Isotopic Ag–Cu–Pb record of 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, , and 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, , and the 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 -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 (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 (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 (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 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. In contrast, Fig. 2. Lead isotope compositions for Antique (n = 24), medieval (n =23), – Pb from all of the European medieval coins derives from the western Andean (n = 11), Mexican (n = 8), and 16th 18th century European (n =25) European Hercynian basement. Spanish medieval coins form two coins. Analytical errors are smaller than the symbols. distinct groups with coinage predating the Catholic Kings (1454– 1474), having 206Pb/204Pb <18.5 and therefore bearing a European > [here National Institute of Standards and Technology (NIST)

Hercynian signature contrasting with the largely 18.6 values of ANTHROPOLOGY δ65 65 63 65 63 – × the Catholic Kings samples (1479–1504), which are more similar to 976]: Cu = [(( Cu/ Cu)sample/( Cu/ Cu)standard) 1] 1,000. δ65 ‰ the values found in the Betic Cordillera district. As expected, the The Cu unit is the part per 1,000 (per mil or ). Fig. 3A shows 206Pb/204Pb ratios of coins from Spanish America are strongly the Cu isotope compositions of analyzed samples. Except for δ65 − ‰ imprinted by the rather recent magmatic activity of the Cordilleras sample (Gr2: Cu = 4.06 ), which was also anomalous for Pb δ65 − (<130 Ma) and overlap with the Antique and precolonial European isotopes, the Cu values of Antique coins range between 1.00 ‰ coins derived from the Aegean and Betic districts. 206Pb/204Pb in and +0.15 , whereas the medieval, Mexican, Andean, and – 16th–18th century European coins have δ65Cu ranging from −0.5 16th 18th century Spanish coinage varies between precolonial GEOLOGY ‰ δ65 − and Mexican values. The Pb model ages of two 17th century coins, to +1 . Cu values for medieval samples fall between 0.5 and ‰ δ65 ± ‰ one French and one English, are conspicuously young (<70 Ma). 0.5 . The range of Cu values for both Mexico (0.0 0.2 ) and Potosi (+0.7 ± 0.2‰) is particularly narrow. The δ65Cu of Copper. Isotopic data are reported in δ notation, for which the most European coins from the 16th–18th century, regardless of isotope composition is cast as the deviation of a particular iso- country, is similar to Mexican values (Fig. 3A). topic ratio with respect to the same ratio in a standard material Silver. Isotopic data are reported in parts per 10,000, (ε), with 109 109 107 109 107 ε Ag = [(( Ag/ Ag)sample/( Ag/ Ag)standard) – 1] × 10,000 with respect to the standard SRM 978a. The observed range of isotopic variations (from −1to+2 ε-units) is ∼30 times the analytical uncertainty (∼0.1ε). The Ag isotope variability of Antique coins defines two groups (Fig. 3), the oldest having ε109Ag ∼ 0.0 and the younger, mainly composed of Roman and Gallic coins, having ε109Ag ∼−0.5. The two groups are statistically different at the 99% confidence level. The ε109Ag values of the medieval, European, and Spanish coins, with the exception of the Catholic Kings coins, overlap with those of the second Antique group (Fig. 3). As in the case for Pb, the Ag isotope composition of the Catholic Kings coins also is distinct from that of the rest of the medieval coins (ε109Ag = from 0.0 to +1.5). The eight Mexican samples show very little ε109Ag variability (0.7 ± 0.2). This range overlaps with the values of two Mexican native silver ores that we measured (ε109Ag = 0.3 and Fig. 1. Map of Europe with the <90-Ma-old Alpine (in particular Aegean, 1.2), Pachuca and , two large mines actively exploited 109 Basque–Cantabrian, and Betic) domains indicated in gray overprinting the in colonial times. The ε Ag value of −5.3 reported by Hauri older western European Hercynian (250- to 400-Ma-old) basement. et al. (26) for the silver ore form Zacualpan (Mexico) is much

