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Slags as Evidence for Copper Mining above Casaccia, Val Bregaglia (Central Alps)

1
Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA
2
School of Urban Planning and Municipal Engineering, Xi’an Polytechnic University, Xi’an 710048, China
3
Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA
4
Independent Researcher, 7602 Casaccia GR, Switzerland
5
Independent Researcher, 7610 Soglio GR, Switzerland
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(5), 292; https://doi.org/10.3390/min9050292
Received: 4 March 2019 / Revised: 7 May 2019 / Accepted: 8 May 2019 / Published: 12 May 2019
(This article belongs to the Special Issue Metallurgical Slags)
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Abstract

Slags from the remote Mota Farun locality above Casaccia (Val Bregaglia, Swiss Alps) have been analyzed with scanning electron microscopy, X-ray powder diffraction and microfocus synchrotron X-ray diffraction to determine mineralogical composition and microstructures. Non-magnetic slag samples are largely composed of euhedral and dendritic iron-rich olivine in a glassy matrix. Locally there are zones with globular inclusions rich in bornite ((Cu5Fe)S4) and locally metallic copper. Some regions display dendritic pentlandite ((Fe,Ni)9S8). Magnetic samples are mainly composed of fayalite (Fe2SiO4) and wüstite (FeO), with minor magnetite (Fe3O4). The mineralogical composition indicates that slags were the product of copper smelting. The slag compositions and morphologies are analogous to slags described from the Oberhalbstein (Graubünden, Switzerland) and the Trentino Alps (Italy) which are attributed to metallurgical exploitations of the Late Bronze Age. While the origin of the ore could not be determined, it may be related to ore deposits of chalcopyrite in greenschists and serpentinites in the vicinity, such as Alp Tgavretga (Septimer Pass) and Val Perossa (Val Bregaglia). View Full-Text
Keywords: copper smelting; slags; Swiss alps; Casaccia; scanning electron microscopy; synchrotron X-rays copper smelting; slags; Swiss alps; Casaccia; scanning electron microscopy; synchrotron X-rays
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Wenk, H.-R.; Yu, R.; Tamura, N.; Bischoff, D.; Hunkeler, W. Slags as Evidence for Copper Mining above Casaccia, Val Bregaglia (Central Alps). Minerals 2019, 9, 292.

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