T22d - The Nebra Sky Disk and its link to Cornish gold

Date : 30/06/2024    Time : 15:30 - 16:15Gregor Borg

Location : SW 67474 41190 - Kernow Resilience Hub (conference base)

Details : 

What would the Nebra Sky Disk be without its golden "objects"? Even as an archaeological find, it would likely be little more than a green-patinated bronze Disk. We cannot escape the impact of gold, its colour, lustre, and shapes, regardless of whether we understand the pictorial program. Therefore, it is not surprising that questions about the composition and origin of the gold play a central role in the research of the Nebra Sky Disk. Native gold occurs in many rivers and creeks throughout much of Europe. But in order to compare the geochemical composition of an artefact, e.g. the Sky Disk of Nebra, one needs a database of the composition of natural gold from as many locations as possible.

Geochemical analyses confirm that the gold on the Nebra Sky Disk has a unique composition: it contains a very high proportion of silver, consistently high levels of copper and tin, and for artifact gold, anomalous concentrations of zinc, arsenic, tin, tungsten, lead, nickel, cobalt, platinum, and palladium. The particularly high silver and distinct tin content point to a tin-bearing region of origin where the gold was transported only briefly in the river, thereby being cleansed only minimally of its original companion metals from the primary veins by selective dissolution in river water.

However, what could the analytical results of the gold composition be compared to? Initially, there were no Germany- or even Europe-wide analyses of natural gold occurrences, neither for primary gold from gold-bearing veins nor for secondary gold from streams and rivers, i.e., gold nuggets. Nevertheless, there existed already a gold database detailing the composition of Bronze Age artifacts from all over Europe. Based on these artifact analyses, various types of gold were distinguished, with one subgroup exhibiting a similar composition to the gold on the Nebra Sky Disk. The gold artifacts of this group are found in the area of present-day Germany and neighbouring countries, and, with a single object, in Cornwall, Great Britain. While at first attaching little importance to the artifact from Cornwall, finds in Germany initially suggested that such gold, and consequently the gold on the Nebra Sky Disk, might originate from gold-bearing streams and rivers closer by in Thuringia, the Alps, or Bohemia.

To make such comparisons possible, funding from the German Research Foundation allowed for the sampling and analysis of natural gold occurrences across Europe as part of a multi-year research project (DFG-FOR 550). This provided a geochemical database for the composition of natural gold from approximately 100 sites for comparisons with artifact gold. The research results of the initial project years were quite sobering, as no gold from the gold occurrences in Germany and the surrounding areas matched geochemically with that of the Nebra Sky Disk; thus, it could not have originated from there. Promising gold regions, such as the gold of the River Schwarza in Thuringia, the River Rhine, or gold from Bohemia and Moravia, had to be excluded as sources. Even the natural gold from more distant gold-rich regions, such as the Golden Triangle in Romania or the Tauern gold in the Austrian Alps did not geochemically match the gold on the Nebra Sky Disk.

Finally, the search for geochemically matching natural gold led us to Cornwall. The gold nuggets from Cornwall, especially those from the Carnon River, exhibit the greatest geochemical similarity to the gold on the Nebra Sky Disk and to the initially overlooked gold cup from Rillaton Barrow relatively nearby.

The Carnon River is historically known for its rich alluvial and primary cassiterite (tin ore) deposits, which were demonstrably mined in the Bronze Age. Archaeological evidence shows that mining of tin (and gold) from the alluvial sediment fill of the Carnon River valley took place in the Bronze Age as documented by the excavation of a deer antler pick, C14-dated to the 16th century BCE (Timberlake/Hartgroves 2018). Almost as a by-product of tin extraction from river sediments, large and small gold nuggets were repeatedly found, with their extraction also historically documented. Some particularly large and beautiful gold nuggets are exhibited in the Royal Cornwall Museum in Truro and in the private collection of the Williams family in the picturesque Caerhays Castle on the British Channel coast. The Williams family operated tin (and incidentally gold) extraction from alluvial sediments of the Carnon River for more than 20 years at the beginning of the 19th century. Some of the impressive gold nuggets in the Williams Mineral Collection contain clearly visible inclusions of hard cassiterite, which were "kneaded" into the softer gold during turbulent transport in the river, thus remaining visibly preserved.

Thus, the questions remained as to why there is such unique natural gold only in this relatively small region in Cornwall and why precisely this gold was traded and processed over such great distances in the Bronze Age. The special composition of the Carnon gold is explained by the unique geological situation of the region. Metals such as gold, silver, copper, tin, tungsten, and lead were mobilized from granitic magmas during orogenic mountain formation about 280 million years ago. The intruded magmas heated deep waters in the surrounding rocks, leaching additional gold and copper, as well as other metals such as cobalt, nickel, platinum, and palladium, from surrounding amphibolitic country rocks, the surrounding metasediments not being a favourable metal source, except maybe for some traces of lead and zinc. This unusual granite-amphibolite metal association formed richly mineralized polymetallic multistage vein sand breccia systems with sulfide and oxide minerals. These later weathered near the surface, with some of the contained metals being "incorporated" into the newly formed native gold in veins, which evolved into transported gold nuggets during weathering and erosion. Thus, a very specific geochemical fingerprint of gold was created, which in this case, precisely matches the gold on the Nebra Sky Disk.

As for what led the Bronze Age people to specifically extract, trade, and use this gold from Cornwall, we can only speculate so far. It could be related to early tin extraction for bronze production. Meanwhile, it has been Diskovered that the gold from Cornwall was also used in Ireland during the Bronze Age, even though sufficient local natural Irish gold was available (Standish et al. 2015).

Perhaps the "golden rivers" of Cornwall already in the Bronze Age contributed to the development of a "brand awareness" and "brand loyalty" – in a time when Europe was already much more closely connected through long-distance trade of metals such as gold, tin, and copper than previously suspected.