Desaulty et al. PNAS | May 31, 2011 | vol. 108 | no. 22 | 9003 Downloaded by guest on September 30, 2021 A 1.0 Discussion First, we assess the extent to which isotope compositions can be used to identify the source of metal ores. We review the various 0.5 processes that cause isotopic variability within a given ore de- posit, including the mass-dependent thermodynamic fraction- ation of Ag and Cu isotopes, and the variability over regional distances, which is important for Ag as well as for Pb isotopes. 0.0 Processing of coins may alter the original isotopic signatures, in particular isotopic fractionation during metallurgical processes,

Cu and willful additions or accidental contamination can overprint

65 -0.5 the original initial isotopic signature. Second, we use the Pb, Ag, δ Antique and Cu tracers to infer the provenance of the metals contained Medieval Spain Potosi within the samples analyzed in this study. Third, we examine how Catholic Kings Lima these provenance inferences relate to known historical events -1.0 Medieval Europe Mexico and what they teach us about silver circulation through the 16th– 16-18th c. Spain 18th century Spanish economy. 16-18th c. Europe -1.5 Thermodynamic Isotope Variability Among Coexisting Ores. The ex- -2 -1 0 1234 109 tent of Ag isotope fractionation among native metal and other Ag ε Ag minerals (sulfides, sulfo-antimonides, and chlorides) from a single

500 deposit or from nearby localities is not well studied, but some B inferences can be made from available data. A single observation shows that the Ag isotope compositions of coexisting pyrite and 400 native silver ore from Pribram (Czech Republic) are within error of each other (27). The conspicuous isotopic homogeneity of Mexican samples, however, makes a strong case against sub- 300 stantial thermodynamic fractionation among minerals. For ex- ample, the mining of both oxidized [colorados (red ores), inclusive of native silver, Ag chlorides and bromides, and Fe oxides] and 200 sulfidic [negros (black ores), inclusive of pyrargyrite, pyrite, ga- lena, and ] silver at the major camp of (34, 35) does not translate into measurable Ag isotopic variability 100 among the coins struck in Mexico. Pb model Age (Ma) The range of Cu isotope variation among coexisting ores is clearly larger than that for Ag (23, 24). Both Cu isotopic homo- 0 geneity and values close to zero argue for the incorporation of metal from high-temperature ores into Mexican coins, possibly bornite or chalcopyrite. Likewise, the 10 samples from Potosi have -100 δ65 ± ‰ -2 -1 0 1 2 3 4 similar Cu of +0.7 0.2 , whereas the 3 samples dated be- − ‰ ε109 Ag tween 1620 and 1670 have values between 0.3 and +0.1 . The narrow range of δ65Cu within each group signals the use of high- Fig. 3. (A) δ65Cu (in parts per 1,000) vs. ε109Ag (in parts per 10,000). (B)Pb temperature ores. model ages T (in millions of years) vs. ε109Ag for Antique (n = 20), medieval (n In contrast to the cases of Ag and Cu, lead isotope variability = 23), Andean (n = 11), Mexican (n = 8), and 16th–18th century European (n = results from the radioactive decay of U and Th rather than ther- 24) coins. Sample GR2 is not reported on this graph due to its very different modynamic fractionation. Consequently, Pb isotopes do not re- Cu isotope composition (δ65Cu = −4.06‰, see text). Errors on δ65Cu (2 SD) fl fi ε109 ect on the predominant sul de type, but mainly on the regional and Ag (2 SEM) are shown for each sample. Probability ellipses are geologic context of the ore. represented for three groups of samples: Antique and medieval coins, Mexican coins, and Andean coins. Origin of Regional Isotopic Variability. Silver. Natural silver isotope variability is very narrow (25–27) and a meaningful isotopic signal more negative. In contrast, the Ag isotope compositions of Potosi can be detected only with extremely precise measurements ± ε coins are quite variable. In the Spanish samples from the 16th– ( 0.1 ). Except for a handful of data on native silver, the isotopic 18th century, the ε109Ag varies from −1.0 to +1.0, a range that composition of silver ores is largely unknown. Native silver ores from