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148 Valente & Gomes / Journal of Iberian Geology 33 (2) 2007: XXX-YYY 1. Introduction From an ecological point of view, the acid mine drainage (AMD) sites are extreme environments because impose stress on the majority of organisms. Very low pH values (pH
Valente & Gomes / Journal of Iberian Geology 33 (2) 2007: XXX-YYY 149 Mine Ore deposit Properties of the mine wastes Valdarcas Carris Adoria Cerquido Skarn with sulphides (tungsten mineralization) Quartz veins in granite (tungsten and molybdenum mineralization) Quartz veins in granite and metassedimentary rocks (tin and tungsten mineralization) Quartz veins in shear zone (tungsten, zinc and gold mineralization). Fine tails from milling and hydrogravitic separation; abundant sulphides (pyrrhotite, pyrite, arsenopyrite), carbonates (calcite and siderite), phosphates (apatite) and calcium silicate minerals Fine sulphide-rich residues from ore beneficiation; pyrite, arsenopyrite and molybdenite are the most abundant sulphides Coarse grain size residues; there is a dominance of sulphide assemblages with arsenopyrite, pyrite and galena Rough fragments resulted from crushing; the mineralogical assemblages are rich in quartz and sulphides (arsenopyrite, pyrite, chalcopyrite, sphalerite and galena) Table 1. Properties of sulphide-rich wastes in relation with the genetic type of ore deposit. Tabla 1. Propiedades de los estériles ricos en sulfuros relacionados con los distintos tipos genéticos de depósitos minerales. modifications in aquatic environments. These interactions may yield to biomineralization processes. Although biomineralization is broadly documented, references to such a process involving acidophilic algae in AMD are much rarer (Mann et al., 1987; Brake et al. 2001b, 2002). These articles report the contribution of Euglenophyta to the formation of iron-rich minerals. Besides their role promoting mineral precipitation, algae can interfere with geochemical cycles in several ways. Extra-cellular metal adsorption is known as a common strategy to limit access of toxic elements to the interior of the cells and, in such a way, to survive in stressful conditions (Gaur and Rai, 2001). As a result, algae may control acidity and metals in solution leading to natural attenuation of the AMD environmental impact (Lawrence et al., 1998; Elbaz-Poulichet et al., 2000; Valente, 2002; Casiot et al., 2004). The roles of acidophilic algae in acid mine drainage are pointed out in this paper through the characterization of acidic effluents from four abandoned mines in Northern Portugal: Valdarcas, Adoria, Carris and Cerquido (Fig. 1). Combination of ecological, geochemical and mineralogical data from those effluents provides evidence of the importance of acidophilic algal colonization for environmental monitoring and impact qualification procedures in AMD sites. 2. Methods 2.1. Selection of mining sites them possess abandoned waste-dumps with sulphides exposed to weathering processes generating AMD. The paragenesis of mining wastes is the main distinguishing factor among the sites, namely sulphide species and respective mineral proportions are different (Table 1). Besides mineralogy, inherited from primary ore, grain size resulting from ore processing are important distinguishing features. 2.2. Water sampling The sampling scheme used for effluent monitoring was optimised for each mining site, taking into consideration the main source of acid mine drainage, the heterogeneity of the effluents and the hydrologic regime. Valdarcas is the only site with permanent drainage, which allowed a more frequent sampling (monthly between 2000 and 2002). At Carris, Adoria and Cerquido superficial drainage has an ephemeral nature and therefore three sampling campaigns were performed (in the autumn of 1999, 2001 and 2002). Fig. 2 presents the location of sampling stations at Valdarcas, Carris and Adoria. At Cerquido, the absence of drainage did not allow the establishment of a fixed scheme. Therefore sampling during rainy periods took place in the main gallery entrance and in the wastedump surrounding runoff. Samples of unpolluted superficial regional waters were seasonality collected in order to describe background characteristics. The studied mining sites were selected because they represent different genetic types of ore deposits. All of
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constitucionais (Tabela 1) - e, de
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Para a implementação, a nível na
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Figura 3 - Representação esquemá
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REFERÊNCIAS Alfama V., Gomes A.M.,
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30º Curso de Actualização de Pro
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Tabela 1. Tamanho do grão em rocha
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aos alunos uma reflexão sobre mine
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Figura 4. Classificação de Streke
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das rochas, afim de deduzir qual a
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3. ROCHAS METAMÓRFICAS As rochas m
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Figura 11. Relação entre o tipo d
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sempre a determinação do tipo de
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Para relacionar o grau crescente de
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Rochas detríticas As rochas detrí
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Tabela 14: Componentes dos calcári
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Geomorfologia e Património Geomorf
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Fig. 2 - Enquadramento do litoral d
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Norte Foz do Lima Microgeoformas al
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Fig. 4 - Geossítios do Forte do C
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algumas pias de forma lobada e late
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perfeita. Acima da Estrada Nacional
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Geossítio do Monte do Galeão - Vi
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na encosta atlântica, a 85 metros;
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Fig. 19a- MDT de declives do concel
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terão sofrido soerguimento Alpino
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Fig. 22 - Soerguimento relativo dos
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tenha sido pouco intenso ou que a e
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Fig. 26 - Afloramento de geoformas
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Fig. 29 - Enquadramento estrutural
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ALVES, A.; 1996. Causas e processos
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