65 BOLETÍN DEL MUSEO CHILENO DE ARTE PRECOLOMBINO Vol. 15, N° 2, 2010, pp. 65-87, Santiago de Chile ISSN 0716-1530 LATE PRE-HISPANIC AND EARLY COLONIAL SILVER PRODUCTION IN THE QUEBRADA DE TARAPACÁ, NORTHERN CHILE LA PRODUCCIÓN DE PLATA EN LOS PERÍODOS PREHISPÁNICO TARDÍO Y COLONIAL TEMPRANO EN LA QUEBRADA DE TARAPACÁ, NORTE DE CHILE COLLEEN M. ZORI * & PETER TRO pp ER ** INTRODUCTION Drawing on a survey of the Quebrada de Tarapacá in northern The predominant model of Inka expansion into north- Chile and excavations at the Inka and Colonial administrative ern Chile centers on their desire to gain access to the site of Tarapacá Viejo, we present archaeological evidence of small-scale purification of silver using lead. We argue that the abundant copper deposits of the region (Niemeyer use of techniques to refine silver-bearing ores most likely began & Schiappacasse 1988; Castro 1992; Lynch & Núñez in the Late Horizon (AD 1450-1532), when local metallurgists 1994; Cornejo 1995; Núñez, L. 1999; Uribe 1999-2000; may have processed minerals from the nearby silver mines Uribe & Carrasco 1999; Salazar 2002, 2008; Adán & of Huantajaya as part of their labor tribute to the Inka state. Although the adoption of mercury amalgamation technologies Uribe 2005). Curiously, less attention has been given introduced by Europeans allowed for large-scale refining of to the extraction of silver in the late pre-Hispanic silver, lead purification techniques continued in use into the period, despite ethnohistoric accounts that the mines of early Colonial Period (AD 1532-1700). Huantajaya surpassed those of Porco in their richness Key words: Inka, metallurgy, Huantajaya, silver, lead cupellation and were an important center for Inka silver extrac- tion (Cobo 1979 [1653]; Pizarro 1986 [1571]). Colonial Usando datos de una prospección en la Quebrada de Tarapacá sources further relate that much of the wealth of Lucas del norte de Chile y excavaciones en el sitio administrativo inka y Martínez Vegazo, the first encomendero of the Tarapacá colonial de Tarapacá Viejo, presentamos evidencia arqueológica de la purificación de plata en pequeña escala usando plomo. region, derived from the silver mines of Huantajaya Sugerimos que el uso de técnicas para refinar los minerales (Villalobos 1979; Trelles 1982; Núñez, P. 1984; Gavira de plata se inició más probablemente en el Horizonte Tardío 2005; Hidalgo 2009). (1450-1532 DC), cuando los metalurgistas locales pudieron haber Although documentary sources suggest that early procesado plata de las minas de Huantajaya como parte de su tributo al estado Inka. Si bien la adopción de las tecnologías prospecting at Huantajaya focused on large and easily de amalgamación de mercurio introducidas por los europeos exploited lodes of native silver, the mines also contain permitió la refinación en gran escala de los minerales de plata, veins of silver-bearing ores that would have required el uso de técnicas de purificación con plomo continuó en el additional processing, including argentite (Ag S, a silver Período Colonial Temprano (1532-1700 DC). 2 Palabras clave: Inka, metalurgia, Huantajaya, plata, sulfide), chlorargyrite (AgCl, a silver chloride) and prous- copelación con plomo tite (Ag3AsS3, silver arsenic sulfide; Brown & Craig 1994; * Colleen Zori, Department of Anthropology, University of California, Los Angeles (UCLA), 375 Portola Plaza, 341 Haines Hall, Box 951553, Los Angeles, CA 90095-1553, USA, email: [email protected] ** Peter Tropper, Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, A-6020 Innsbruck, Austria, email: [email protected] Recibido: febrero de 2010. Aceptado: octubre de 2010. 66 Boletín del Museo Chileno de Arte Precolombino, Vol. 15, N° 2, 2010 Maksaev et al. 2007). Due to the chronic lack of water, THE PRODUCTION OF SILVER VIA LEAD fuel, and food at the mines themselves, on-site refining CUPELLATION of silver-bearing ores would have been a challenge for both Late Horizon and Colonial miners. Sources from Although veins and bonanza deposits of native silver the late Colonial Period indicate that at least a portion occur in the Andes, most silver exists in polymetallic ore of the silver ores were refined in the nearby transverse deposits combined with other metals such as gold and valleys and at the oasis of Pica, where water, trees for fuel, copper (Lechtman 1976). Obtaining silver from these and agricultural resources were more plentiful (Bollaert ores would have required additional processing, one 1851; Brown & Craig 1994; Gavira 2005; Mukerjee 2008; form of which involves the use of lead. Hidalgo 2009). At the smelting stage, ancient metallurgists used We present an analysis of archaeometallurgical lead to add bulk to the metal fraction, thereby facilitat- materials characteristic of the small-scale processing ing the separation of the silver metal from the slag and of silver from the Quebrada de Tarapacá, located ap- its formation as lead-silver bullion by the end of the proximately 60 km northeast of the Huantajaya mines smelt (Howe & Petersen 1994; Schultze et al. 2009). (figs. 1 and 2). The artifacts