Isotopic Ag–Cu–Pb Record of Silver Circulation Through 16Th–18Th Century Spain
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Isotopic Ag–Cu–Pb record of silver circulation through 16th–18th century Spain Anne-Marie Desaultya,b,c,1, Philippe Telouka,b,c, Emmanuelle Albalata,b,c, and Francis Albarèdea,b,c aEcole Normale Supérieure de Lyon, F-69342 Lyon, France; bUniversité de Lyon, 69622 Villeurbanne, France; and cCentre National de la Recherche Scientifique, UMR 5276, 69364 Lyon Cedex 07, France Edited* by Donald J. DePaolo, University of California, Berkeley, CA, and approved April 13, 2011 (received for review December 6, 2010) Estimating global fluxes of precious metals is key to understanding other, which often makes provenance assignment insufficiently early monetary systems. This work adds silver (Ag) to the metals (Pb discriminating. More recently, the high precision of the multiple- and Cu) used so far to trace the provenance of coinage through collector–inductively coupled plasma mass spectrometry (MC- variations in isotopic abundances. Silver, copper, and lead isotopes ICPMS) technique (22) allowed Cu isotopes to be added to the were measured in 91 coins from the East Mediterranean Antiquity coinage tracers and a number of successful applications to the and Roman world, medieval western Europe, 16th–18th century identification of the sources of metals used for coinage have been Spain, Mexico, and the Andes and show a great potential for prove- suggested (23). Although copper is primarily alloyed with coinage nance studies. Pre-1492 European silver can be distinguished from silver to improve metal hardness and resistance, it was also used for Mexican and Andean metal. European silver dominated Spanish coin- monetary debasement (17). Copper has two stable isotopes of mass age until Philip III, but had, 80 y later after the reign of Philip V, been 63 and 65, and, in contrast to the large variations in radiogenic Pb flushed from the monetary mass and replaced by Mexican silver. isotope abundances, which are due to the radioactive decay of U and Th, the abundance variability of Cu isotopes is due exclusively silver coinage | Spanish Americas | Price Revolution | MC-ICPMS to the physico-chemical conditions of ore-forming processes (pri- mary hydrothermal sulfides vs. low-temperature sulfides and hydrocarbonates) (23, 24) and remains within a few parts per 1,000. particularly momentous time during the early history of The other multi-isotopic coinage metal is silver (Au is mono- Amodern European economy was the attempt by Hamilton isotopic), but beyond some preliminary data on silver ores (25–27) (1) to demonstrate that the great Price Revolution (1520–1650) fl no archeological application has been attempted. Silver has two was largely fueled by the in ux of American silver rather than naturally occurring isotopes, 107Ag (51.4%) and 109Ag (48.6%). by widespread coinage debasement and minting of the low- Evidence of 0.5‰ Ag isotopic variability among silver ores (25–27) denomination copper “vellón”. The idea connecting silver influx 109 107 fl provides a strong incentive to use the Ag/ Ag ratio as a prov- to European in ation was actually proposed as far back as the16th enance tracer despite the need for time-consuming high-precision century by the French philosopher Jean Bodin (2) and is com- ∼ isotopic analysis. monplace in classical economics. Huge amounts of silver, 300 t With the incentive that the input of American silver into the – annually (3 5), were mined in the Spanish Americas from the 16th European monetary mass may be visible in the isotopic abun- to the 18th centuries. That much silver could not be absorbed dances of metals used for coinage, this work presents Pb, Cu, and locally by the American economy and therefore headed for the Ag isotope data on silver and billon coins from Europe and the European market through major Spanish harbors (6), notably Spanish Americas. We first analyzed reference material from the Seville (7), and to the Far East either directly through the Phil- Antique world (Greek, Hellenistic, Roman, Near Eastern) and ippines or indirectly through Europe (8). The thesis that the Price medieval times, notably pre-Columbian Spain. We then analyzed fl Revolution in Spain was fueled by the in ux of American silver the isotope compositions of Pb, Cu, and Ag in 16th–18th century – has, however, become controversial in recent literature (9 11). American coinage from Mexico and South America and com- More specifically, some authors emphasized that the arrival of pared them to the isotope compositions of European Spanish American metals (ca. 1550 to ca. 1809) does not coincide with the coins of the same age. We discuss the problems associated with period of inflation (ca. 1520 to ca. 1650) (9–11). Understanding the allocation of the coinage metals to potential sources, notably silver monetary mass and circulation relies