Biogeosciences News

Fresh Take on a Gold Treasure’s Origins Using Geochemistry

Blending geoscience and archaeology, researchers apply a new technique to pinpoint where ancient and unique gold artifacts were crafted.

By

The Treasure of El Carambolo, a collection of 7th century BCE gold jewelry, has provoked archaeologic debate for decades. Since its accidental discovery 60 years ago inside a vase near Seville, Spain, studies of the ancient jewelry have suggested two conflicting stories of origin set thousands of kilometers apart. Recently, researchers used techniques more commonly found in the geosciences to try to locate precisely where the gold was mined and have come up with a third option.

“The origin of the gold need not be from thousands of kilometers away, in the Atlantic or eastern Mediterranean,” said anthropologist Francisco Nocete of Universidad de Huelva in Spain and lead researcher on the new analysis. Instead, Nocete’s analysis suggests a much more local origin for the gold: the ancient economic and political hub of Valencina de la Concepción, located a mere 2 kilometers from El Carambolo.

Nocete and his team used a combination of laser ablation mass spectrometry and lead isotope analysis to get detailed geochemical measurements of the treasure without damaging or altering the valuable artifacts. The researchers compared the Carambolo measurements with those from other artifacts discovered on the Iberian Peninsula. They found that the Carambolo gold is chemically similar to gold artifacts created at Valencina de la Concepción nearly 2,000 years earlier, which suggests that the Carambolo Treasure used the same gold source.

Geoscientists commonly use these same techniques to measure the elemental composition and age of a solid sample, like a rock or a fossil, without significantly altering the sample itself. In this Carambolo research, which was published last month in the Journal of Archaeological Science, scientists for the first time have used the combined techniques to trace the provenance of archaeological artifacts of unknown origin.

A Controversial Past

The Carambolo Treasure was discovered in 1958 in the Camas region near Seville. Archaeologists initially linked the gold treasure, which consists of 21 intricate jewelry pieces, to the prosperous and metal-rich Tartessos culture. Tartessos spanned the southern coast of the Iberian Peninsula (near what is now Andalusia, Spain) from the 9th to 6th centuries BCE.

However, the treasure’s design recalls the Phoenician style of the time, and the hoard came from what had been a Phoenician temple. Phoenicia, an eastern Mediterranean civilization and a trade partner with Tartessos, built a few colonies along the Iberian coast.

With Tartessian and Phoenician influences, archaeologists wondered whether Phoenicians mined and shaped the gold and then brought it to Tartessos or whether Phoenician-influenced artists mined and created the jewelry set in Tartessos. Once determined, the gold’s origin will tell us more about why the set was created and what it was used for, archaeologists said.

Modern Methods, Ancient Artifacts

Despite the controversy about the Carambolo Treasure’s origin and purpose, researchers have hesitated to use classical analysis techniques on the hoard, fearing it would damage the unique and valuable artifacts, explained Sonia García de Madinabeitia in a press release about the research. García de Madinabeitia, a mineralogist and petrologist at the University of the Basque Country in Vizcaya in Spain, helped perform the new analysis on the gold.

Dolmen de la Pastora in Valencina de la Concepción
Dolmen de la Pastora, a monolithic stone tomb in Valencina de la Concepción in Seville, Spain. The similar chemical compositions of the Carambolo Treasure and of older gold artifacts found in and around Valencina de la Concepción suggest that the artifacts are made from gold from the same as yet unidentified source. Credit: Cazalla Montijano, Juan Carlos (Instituto Andaluz del Patrimonio Histórico), CC BY-SA 3.0

To gain a new perspective on the treasure’s provenance, Nocete’s team extracted 100-micrometer-diameter samples from two of the Carambolo pieces using laser ablation. They then used mass spectrometry to identify the composition of tiny impurities—silver, copper, lead, zinc, and platinum—in the gold.

Combined with a lead isotope analysis of the samples, the chemical impurities make up a “signature” of the gold, which the team could then quantitatively compare with other treasures or gold mines. The modern techniques have the “minimum possible impact” on the artifacts, said García de Madinabeitia.

The team found that the two Carambolo pieces they tested likely came from the same source of gold. If those two pieces are representative of the entire set, this result supports the long-held assumption of archaeologists who have studied the treasure that the set all comes from one place.

More Clues in the Gold’s Chemical Fingerprint

The team then compared the Carambolo measurements with those of artifacts discovered across the Iberian Peninsula that date to the same period and also with those of artifacts that are 2,000 years older, which the team had dated in a prior study. The researchers found the composition of the gold itself to be similar to that of items from a well-studied nearby archaeological site called Valencina de la Concepción. The 3rd millennium BCE site “behaved like a gateway for raw materials of regional and transcontinental origin…and as a space for artisanal transformation into products, including gold metallurgy,” said Nocete.

In other words, the study shows that the gold in Carambolo was likely shaped in Valencina de la Concepción but mined—along with other gold found at that site from an earlier era—at some unknown location.

“The most remarkable [aspect of the research] is the methodological issue and the new options that this opens for future research,” said Ignacio Montero Ruiz, an archaeologist and archaeometallurgy researcher at the Center for Human and Social Sciences in Madrid, Spain.

Nonetheless, Ruiz, who was not involved with this research, said that the findings of Nocete’s team would have been stronger had the team analyzed more than two Carambolo pieces. Such analysis could have provided clues to the gold’s region of origin, wherever it may be, he explained. He also suggested that future research should look into the possibility of even more diverse origins for the gold.

Toward a Database of Gold

This blending of geochemistry and archaeology is nothing new to Nocete and his interdisciplinary research group.

“Geochemical and isotopic studies have been part of our methodology” since their research group formed in the early 1990s, he explained. “These chemical and isotopic techniques were already known [in] the 80s,” Nocete said, but he and his team pioneered their combined application to archaeological gold to learn more about the artifacts’ history.

Nocete plans to keep improving this analysis technique to minimize the impact of testing methods on other artifacts. The researchers are also working to compile a database of natural gold sources on the Iberian Peninsula and hope to expand to other areas of Europe, as well as to Asia, Africa, and South America.

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

Citation: Cartier, K. M. S. (2018), Fresh take on a gold treasure’s origins using geochemistry, Eos, 99, https://doi.org/10.1029/2018EO099525. Published on 21 May 2018.
Text © 2018. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.