Mineral Inventory of the Algares 30-Level Adit, Aljustrel Mine, Iberian Pyrite Belt, Portugal

Abstract

Mining activity in Algares (Aljustrel Mine, Portuguese sector of the Iberian Pyrite Belt, IPB) stems prior to Roman times. As the orebody is vertical and relatively thin, mining was carried out mainly along underground adits (galleries). Nowadays, the deposit is considered exhausted and the area is being rehabilitated for a different use. The Algares +30 level adit intersects two volcanic units of the IPB Volcano-Sedimentary Complex. The massive sulphide and related stockwork zone are hosted by the Mine Tuff volcanic unit and are exposed in the walls of the gallery, showing intense hydrothermal alteration. Along the mine adit, the geological sequence is affected by strong oxidation and supergene alteration, giving rise to the formation of secondary minerals through the oxidation of the sulphides. The most common minerals found were melanterite (FeSO4·7H2O) and chalcanthite (CuSO4·5H2O), forming essentially massive or crystalline aggregates, ranging from greenish to bluish colours. Melanterite from the walls revealed to be Cu-rich by opposition to that from stalactites/stalagmites formed below the old ore storage silo revealing the low-copper-grade ores exploited underground. The mineralogy of the efflorescent salts was used to ascertain the processes involved in their formation, and moreover, the inventory of minerals is presented, as well as their principal characteristics.

Assessment of the Environmental Impact of Acid Mine Drainage on Surface Water, Stream Sediments, and Macrophytes Using a Battery of Chemical and Ecotoxicological Indicators

“…The results reported in this study, and in other studies that have assessed the environmental impact in the Aljustrel mining area [2][3][4]9,22,23] can be used to evaluate the benefits of the remediation measures at the site, documenting the "ground zero" situation. Unfortunately, remediation measures are not always effective to counterbalance years of AMD impact, and, for instance, some remediation actions took by the regional Government of Andaluzia in the Spanish part of the IPB, both active and passive, have been revealed as highly ineffective for reducing the environmental impact of AMD waters, due to chemical and climatic constraints [17].…”

“…It represents an important metallogenetic province of volcanic-hosted massive sulfide deposits, one of the world's most important [3,9,10]. These massive sulfide deposits are mainly constituted by pyrite (FeS 2 ), the dominant ore (>90%) [4], and variable amounts of sphalerite ((Zn,Fe)S), galena (PbS), and chalcopyrite (CuFeS 2 ). Other minerals, such as arsenopyrite (FeAsS), are less representative, while silver (Ag) and gold (Au) are important subproducts (Aljustrel's geological setting was extensively described by, e.g., [3][4][5]9,22,23]).…”

“…These massive sulfide deposits are mainly constituted by pyrite (FeS 2 ), the dominant ore (>90%) [4], and variable amounts of sphalerite ((Zn,Fe)S), galena (PbS), and chalcopyrite (CuFeS 2 ). Other minerals, such as arsenopyrite (FeAsS), are less representative, while silver (Ag) and gold (Au) are important subproducts (Aljustrel's geological setting was extensively described by, e.g., [3][4][5]9,22,23]). The extraction of pyrite has been mainly responsible for the pollution observed in soils, tailings, superficial water, and sediments [1].…”

“…The extraction of pyrite has been mainly responsible for the pollution observed in soils, tailings, superficial water, and sediments [1]. After a period of interruption in the mining works, exploration was reestablished in 2009 by the company ALMINA-Minas do Alentejo, S.A., using the best available technologies and environmental practices, and the above-described mine-activity-affected areas begun to be rehabilitated by EDM, the state company which is responsible for the environmental liabilities in mine areas [4,9]. Samples of water, sediment, and the aerial part of a macrophyte (Scirpus holoschoenus L.) were collected from three sampling sites in the Água Forte stream (Figure 3), approximately 10 km long (Site 1, 37 • 1).…”

“…The Aljustrel mining area (Portugal), located in the SW sector of the Iberian Pyrite Belt (IPB), constitutes one paradigmatic example of this reality [1][2][3]. The exploitation started before the Roman occupation of the Iberian Peninsula [4], evident by the vestiges of intense mining activity which were found together with the Roman spoils [5] and was one of the most important mining explorations during that period. The intensive mining activity started again in 1849, with the concession being given to different foreign and national companies over the years, for example, Transtagana [6], Societé Anonyme Belge des Mines d'Aljustrel [7], Pirites Alentejanas S.A., and more recently, Almina, Minas do Alentejo S.A. During its intense exploitation, which took place during the twentieth century, the pyrite at Aljustrel was processed by a wet treatment, which began by the roasting or calcination of the ore, in which the copper sulfide was transformed into copper sulphate, followed by the dissolution of the sulphate in water.…”