This paper describes the occurrences, the mineralogical assemblages and the environmental relevance of the AMD-precipitates from the abandoned mine of Valdarcas, Northern Portugal. At this mining site, these precipitates are particularly related with the chemical speciation of iron, which is in according to the abundance of mine wastes enriched in pyrrhotite and pyrite. The more relevant supergene mineralogical assemblages include the following environmental minerals: soluble metal-salts, mainly sulphates, revealing seasonal behaviour, iron-hydroxysulphates and iron-oxyhydroxides, both forming ochre precipitates of poorly and well-crystalline minerals. Pollution potential of the most highly water soluble salts was analysed in order to evaluate the environmental effect of their dissolution by rainfall. Laboratory experiments, carried out with iron and aluminium sulphates, demonstrated the facility to release metals, sulphate and acidity upon dissolution. Regarding the ochre precipitates, composed by several less soluble iron (III)-minerals, the spatial distribution on the nearby aqueous system as well as the proportion of Jarosite, Schwertmannite and Goethite in the mixtures gave information about the halo's contamination promoted by the AMD emerging from the waste-dumps.

Fuzzy logic was applied to model acid mine drainage (AMD) and to obtain a classification index of the environmental impact in a contaminated riverine system. The data set used to develop this fuzzy model (a fuzzy classifier) concerns to an abandoned mine in Northern Portugal-Valdarcas mining site. Here, distinctive drainage environments (spatial patterns) can be observed based on the acid mine drainage formed in the sulphide-rich waste-dumps. Such environments were established, as the effluent flows through the mining area, using several kinds of indicators. These are physical-chemical, ecological and mineralogical parameters, being expressed in a quantitative or qualitative basis. The fuzzy classifier proposed in this paper is a min-max fuzzy inference system, representing the spatial behaviour of those indicators, using the AMD environments as patterns. As they represent different levels (classes) of contamination, the fuzzy classifier can be used as a tool, allowing a more reasonable approach, compared with classical models, to characterize the environmental impact caused by AMD. In a general way it can be applied to other sites where sulphide-rich waste-dumps are promoting the pollution of superficial water through the generation of AMD.

The Carris orebody consists of two partially exploited W-Mo-Sn quartz veins formed during successive shear stages and multipulse fluid fillings. They cut the Variscan post-D3 Gerês Itype granite. The most important ore minerals are wolframite, scheelite, molybdenite and cassiterite. There are two generations of wolframite. The earlier generation of wolframite is rare and has the highest WO 4 Mn content (91 mol%) and the most common wolframite contains 26-57 mol% WO 4 Mn. Re-Os dating of molybdenite from the ore quartz veins and surrounding granite yield ages of 279 ±1.2 Ma and 280.3±1.2 Ma, respectively which are in very good agreement with the previous ID-TIMS U-Pb zircon age for the Carris granite (280±5 Ma). The fluid inclusion studies on quartz intergrown with wolframite and scheelite, beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit. The first was a low to medium salinity aqueous carbonic fluid (CO 2 between 4-14 mol%) with less than 1.95 mol% N 2 , which was only found in quartz associated with wolframite. The other was a low salinity aqueous fluid found in all the four minerals. The homogenization temperatures indicate minimum entrapment temperatures of 226-310ºC (average 280ºC) for the H 2 O-CO 2 -N 2 -NaCl fluid and averages temperatures of 266ºC for scheelite and 242ºC, 190ºC and 160ºC for the last generations of beryl, fluorite and quartz, respectively. It was estimated that wolframite was deposited ~7 km depth, assuming a lithostatic pressure, probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTPrecipitation of scheelite and sulphides took place later, at the same depth, but under an hydrostatic or suprahydrostatic pressure regime, and probably caused by mixing between the magmatic-hydrothermal fluid and meteoric waters that deeply penetrated the basement during post-Variscan decompression.

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The study area is located in the Central Iberian Zone, a major tectonic unit of the Iberian Massif (Variscan belt). In this region the basement is composed of Cambrian-Ordovician sedimentary and minor volcanic rocks that underwent deformation and metamorphism during the Carboniferous. These metamorphic rocks host ca. 331-308 Ma granitic plutons emplaced during the D 2 extensional and D 3-D 4 contractional deformation phases. The gold-bearing quartz veins from the Santo António mine (Penedono region) occur in granite formed at 310.1 ± 1.1 Ma and postdated the peak of metamorphism. Gold-silver alloy is included in quartz, but mainly occurs in spaces between grains or micro-fractures within arsenopyrite of all three generations and less in pyrite. Late sulphides and sulphosalts were deposited along fractures mainly in arsenopyrite, and locally surrounding the gold-silver alloy grains. Ferberite, scheelite and stolzite replace arsenopyrite. The abundant aqueous carbonic fluids and the occurrence of a low-salinity fluid and their minimum possible entrapment temperature of 360-380 °C suggest that this gold-forming event began during the waning stages of the Variscan orogeny. The mean δ 34 S values of arsenopyrite and pyrite are − 4.7‰ and − 3.8‰, respectively. HeAr -Ne isotopic data suggest a crustal origin. The ascent of the granite magma has provided the heat for remobilization of gold, other metals and metalloids from the metamorphic rocks. This gold-arsenopyrite deposit has thus similar characteristics as other selected gold-arsenopyrite deposits from the Iberian Massif, but it contains tungstates.