Italy, Mexico, Canada, Russia, and Norway show ε109Ag includes both the French (0.35) and English coins (0.32). variations of ∼5 parts per 10,000 (25–27). A major finding of our Ag–Cu–Pb correlations. Fig. 3A shows that each group of coins falls work is that a substantial proportion of American Ag has isotope in a specific part of the ε109Ag–δ65Cu diagram with a few outliers. compositions that can be distinguished from those of the metal used in pre-1492 European mints. This is the case for the 8 The field of Antique and medieval coins before the Catholic Mexican coins analyzed here (ε109Ag = 0.7 ± 0.2), which are Kings plots toward the negative δ65Cu and ε109Ag quadrant. δ65 distinct from the 24 Antique and 18 medieval European coins Seven Potosi coins stand out for their high Cu, whereas three ε109Ag = −0.2 ± 0.6) (the Catholic Kings, 1479–1504, stand out ‰ δ65 ε109 ( of them have values close to 0.0 : Cu and Ag are not as an exception) (Fig. 3). In contrast to the , – correlated. Most European 16th 18th century and Mexican coins Mexican silver production was divided among several major fi δ65 ∼ ‰ ε109 ∼ plot in a narrow eld at Cu 0.0 and Ag 0.7. The Ag camps (4). The metals analyzed here most probably come from and Cu isotope compositions of Philip III Spanish coins are different deposits, yet the Mexican Ag isotope signature is dis- surprisingly similar to those of the pre-Catholic Kings medieval tinct. The spread of ε109Ag in Potosi and Antique coinage reflects samples. The only significant correlation between Ag and Pb a different situation. The geological setting of the isotopes is observed for the Antiques coins with Pb model ages mine at Potosi, which is hosted by a young (13.8 Ma) volcanic T < 200 Ma (r = −0.8) (Fig. 3B). dome intrusive into a much older (Ordovician or ∼450 Ma) series

9004 | www.pnas.org/cgi/doi/10.1073/pnas.1018210108 Desaulty et al. Downloaded by guest on September 30, 2021 of sediments, is complex (36). This complexity is apparent in the resulting amalgam was boiled off and both silver and mer- regional Pb model ages (Fig. S1). Different sources of silver may cury were retrieved. used in Spanish America came therefore be involved in the same ore deposit. In addition, dif- from three sources: the Huancavelica mines (1,500 km ferent mines contribute to the same mint. In contrast to Mexico, north of Potosi) (Fig. S1), which provided mercury to the where no particular silver mine dominated, Potosi was more viceroyalty of Peru; the Almaden mines in southern Spain, productive than the other camps in Peru, which had difficulties which supplied mainly Mexico and less frequently Potosi; with labor and capital (4). Ambiguities about the origin of silver and the Idria mines in modern Slovenia, which were tapped coins arise from both the metal registration and minting. Regis- occasionally to make up for any shortfalls from the two tered Potosi production accounts for 80% of the silver minted principal sources (12, 39). over the history of colonial Peru, but other neighboring mines, iii) Cupellation is a purification stage that separates metals eas- such as Sicasica (1600), Tatasi (1612), and Padua (1652), also had ily oxidized, typically Pb and Cu, from Ag, which remains their production registered in Potosi during the last half of the metallic. It often involves litharge (PbO) addition. This 17th century (4). The Potosi mint processed Potosi silver but also stage was used after smelting and for recycling preexisting independently registered metal from nearby mines (Porco and metals (coins and silverware) with large Cu contents. Oruro) and occasionally dealt with silver from the major and more remote camp of Cerro de Pasco whenever the Lima mint closed For the metallurgical process to induce isotope fractionation, down (Fig. S1). The spread of Ag isotope compositions of the it must cause partial vaporization of the metals or involve a solid Antique coins also calls for multiple sources of metal: ε109Ag or a liquid phase that coexists with the metal, notably silicate-rich correlates with Pb model ages T (r = −0.8 if the three samples with slag or Pb-rich