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Copper ore sources exploited during the Late Postclassic Period (1300 to 1521 A.D.) were located by means of lead isotope analyses of copper ores from 15 deposits in West Mexico, Oaxaca, and Veracruz and of 171 copper artifacts from nine Mesoamerican archaeological sites in West Mexico and in southern, central, and northeastern Mesoamerica. West Mexican ores provided copper metal for most artifacts from the west Mexican settlements of Atoyac and Urichu, as well as for some artifacts from Aztec towns, Huastec centers, a Maya site, and settlements in Oaxaca and Chiapas. West Mexico was not marginal to Mesoamerican events but played the primary role in the production and distribution of copper and bronze artifacts, one of Mesoamerica's key exotic goods.
Metal artifacts first appeared in Mesoamerica in the west around 650 A.D. Metallurgy was introduced from South America by a maritime route. West Mexico contains the most varied array of ore minerals available to ancient Mesoamerican smiths, including copper carbonates and sulfides, arsenopyrite, argentite, and silver sulfosalts. Cassiterite, the tin oxide ore, occurs in a southwestern extension of Mexico's Zacatecas tin province. West Mexican metalworkers focused primarily on fashioning ritual and sacred objects throughout the 900-year history of this technology. Before 1200 A.D., they used copper, principally for bells but also for small cold-worked implements. After 1200 to 1300 A.D., they produced copper-arsenic bronze, copper-tin bronze, and copper-silver alloys, not only for their golden and silvery colors but also to optimize the design and functionality of objects previously made in copper. Bells and elaborate tweezers as well as needles, awls, and other tools from this time appear at other Mesoamerican sites (1-4). Here, we present lead isotope data that demonstrate that many of these artifacts were produced in the west Mexican region.
Geochemical and Archaeological Context
Lead isotope (LI) analyses can be used to identify ore sources for artifacts made from copper and copper alloys (5) by matching the isotopic signatures of ore lead to those of the artifacts. The isotopic composition of ore lead is a function of the age and chemistry of the source rocks. Lead is present at analyzable concentrations in all copper artifacts. Because LI compositions are not altered during ore smelting, they provide a means of identifying the ore...