on three types of pri- isotopic modification during the metallurgical processes. We also mary data: (i) the register of taxes collected when the silver bars discuss how these data can elucidate the history of the monetary received the royal stamp (the Quinto in Peru and the Diezmo in mass and circulation in the world. Mexico) (12, 13), (ii) the register of the European harbors used to import the silver shippings (1), and (iii) the compilation of con- Results temporaneous gazettes (9). These data are imprecise or even in- The analytical techniques are described in SI Materials and Methods complete, especially for trade registers between 1660 and 1809 and the data are listed in Table S1. In the following, we first examine (9), and do not take contraband and piracy silver into account the isotopic results one element at a time and then describe how the (8, 14–17). In addition, any memory of the origin of the metal is data for different elements correlate with each other. lost by recoinage, whenever silver is exported or a new king comes to power, or upon debasement. Reliable tracers of the monetary Lead. Lead has four isotopes, the stable 204Pb and the radiogenic mass and exchange that can see through the destructive alter- 206Pb, 207Pb, and 208Pb produced by radioactive decay of 238U, ations of coinage silver therefore are needed. Over the last 30 235U, and 232Th, respectively. The choice of plots used to rep- years, lead isotope compositions of metallic ores have been col- lected and gathered into large databases and broadly used as a tool for provenance studies of archaeological artifacts (18–20). Author contributions: A.-M.D. and F.A. designed research; A.-M.D. and P.T. performed The main factors of provenance analysis are (i) the contrast between research; E.A. contributed new reagents/analytic tools; A.-M.D. and E.A. analyzed data; ores produced by mantle-derived magmas with low 207Pb/204Pb, such and A.-M.D. and F.A. wrote the paper. as in Cyprus, southern Spain, and the Andes, and those produced The authors declare no conflict of interest. 207 204 in geologically ancient crust with high Pb/ Pb (such as mag- *This Direct Submission article had a prearranged editor. matism from the Altiplano) (21) and (ii) the age of the crustal 1To whom correspondence should be addressed. E-mail: [email protected]. provinces from which the Pb ores were extracted. Unfortunately, This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. the Pb isotope ratios of ores are strongly correlated with each 1073/pnas.1018210108/-/DCSupplemental. 9002–9007 | PNAS | May 31, 2011 | vol. 108 | no. 22 www.pnas.org/cgi/doi/10.1073/pnas.1018210108 Downloaded by guest on September 30, 2021 resent the data is particularly important: The traditional Antique Potosi 207 204 206 204 208 204 206 204 39.20 Pb/ Pb vs. Pb/ Pb, and Pb/ Pb vs. Pb/ Pb dia- Medieval Spain Lima grams have a long history in geochemistry and are based on the Catholic Kings Mexico well-understood control by the age of the ore and the U/Pb and Medieval Europe Th/Pb ratios of its source (crust vs. mantle). In contrast, arche- 16-18th c. Spain 208 206 Pb 38.80 ologists (28) favor different plots, notably Pb/ Pb vs. 16-18th c. Europe 204 207Pb/206Pb, which reduce the analytical noise by removing the correlations induced by relatively higher counting errors associated Pb/ with the low abundances of 204Pb. However familiar these plots 208 may be, those used for archeological purposes are more difficult to 38.40 relate to the geological history of the ore source, a particularly important parameter because the Aegean, the Betic (southern Spain), and the American Cordilleras formed <120 Ma and are still 38.00 geologically active, whereas most of Central Europe is underlain by 15.75 Hercynian basement (250–400 Ma) (Fig. 1). The “model ages” T listed in Table S1 were calculated with the common Pb isotope 238 204 composition and the U/ Pb of the crust (29, 30) using the 15.70 formula given in SI Materials and Methods. As shown in 207Pb/204Pb–206Pb/204Pb and 208Pb/204Pb–206Pb/204Pb space (Fig. 2), 207 204 208 204 Pb/ Pb and Pb/ Pb ratios are higher in Antique and Pb Potosi coins than in Mexican and European medieval coins, which 204 15.65 206 204 surprisingly overlap. The Pb/ Pb ratios of most Antique silver Pb/ coins are derived from isotopically young provinces (<120 Ma) 207 and fit sources within the Aegean, Asia Minor, and southeastern 15.60 Spain (Betic Cordillera) (20, 28, 31, 32) (Figs. 2 and 3). The Basque–Cantabrian basin is also a suitable source but its Ag pro- duction was relatively minor (33). Exceptions are Gr2, a 500 BC 15.55 Iona Miletos diobol; R118, a 118 BC Licinus Crassus denier from 18.00 18.20 18.40 18.60 18.80 19.00 the Narbo mint in Gaul; and R121, a 121 BC denier of Caius Plutius 206 Pb/ 204 Pb from the Rome mint, which probably all derived their Pb from Hercynian (∼300 Ma) ores of the European basement.