, castability, ductility, and resistance to corrosion. In Northwestern Argentina (NOA), archaeological literature has traditionally assumed intentional bronze production; however, when tin contents fall below ~2%, many Cu–Sn alloys are classified as unintentional, reflecting trace Sn in copper ores rather than deliberate alloying. This paper examines the possibility of unintentional Cu–Sn bronzes in the Sierra de Fiambalá (Catamarca, Argentina), where natural ore associations may produce bronze without explicit alloying decisions. We present geological and geochemical data from mine prospections documenting variable Cu–Sn mineral assemblages, integrated with regional economic geology, historical mining reports, and oral testimonies from former miners used to locate mineral-rich veins. These data are linked to regional archaeological evidence for ore processing, smelting, and metal manufacture, situating our analysis at the early stages of the mining–metallurgical chaîne opératoire. Our multiscale approach suggests that during the early phases of mining in the region, some Cu–Sn alloys may have arisen from natural geological variability, a “metallurgical incident” rather than purposeful alloying. This perspective reframes assumptions about technological intent and highlights how ore geology can structure metallurgical outcomes along the chaîne opératoire, from resource extraction to artifact production.