oxides. Because little isotope fractionation of T > 200 Ma are disregarded). The ore deposits therefore tap a stable metal isotopes is expected at the high temperatures of very young geological source (T ∼ 0) of metal with ε109Ag ∼ 0.0, metallurgy, the yield has to be poor for isotope fractionation to mostly represented by the coins from the eastern Mediterranean be observed. Baron et al. (37) concluded from smelting experi- Basin on the one hand and metal from the older basement (T > 200 ments that the Pb isotope signature of ores is preserved during 109 fi Ma) mostly represented by Roman and Gaelic coins (ε Ag ∼−0.5) metallurgy. Likewise, Cu extraction and re ning processes do not on the other hand. alter the copper isotope signature of copper ores (40). For Ag, Copper. As noted before, the δ65Cu values separate most Potosi no effort was spared to keep the yield as high as possible, and coins from the rest of the corpus. Because copper isotope com- hence any potential isotope fractionation of Ag was minimized. positions are controlled by ore genesis, it is unlikely that δ65Cu is The homogeneity of Ag isotopic compositions in Mexican coins a true regional variable. Despite this, our observations indicate and their similarity with those of local ore suggest that frac- that the Potosi mint was using copper that came from an iso- tionation related to metallurgy is weak. The spread topically well-defined, but unidentified ore deposit. We therefore in Mexico starting in the 1550s while smelting and silver recovery consider δ65Cu of ∼ +0.7‰ as a geographically meaningful tracer by lead cupellation still persisted. Smelting was largely used in of Potosi copper. the late 17th century due to a shortage of mercury in Mexico (4) Lead. The Pb model ages T of the samples (Table S1 and Fig. 3B), and was in general preferred for the treatment of Ag-rich ores, and to a large extent the 207Pb/206Pb and 208Pb/206Pb ratios, are which was the case of Pb ores (34). Poor miners and Indian laborers, who received part of their wages in ore (39), also fa-

reliable indicators of the geological age at which the crustal vol- ANTHROPOLOGY ume that gave rise to a particular ore body was isolated by geo- vored it. Until the 18th century, it has been estimated that dynamic processes. For example, the 206Pb/204Pb ratios of the roughly half of the silver produced in Mexico came from the European Betic, Mexican, and Andean districts, which all derive smelting process (4). Extractive metallurgy, whether smelting or fi from young provinces (<130 Ma), are similar and distinct from amalgamation, is therefore not a signi cant source of Ag isotope those derived from Hercynian northern Spain and western variability. This assessment may not be valid for Peru, where it is Europe, where crust mostly formed 250–450 Ma. Thus, it is dif- known that yields were poor (4). Use of additives during metallurgical processes or recoinage

fi GEOLOGY cult to use Pb model ages T (or, equivalently, Pb isotope ratios) fi to distinguish coins from southern Spain from those of the New (37, 41) is expected to distort ngerprinting if the additives and 207 204 fi the ore have a different origin. Likewise, litharge (PbO) addition World. Other ratios, such as Pb/ Pb, may ngerprint old fi Precambrian crustal segments, such as the Andean Altiplano (21), during postsmelting puri cation by cupellation may overwhelm 208 204 206 204 fl the original Pb isotope signature. Such problems are particularly whereas Pb/ Pb variation relative to Pb/ Pb re ects the fi poorly understood variability of Th/U ratios among source rocks. serious if mining, ore treatment, and metal puri cation take place One possible interpretation of the spread of Pb model ages T and at different locations. In the patio process, the many additives are 206Pb/204Pb ratios observed for Potosi coinage, and that contrasts a concern, notably mercury. The Pb content of mercury and cinnabar is not recorded, but given the solubility of lead, both in with the homogeneity of Pb in Mexican coins, is the mixing of ∼ modern Pb from the Cerro Rico volcanics with Pb from the old mercury