Andean Ores, Bronze Artifacts, and Lead Isotopes: Constraints on Metal Sources in Their Geological Context

Abstract

With a focus on bronze production in the south-central Andes during the Middle Horizon, this study reports the first archaeological use of lead isotope analysis to investigate metallic ores and metal artifacts in the Andean zone of South America. Because the vast majority of metal deposits in the Andean cordillera formed in a convergent plate boundary setting, lead isotope compositions of most Andean ore sources are not unique. Lead isotope ratios of central and south-central Andean ores define four geographically distinct ore lead isotope provinces, oriented and elongated parallel or sub-parallel to the trend of the Andean cordilleras. Consequently, ore lead isotope ratios vary strongly from west to east along transects through the coast, highlands and altiplano, but they exhibit much less variation from north to south. The strong west-to-east variation in ore lead isotope signatures allows discrimination between ore bodies, and ultimately between metal artifacts, as a function of macro-ecozone location: coast, junga-qiswa, puna, altiplano. We present the most up-to-date database of ore lead isotope signatures for the south-central Andes including those determined for ores we sampled over an approximate 250,000 km sq region within Bolivia, N. Chile, and NW Argentina. Lead isotope signatures of Cu-As-Ni bronze artifacts from Tiwanaku (altiplano capital) and San Pedro de Atacama (desert oasis entrepôt) establish that altiplano and high sierra ore bodies provided the metal for both assemblages. Conchopata (Wari) arsenic bronze artifacts exhibit lead isotope ratios compatible with the Julcani (Huancavelica) copper sulfarsenide deposit.

Producción Metalúrgica Local Y Coexistencia De Tecnologías Metalúrgicas en San Pedro De Atacama Durante El Período Medio (400-1000 Dc)

“…El estudio también evaluó el origen geoquímico de 16 hachas a través de isótopos de plomo, determinándose que habrían sido elaboradas a partir de menas altiplánicas, descartando a SPA como proveedor de las materias primas o productor de tales artefactos, aunque podrían haber sido manufacturadas en la aleación Cu-As-Ni proporcionada por Tiwanaku. Tres hachas podrían provenir desde menas cupríferas próximas a los oasis de SPA (Macfarlane y Lechtman 2015), las cuales desgraciadamente no sabemos si corresponden o no a los objetos elaborados en cobre no aleado.…”

“…La aleación Cu-As-Ni corresponde a la firma altiplánica por excelencia, particularmente porque se encuentra espacial y temporalmente circunscrita a la región altiplánica durante el PM (Macfarlane y Lechtman 2015). Se hace presente desde el siglo II en el área de influencia Tiwanaku, siendo característica de los metales más tempranos distribuidos por esta órbita.…”

“…Recientes investigaciones, orientadas a la comprensión de la interacción interregional con Tiwanaku, se han focalizado en el análisis composicional de metales (Lechtman y Macfarlane 2005Macfarlane y Lechtman 2015;Maldonado et al 2010Maldonado et al , 2013Plaza 2015;Salazar et al 2011). Sus resultados han sido coincidentes al desestimar que la metalurgia atacameña sea de carácter local, puesto que en su mayoría se trataría de metales foráneos debido a la presencia de aleaciones no disponibles en la región y/o firmas isotópicas características de materias primas provenientes del Altiplano Boliviano o Noroeste Argentino (en adelante NOA) (Lechtman y Macfarlane 2005Macfarlane y Lechtman 2015). No obstante, junto con estos resultados existe un porcentaje de objetos elaborados en cobres no aleados.…”

Application of Kernel Density Estimates to Lead Isotope Compositions of Bronzes from Ningxia, North‐West China

“…Once these ores are smelted and cast into metal objects, variations in the resulting lead isotope ratios provide an opportunity for differentiating one metal supply from another. One comparative example is that provided by Macfarlane and Lechtman () in regard to the provenance of prehistoric Andean bronze metallurgy. Variations in local geological contexts allowed them to delineate several strongly discriminated lead isotope provinces in a west–east direction from the coastlines of Peru and Chile to the Andean Mountains.…”

Investigation of the Lead Isotope Signatures of Marine Sediments in Relation to the Lead Isotope Signatures of Northern Andean Ores

“…The area is composed of coastal and volcanic arc sediment deposited on to a basement of Mesozoic and Paleozoic sedimentary and metamorphic rock . Province I lead has been found ) which corresponds to the known isotopic composition of orogenic lead (Zartman andDoe 1981 andLechtman 2014). and Gunnesch et al (1990) teams determined that the isotopic signatures found in the rocks of Province I derived from mixing of crustal rock melt and the magmatic source.…”