were recovered from sev- Lead could be added to the furnace in the form of lead eral smelting sites identified in a pedestrian survey of ore, lead metal (Pb), litharge (PbO or lead oxide), or 2 18 km of the lower Quebrada de Tarapacá and from lead-containing slag (Howe & Petersen 1994; Gordon excavations at the site of Tarapacá Viejo (fig. 3). This & Knopf 2007). The resulting lead-silver bullion may multi-occupational settlement served as the administra- also contain matte, which is a mixture of metal sulfides tive center of the lower portion of the valley in both with minor amounts of silicates and traces of other base the Late Horizon and Colonial Period until the site’s metals from the original ores. abandonment in AD 1717 (Núñez, L. 1979; Núñez, P. Purification of lead-silver bullion takes place in 1984; Uribe et al. 2007; Zori 2011). Although it has not several different stages–including an intermediate pro- been possible to conclusively distinguish between late cess known as scorification–that typically culminate in pre-Hispanic and early Colonial silver refining, we argue cupellation. In scorification, the lead-silver bullion is that the techniques used to purify silver-bearing ores heated in an open ceramic vessel or on a flat ceramic were most likely introduced during the Late Horizon surface in an oxygen-rich environment. Through reac- and used to process ores from Huantajaya for the Inka tions with quartz found in the clay of the ceramic vessel state. These techniques were then used into the historic and/or other silicate minerals left over from the gangue, period, even after the adoption of mercury amalgama- a portion of the lead oxidizes and forms lead silicate tion technologies that allowed for large-scale refining slag (Schultze et al. 2009). Other base metals present of silver ores. in the original minerals are trapped in the lead silicate We first outline the process of extracting silver using slag as well, further purifying the lead-silver mixture. lead cupellation, and then discuss both ethnohistoric Scorification also results in the separation and removal and archaeological evidence for the use of lead in the of matte from the bullion. Purification in this manner purification of silver in the Andes before the arrival thus eliminates a portion of the lead as well as some of of Europeans in the sixteenth century. We explore the the other impurities from the bullion, leaving the metal historical connections between the mines of Huantajaya enriched in silver and ready for cupellation and the Quebrada de Tarapacá, where several different In cupellation, the silver-enriched bullion is heated forms of silver refining have been documented for the to a temperature of 900˚C or higher in an oxidizing en- later Colonial Period, and then provide archaeological vironment, causing the formation of litharge. Cupellation evidence that silver purification using lead occurred sometimes takes place in a hearth lined with bone ash in the Late Horizon and early Colonial Period. We or other calcareous material that absorbs the litharge suggest that some of the silver may have derived from as it forms, eventually leaving behind an unoxidized Huantajaya, and further argue that the Inka claimed button of pure silver (Tylecote 1964). Litharge also this metal as tribute. We likewise conclude that a cen- collects oxides of any base metals still present in the tral objective of the Inka state in the region was silver lead-silver bullion. Cupellation can also be carried out in extraction, along with that of copper and possibly an open ceramic vessel, or cupel. If unlined with bone other minerals. ash or other absorbent material, the silica in the clay of the ceramic vessel vitrifies when heated, blocking the absorption of the liquid metal oxides (Söderberg 2004). Because litharge is immiscible with the silver metal, Silver production in the Quebrada de Tarapacá / C. Zori & P. Tropper 67 Figure 1. Sites mentioned in the text. Figura 1. Sitios mencionados en el texto. 68 Boletín del Museo Chileno de Arte Precolombino, Vol. 15, N° 2, 2010 Figure 2. Tarapacá Region of northern Chile. Figura 2. Región de Tarapacá en el norte de Chile. it floats on top and can be skimmed off, gradually remov- silver using lead. Insights from documentary sources ing lead and other impurities and finally leaving behind and an increasingly convincing body of archaeological pure silver (Tylecote 1964; Lechtman 1976). evidence, however, indicate that smelting of silver-bearing minerals with lead and the techniques of scorification and cupellation were relatively widespread in the Andes, EVIDENCE OF SILVER PRODUCTION even before the arrival of Europeans. IN THE PREHISTORIC AND COLONIAL ANDES Ethnohistoric sources for the silver production process Almost four decades ago, Clair Patterson (1971) categori- cally rejected the idea that pre-Hispanic metallurgists Descriptions of indigenous techniques of silver pro- in the Andes had developed the technique of purifying duction are primarily found in early historic sources Silver production in the Quebrada de Tarapacá / C.