Fare rame: quadro di sintesi su siti e strutture produttive della metallurgia primaria protostorica del Trentino

Bellintani, Paolo; Silvestri, Elena; Bassetti, Michele; Cappellozza, Nicola; Degasperi, Nicola; Nicolis, Franco; Pagan, Nicola; Pearce, Mark

Abstract

198 “smelting sites”, dedicated to the processing of copper minerals (mixed sulphides mostly with chalcopyrite) are recorded in eastern Trentino. In general, they are located at altitudes of between 1000 and 1800 m a.s.l.. They are traditionally dated to the Late Bronze Age.
Most of our knowledge regarding the later prehistoric ore processing on the southern slopes of the central-eastern Alps comes from the smelting site of Acqua Fredda at the Redebus pass. The site was discovered in 1979 and investigated in the 1980s and 1990s, in the course of a collaborative research project involving both the Archaeological Heritage Office of the Autonomous Province of Trento and the Deutsches Bergbau-Museum Bochum. Since the early 2000s, the Trento Archaeological Heritage Office has intensified the systematic mapping and protection of these particular sites. Whenever necessary, endangered contexts were investigated by means of excavation and archaeometric
analyses.
In Trentino, the main copper ore deposits are found in a large swathe of territory to the east of Trento. Its western boundary runs from Mount Calisio (in the north) to Mount Marzola (in the south), while to the east it includes the southernmost part of the Pinè plateau, the Mocheni Valley and the Upper Valsugana. This area roughly coincides with that of the prehistoric smelting sites dating to the Late Bronze Age. They can be grouped into four macro-areas, centred on the outcropping of the metamorphic basement (the Cembra and Mocheni Valleys; the Valsugana; the Lavarone and Luserna plateaux and finally Tesino and Primiero). Up to now there is very little evidence regarding prehistoric mines and primary ore beneficiation sites, which turns the site of Vetriolo into an important point of departure.
General features
The recorded sites have many characteristics in common: proximity to ore deposits (with the important exception of the Lavarone and Luserna plateaux); the presence of water at the site or close by, and their location on flat areas, natural or artificial, on the mountain slopes. In most cases (84%) the sites were identified thanks to the presence of coarse slags. Plate slags were found at 57% of the sites, while slag sand has been recorded at a significantly lower number of sites (9%). Structures or equipment used in the smelting process have been rarely observed: only 9% show remains of pyrotechnological structures, such as pieces of furnace lining; ground stone tools such as millstones, hand stones, anvils and pounders were found on 7% of sites; only 3% have yielded technical ceramics, such as pieces of tuyères.
Structures and processing residues
Furnaces: these are most likely pyrotechnological structures intended for the processing of ore and/or derived products such as matte. In 16 cases these are stonewalled structures (generally in "porphyry"), of quadrangular shape which always and only have three sides (the fourth side must have been removable). Three structures at Acqua Fredda were defined as "Grubenofen"("hearth-pits") but most likely are the outcome of the dismantling of the stone walls of the furnaces so that only the concave base is preserved.
Complex structures and batteries: in several cases (Acqua Fredda, Fierozzo – Valcava, Luserna – Platz von Motze), complex structures, such as double furnaces and the unique battery at Acqua Fredda, consisting of 4 contiguous furnaces built into a single masonry structure, were found.
Hearths: these are pyrotechnological structures that cannot be interpreted as smelting furnaces. The "hearth" context n. 517 at Transacqua could have been used to obtain quartz sand from local metamorphic rocks, which would have been useful for the processing of copper sulphides.
Roasting beds: remains of elongated regular-shaped platforms, delimited by stones of various sizes, used for the roasting (desulphurisation) of the ore and/or intermediate products of the smelting process. In one case (Transacqua-Acquedotto del Faoro) the structure shows a bottom layer of plate slags.
Wooden structures: pointed poles, planks and large boards presumably related to structures such as roofs, canopies, fences etc. At Acqua Fredda the excavators unearthed the remains of a wooden lining of a channel that brought water from the Rio Acqua Fredda to be used in different steps of the working process. Other stake alignments, and the shape of the slope of the slag sand deposit (at Segonzano) might be indicative of gabions or walls to retain slag dumps.
Portable equipment: anvils, pounders, hand stones and grindstones. For coarser crushing, anvils were used (from 20 to 60 cm max. width); the crushing produced cup-shaped depressions on their active surfaces. For finer grinding of the crushed material, grindstones with a slightly concave and ribbed use surface were used.
Types of slag
Four types of slag have been identified: coarse slag (Schlackenkuchen); plate slag (Plattenschlacken) with a thickness of between 0.2 and 0.8 cm (or between 1 and 1.2 cm in a variant), "massive" slag with more than 1.8 cm of thickness, and "slag sand" (better defined as "ground slags" or "granulated slag", grain size 1-3 mm).
The coarse slags are not homogeneous and could be interpreted as partially liquefied material ("immature slags"); plate slags (mainly composed of fayalite) derive from a cooling of material processed above a liquid mass (matte/metal) at a temperature around 1150 - 1200° C. Slag sand is composed of small fragments of slag, and was produced by crushing the slag in order to separate and collect material to be reprocessed.
Dumps and other concentrations of waste
