The Neolithic variscite mines of Gavà, Catalonia : Criteria for mineral exploration and exploitation in the Prehistory
Díaz-Acha, Yael (Museu de Ciències Naturals de Barcelona)
Campeny, Marc (Museu de Ciències Naturals de Barcelona)
Melgarejo, Joan Carles (Universitat de Barcelona. Departament de Mineralogia, Petrologia i Geologia Aplicada)
Andreazini, Aleu (Universitat de Barcelona. Departament de Mineralogia, Petrologia i Geologia Aplicada)
Pastor, Míriam (Universitat de Barcelona. Departament de Mineralogia, Petrologia i Geologia Aplicada)
Pujol-Solà, Núria (Universitat de Barcelona. Departament de Mineralogia, Petrologia i Geologia Aplicada)
Proenza, Joaquín A. (Universitat de Barcelona. Departament de Mineralogia, Petrologia i Geologia Aplicada)
Bosch Argilagós, Josep (Museu de Gavà)
Torró i Abat, Lisard (Universitat Autònoma de Barcelona. Departament de Geologia)
Villanova-de-Benavent, Cristina (School of Environment and Technology. University of Brighton)
Castillo-Oliver, Montgarri (Mac-quarie University. Department of Earth and Planetary Sciences)
Lehbib, Saleh (Ministery of Water and the Environment. Sahrawi Arab Democratic Republic)
Camprubí, Antoni (Universidad Nacional Autónoma de México. Instituto de Geología)

Date:	2019
Abstract:	The Gavà Neolithic Mining Complex (GNMC) located in Catalonia was devoted to the exploitation of green variscite used in the crafting of ornaments. Archaeological works in more than 100 mines indicated that this mining activity was carried out ~5800 years before present. GNMC constitutes (1) one of the earliest known examples of underground mining in Europe, (2) the earliest example of large-scale mining for ornamental use, and (C) the earliest of the application of complex geological and mining concepts. In the GNMC variscite is found as two distinct styles: (1) replacement of thin fluorapatite beds, which are interbedded with pyritic organic-rich black shales of Silurian age; and (2) veinlets crosscutting these materials. This set of geological materials is unconformably covered locally by Quaternary calcretes. Variscite formed as a result of Quaternary supergene processes, which oxidized the pyrite and produced acidic, oxidized solutions. The resulting fluids mobilized phosphate from apatite and leached Al and organic matter out of Silurian shales, thus leading to the precipitation of the Al-rich phosphates as vein infillings and strata-bound replacements after apatite. The formation of variscite is restricted to the extent of the oxidizing front, and variscite of both mineralization styles changes in color from yellowish green near the surface to deep green in depth. The study area contains two mining fields: Can Tintorer and Can Badosa-Les Ferreres range. The presence of abundant subvertical variscite veins in Can Tintorer allowed a complex development of galleries at different exploitation levels communicated by shafts and ramps, achieving 15 meters depth. The exploitation by Neolithic miners was by overhand and underhand stoping; they also used pillars and refilling of older exploitations to avoid the mine collapsing. These mines were opened in many cases by shafts that were dug directly through hard Quaternary calcretes, favoring the galleries' stability and revealing that miners understood that mineralization continues underneath the calcrete cover. Geological mapping reveals that exploitations in the Can Badosa-Les Ferreres area are simple, showing a single entrance to simple galleries or ramps attaining less than 5 m in depth and directly excavated on phosphate outcrops. Contrastingly, the mines in the Can Tintorer area have several entrances that consist of vertical shafts through a Quaternary cover, presenting an intricate geometry with many large and communicated galleries at different depths with a system of cameras and pillars. Although the development of both mining areas was essentially contemporaneous, the Can Badosa-Les Ferreres area can only be considered an exploration area. In addition, mining was carried out on minerals adjacent to variscite, not directly on variscite veins themselves, thus indicating that the miners were effectively using a wealth of geological knowledge that was previously acquired in the complex operations in the Can Tintorer mines.
Grants:	Agència de Gestió d'Ajuts Universitaris i de Recerca 2014/SGR-100820
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, sempre que no sigui amb finalitats comercials, i sempre que es reconegui l'autoria de l'obra original.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Variscite ; Veinlets ; Replacement ; Supergene ; Quaternary ; Stoping ; Neolithic ; Mine ; Protohistoric mining
Published in:	Boletin de la Sociedad Geologica Mexicana, Vol. 71, Núm. 2 (2019) , p. 295-319, ISSN 1405-3322

DOI: 10.18268/BSGM2019v71n2a5

25 p, 7.6 MB

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