Geochemistry and economic history

At first reading this item’s title might seem to convey nonsense, yet there is an interesting relationship between these two very different disciplines. It concerns the pillaging of South and Central America by conquistadors who followed Columbus’s pioneering route across the North Atlantic in 1492. Aside from glory their motive was profit, and that was most conveniently concentrated in the form of gold and silver, to be found in abundance among the native people of what came to be known as the Americas. Once such plunder declined silver ores were soon discovered in Peru and Mexico, thereby maintaining the supply. Bullion or plate – so named from the fact that precious metal was most often transported in the form of sheets – was the major cargo of the great treasure ships in the period from 1515 to 1650. It is remembered in such geographic names as the Rio de la Plata separating modern Argentina and Uruguay.

Werner Herzog and Klaus Kinski shooting "...
Klaus Kinski, well into his role as an insane conquistador, disputes the script with director Werner Herzog while shooting “Aguirre, The Wrath Of God” (credit: Flickr p373)

It might seem that when such a vast amount of loot entered Europe the buying power of silver in particular would have fallen to result in inflation in the price of basic commodities, much as printing paper money may have that result nowadays. Indeed, over those roughly 150 years prices increased by as much as five times. Another factor was a tendency for silver supply to be augmented simply by debasing newly minted currency with other metals. Yet another is that over the same period China adopted silver as a money commodity increasing demand and so spurring exploration and advances in metallurgical extraction from new ores. Furthermore, the entire fabric of economy in Europe began to shift as feudalism began to be supplanted by capitalism at the close of Medieval times. The sheer complexity of competing factors has made the so-called ‘Price Revolution’ of the 16th and 17th centuries a thorny issue for economic historians. This is where geochemists found that they had a ‘shout’ in what Thomas Carlisle dubbed the ‘dismal science’.

Silver ores also contain lead and copper, which inevitably contaminate silver metal extracted from them. Depending on the processes involved in mineralisation the abundances of both metals vary from mine to mine. More tellingly, so do the relative proportions of the different Pb and Cu isotopes, Pb isotopes reflecting the age of the rocks in which ores are found. Inherited by coinage, the isotopes can be used to assess provenance of coins (Desaulty, A.-M. & Albarede, F. 2013. Copper, lead and silver isotopes solve a major economic conundrum of Tudor and early Stuart Europe. Geology, v. 41, p. 135-138), while the dates embossed on coins at the mint potential chart the course of the bullion trade. Desaulty and Albarede show that silver from the vast Potosí mine in modern Bolivia opened by conquistadors barely shows up in British coinage of the period, which is dominated with Mexican isotopic signatures as well as those from European mines. The latter account almost exclusively for the coinage of the late Medieval period. The conclusion is that the huge potential of Potosí served the needs of Spanish entrepreneurs though a trans-Pacific Spanish trade in which Bolivian silver bought goods from China, including gold. Spanish coins, on the other hand, show little of either Bolivian or Mexican silver, suggesting that Spanish world trade may well have used American bullion directly to purchase goods throughout its sphere of influence centred on the Philippines, while Mexican silver engaged in European trade and also found its way into the British economy by way of the slave trade.

Although Desaulty and Albarede claim to have solved a ‘conundrum’ it seems more likely that their revelations will make historians of post-Medieval economics scratch their heads even more.

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