The dumps were located downslope of the smelting facilities. At Luserna – Platz von Motze, the dump, which has only been partially investigated, seems to consist of a large heap (over two metres of thickness) of coarse and plate slag. At the better investigated sites (Acqua Fredda and Segonzano – Peciapian) the lower part, in terms of slope, of the dump is characterized by the presence of "slag sand", with sequences of layers that, in the case of Acqua Fredda, are over
two metres thick.
Form and internal organisation of the sites
The maximum area recorded to date for a smelting site is that of Segonzano – Peciapian - Area A, which is estimated to be around 5200 m2, followed by Acqua Fredda and Fierozzo – Valcava (between 2500 and 3000 m2 approx.), Luserna – Platz von Motze (c. 1850 m2) and finally Transacqua – Pezhe Alte and Terrebis (between 1000 and 1500 m2 approx.). The size of the area may be connected to whether or not activities were repeated at the same site, that is to whether the facilities were rebuilt (partially relocated), or to differences of a functional nature (small differences in the production process). Confirmation of the multi-phase nature of the smelting sites are the layers of slags and "slag sand" that almost always cover the structures (making non-invasive investigations very difficult).
At the best documented sites (Luserna – Platz von Motze and Acqua Fredda) there are groups of four or five furnaces per phase. At Luserna – Platz von Motze the smelting facilities seem to consist of a pair of furnaces and a roasting bed, placed opposite each other, as frequently documented in the Austrian mining districts since the Middle Bronze Age. At Acqua Fredda however, there are individual furnaces (perhaps also in pairs) during the first phase of the site, while in the second phase the design was changed to a single "battery" of four furnaces embedded in a wall. Structural elements that can be attributed to washing facilities are documented at Acqua Fredda only and were used to process ground slag (in order to recover material to be resmelted), while it is probable that the ore was "beneficiated" (enriched) in the vicinity of the mines (as seems to be documented at Vetriolo).
Finally, on the basis of the findings of the field research it is not possible to state what the final product of these workshops really was. One of the important questions is, whether refining took place on site or elsewhere. On the basis of investigations of the compositional and textural characteristics of the slag it has been suggested that unrefined copper was produced.
Problems of chronology of the second phase of Trentino metallurgy
In the archaeological literature, the late prehistoric mining activity is traditionally dated to the Recent Bronze Age and phases 1 and 2 of the Final Bronze Age. However, there are currently several indications that it may have begun earlier, such as at Gardolo di Mezzo, a site consisting of a settlement, as well as a cult and funerary complex, where different types of smelting slag can be found in levels dating back to the Early and Middle Bronze Age.
The problem of filling the gap between the two phases of prehistoric smelting in the Trentino-Alto Adige region has also been raised by some of the 46 radiocarbon dates obtained from 18 smelting sites, which seem to evidence that the second phase of smelting began earlier than the Recent Bronze Age 2. Further confirmation comes from provenance studies on the origin of the copper in metal objects typologically dated to all the phases of the Italian (in particular from the Garda region) and European (Scandinavia, Serbia, Bulgaria) Bronze Age, which suggest a possible South-Alpine origin (Trentino - Alto Adige/Veneto) for the ore.
On the basis of these considerations, it is therefore possible that, for the second phase of the prehistoric exploitation of the southern Alpine deposits, a chronological framework less distant from Stöllner's model for the transalpine mining districts can be proposed. According to this model, the new mining technology, which originated around the large chalcopyrite deposits of the Mitterberg, entailed the development of new facilities, in particular quadrangular masonry furnaces, frequently in pairs. The development of the new mining and unrefined copper production technology has a first peak between the 16th and the 13th century BC (Bz C/D), followed by a decline around the 12th century BC (Ha A1), with a second peak in Tyrol between the 11th and 10th century BC (Ha A2/B1) and finally ends between the 9th and 7th century BC. The peak of mining and smelting activity in Trentino would seem to be between Recent Bronze Age 2 and Final Bronze Age 1/2, i.e. in contemporary with the development of the Luco/Laugen A facies, while it is only on the basis of some radiocarbon dates that the end of prehistoric smelting in the Trentino may be placed around the 9th century BC.

Citation

Bellintani, P., Silvestri, E., Bassetti, M., Cappellozza, N., Degasperi, N., Nicolis, F., …Pearce, M. (2021). Fare rame: quadro di sintesi su siti e strutture produttive della metallurgia primaria protostorica del Trentino. In P. Bellintani, & E. Silvestri (Eds.), Fare Rame: La metallurgia primaria della tarda età del Bronzo in Trentino: nuovi scavi e stato dell’arte della ricerca sul campo (269-326). Provincia autonoma di Trento

• Acceptance Date: Sep 4, 2021
• Online Publication Date: Oct 17, 2021
• Publication Date: Sep 24, 2021
• Deposit Date: Oct 6, 2021
• Publicly Available Date: Sep 25, 2022
• Publisher: Provincia autonoma di Trento
• Pages: 269-326
• Book Title: Fare Rame: La metallurgia primaria della tarda età del Bronzo in Trentino: nuovi scavi e stato dell’arte della ricerca sul campo
• ISBN: 9788877025067
• Keywords: smelting sites; pyrotechnological structures; Bronze Age; Early Iron Age
• Public URL: https://nottingham-repository.worktribe.com/output/6394109
• Publisher URL: https://www.cultura.trentino.it/Pubblicazioni/Fare-Rame