and in silver ( 1%) (42, 43), amalgamation may have sedimentary basement. altered the Pb isotope composition with respect to the original ore. In addition, lead contamination by cupellation is expected fi Effects of Extractive Metallurgy, Recycling, and Coinage. Different during the re nement frequently required before recoinage (44). processes were involved in the extractive metallurgy of silver: Accession of new monarchs, design of new coins, silver import, and coinage debasement were all opportunities to introduce i) Smelting consists of heating the metal ore, possibly after foreign Pb into the metal. New World silver reminted in Spain is a first stage of roasting, with a reducing agent, commonly expected to involve European lead and to obscure the American charcoal. During the medieval period, some metallic Pb was Pb isotope signature of the metal. Likewise, Andean and Mexican added at the beginning of the smelting process to facilitate silver went through multiple recoinage in the Americas (1728, the recovery of Ag directly from (37). 1772, and 1786) (17), but local reprocessing is less likely to cor- ii) After the 1550s in Mexico and the 1570s in Peru, the kind of rupt the isotopic signature. amalgamation known as the patio process of silver extraction The purpose of copper alloying is either improved coin allowed silver recovery from very low-grade ore. The ore hardness and resistance (∼5–10%) or debasement (17). In gen- was first finely crushed. Added to this ore were large quan- eral, Pb and Cu ores form in different environments (13). Pb tities of common table salt (NaCl), vitriol (CuSO4 and contents in chalcopyrite are rather limited and, for fine silver FeSO4), known as magistral, and mercury, with a typical coins, Pb contamination associated with Cu addition should be ratio of lost mercury to silver produced of 1.5 (38). The less important than during purification. The Ordinance of Me-

Desaulty et al. PNAS | May 31, 2011 | vol. 108 | no. 22 | 9005 Downloaded by guest on September 30, 2021 dina de Campo (1497) defines the weight of the Real (3.434 g) ES48, and ES45) all have δ65Cu at ∼0.0‰. With the exception of and stipulates that it contains 3.195 g of silver (93% Ag and 7% the intermediate ES40, this group of coins also has negative Cu) (45). The use of Cu isotopes to trace Andean and Mexican ε109Ag. These characteristics do not fit American metal supply silver in Spanish colonial coins is relevant only for exports con- and can be explained by the alloying of pre-1492 silver with Pb of sisting of silver coins. Otherwise the copper signature is inherited local origin. Both Charles V and Philipp II coins have Hercynian from wherever copper was added, possibly in Europe. According Pb model ages T (287 and 247 Ma, respectively). The Pb model to Garner (14), if there is little doubt that silver was exported in ages T of the Philipp III coins are consistent with the locality of different forms, coins were the favorite one. Although up to the mint: ES19 (39 Ma) and ES21 (36 Ma) were struck in Seville, a few percent metallic Cu can be alloyed with Ag (46), silver of whereas ES45 (268 Ma) was struck in Valladolid. The Toledo lower fineness is prone to unmixing and, during oxidative high- sample (ES48, 147 Ma) is intermediate. In contrast, from Philipp temperature reprocessing, to oxidation (47): Removal of Cu by V (1700–1746) onward, silver isotopes (ε109Ag ∼ +0.7) un- cupellation is then necessary before realloying. Coinage recycling ambiguously demonstrate the prevalence of Mexican silver in the preexisting coins can therefore be suspected to contain copper Spanish monetary mass of the 18th century. The observation that freshly added at the site where recycling took place. few Spanish colonial coins have Pb model ages T as young as those of Potosi and Mexico does not imply that Spanish silver was Provenance Assessment. Antique and pre-1492 European coins. Most not imported from the Americas. Rather, it emphasizes wide- Antique coins are characterized by young Pb model ages T and spread recoinage and refining, which mostly used local European low (<0.1) ε109Ag values. The very young Pb model ages T of the lead. The δ65Cu and ε109Ag of the 17th century French and En- silver coins from the eastern Mediterranean area (with ε109Ag ∼ glish coins and their young model ages point to a strong contri- 0.0, see above) are consistent with the prevalence of either local bution of Mexican metals (Fig. 3). metal sources or sources in the Betic district in Southern Spain (33). The intermediate (∼100 Ma) model Pb ages T of the Roman Silver Circulation. The Spanish quest for silver in the New World and Gaelic coins are geologically unusual and suggest that mixed started as early as 1498 (53), but it was only in the early to mid- sources of Pb were used in silver metallurgy. In contrast, most 16th century that the major mines were opened (4). European European medieval and a handful of Roman coins are charac- Spanish coins from the 16th and early 17th centuries (Charles V terized by Pb model ages T older than 200 Ma and negative to Philip III) show no input of American metal, which suggests ε109Ag isotope compositions. Clearly, Antique silver either is that coins and cobs struck in Mexico and Peru were not realloyed a minor component of the medieval silver monetary mass or has into Spanish coinage. Of the silver mined in the Americas, 20% been largely reprocessed using old Hercynian Pb. A puzzling case stayed on the continent (12). Another 10% were used to buy is that of the coins of the Catholic Kings (1479–1504), in which Asian silk, porcelain, and spices (14), and yet another 15% fell in the young Pb model ages T (28–120 Ma) reflect the prevalence of the hands of pirates or was smuggled (15), leaving ∼200 tons to a Betic metal (20, 31, 32). This period corresponds to the capture reach Seville every year of the late 1500s and early 1600s (4, 5, 9). of the kingdom of Granada and of its rich Ag mines by the Philip II defaulted on the Spanish debt in 1557, 1560, 1575, and Spanish kings. The scatter of ε109Ag for the Catholic Kings coins 1596 (54, 55) and reopened the Rio Tinto and other Spanish is uncharacteristic. The only coin of the Catholic Kings (ES32) silver mines (56), which confirms that American silver did not stay with a Hercynian signature was struck in a northern mint at in Spain very long. As stated by Braudel (ref. 57, p. 205) “every Burgos, whereas the other coins were struck in Seville or Granada consignment of American silver was quickly dispersed in all in southernmost Spain. directions, almost like an explosion.” Silver was mostly exported Mexico. The ε109Ag of Mexican coins is very similar to native silver from Spain to repay the huge loan obtained from the German from Pachuca and Guanajuato, two large mines exploited by the bankers to secure Charles V’s election and to repay Genoese Spaniards, analyzed in this study (+0.3 and +1.1, Table S1), but bankers for other major loans. It was also lost to subsidize the differs from the value of −5.3 ± 0.5 found by Hauri et al. (26) for wars in The Netherlands; to buy grains, cloth, and paper that Zacualpan. This difference suggests that Zacualpan silver was not Spain did not produce itself in sufficient quantities; or simply used for coins analyzed so far. The Pb isotope compositions are because petty money was driving out good silver (16). However, consistent with what is known of the Mexican sulfide ores in the the absence of the New World treasures from Spain is not suffi- region of colonial Spanish mining in the center and the north of cient to reject their role in the Price Revolution. According to the country (48, 49). Flynn (10), the influx of American silver may have had a global Andes. The only available ε109Ag value from a local mine (Porco, influence on international markets and may explain Spain’s in- Table S1) falls within the range of Potosi coins. Likewise, the flation as a reflection of the overall European Price Revolution. isotope composition of Pb present in the coins struck in Potosi is Our isotopic data on the coins of Philip V (1700–1746) indicate consistent with literature values for the neighboring Ag ore that Mexican silver found its way to the Spanish silver monetary deposits of Cerro Rico, Oruro, and Porco (ref. 50 and references mass only in the aftermath of the Utrecht treaty (1713), which therein) (Fig. S2). In contrast, the Pb isotope composition of Cerro marks a major break in Spanish involvement in foreign wars, de Pasco next to Lima is clearly different (51, 52). The spread of Pb which in turn coincides with the onset of a major phase of silver isotope compositions requires the contribution of a rather old end mining expansion in America (4, 5, 58). These data also show that member, which can be European Pb introduced by amalgamation, the isotopic signature of European silver until Philip III (1598– local Pb from the Paleozoic basement, or possibly an unknown 1621) is not detectable in Philip V coins. If the corpus analyzed in source (Fig. S2). The two samples PotoD and PotoF with the the present work is a representative sample of the contempora- oldest Pb model ages T (329 and 252 Ma, respectively) and also neous metal, the implication is that by the time of Philip V, distinctly high ε109Ag (+1.6 and +3.3) suggest that they represent Mexican silver had actually replaced the silver monetary mass a local variation rather than contamination or isotope fraction- circulating under Philip III, which was partly exported and ation during the amalgamation process. For the rest of the Potosi partly diluted. coins, compelling evidence for what created the Ag isotope vari- ability is missing. Whether a low yield of the extractive metallurgy Conclusions or regional isotopic variations, the Ag isotopic signature is het- This work demonstrates that silver isotopes can be used suc- erogeneous and not particularly distinctive. cessfully to trace the origin of coinage. The usefulness of Pb European 16th–18th century coins. The Spanish vellón coin ES4 of isotope compositions as tracers can be strengthened by using Charles V (1516–1555), the half-real ES40 of Philipp II (1556– model ages T, which represent a geologic characteristic of ore 1598), and four coins of Philipp III (1598–1621) (ES19, ES21, deposits, but is made ambiguous by silver purification and

9006 | www.pnas.org/cgi/doi/10.1073/pnas.1018210108 Desaulty et al. Downloaded by guest on September 30, 2021 reprocessing, which often involve local sources of Pb distinct mass bias. Details relative to sample preparation and MC-ICPMS measure- from the ore sources. The combined use of Ag, Cu, and Pb can ment protocols are provided in SI Materials and Methods. distinguish pre-1492 European silver from Mexican and Andean ACKNOWLEDGMENTS. We thank Jacques Samarut, Chantal Rabourdin- metal sources. European silver dominated Spanish coinage until Combes, Dominique Le Quéau, and Mireille Perrin. We thank all the profes- Philip III but, 80 years later under the reign of Philip V, had been sional numismatic dealers around the world who provided the coins and, in flushed from the monetary mass and replaced by Mexican silver. particular, Daniel Sedwick from Orlando for expert advice. Florian Tereygeol kindly gave two Andean samples and George Rossman Mexican ores. We thank Merlin Méheut and Ghylaine Quitté for informal discussions and Maia Kuga, Materials and Methods Chantal Douchet, and Aline Lamboux for their friendly help in the laboratory. The corpus is composed of 94 samples described in Table S1. After cleaning, Janne Blichert-Toft provided expert, quick, and generous help by editing the a piece of coin was cut off with pliers and dissolved in nitric acid. Ag was text. An anonymous reviewer is particularly thanked for detailed comments and useful suggestions. This work was supported by the Institut National des precipitated by addition of ascorbic acid. Cu was separated in HCl medium Sciences de l’Univers and Ecole Normale Supérieure. Late but critical support by and Pb in HBr medium on anion exchange columns and then analyzed by the program CIBLE (Créativité-Innovation-Projets blancs) funded by the Région MC-ICPMS (22), using Pd (Ag), Zn (Cu), and Tl (Pb) to correct for instrumental Rhône-Alpe helped us acquire high-quality material.

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