XII CONGRESO NACIONAL Y XI IBÉRICO DE GEOQUÍMICA Investigar los recursos cuidando el ambiente Linares (Jaén), 26 a 28 septiembre 2017 114 RELATIONSHIPS BETWEEN PHYSICO-CHEMICAL INDICATORS OF ACID MINE DRAINAGE Gomes, Patrícia a , Valente, Teresa b , Grande, José António c , Cordeiro, Mayara d a Institute of Earth Sciences (ICT), Pole of University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal, email: fpssgomes@gmail.com b Institute of Earth Sciences (ICT), Pole of University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal, email: teresav@dct.uminho.pt c University of Huelva & Escuela Técnica Superior de Ingeniería, Spain, email: grangil@uhu.es d Institute of Earth Sciences (ICT), Pole of University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal, email: mayaratcordeiro@gmail.com ABSTRACT Acid mine drainage (AMD) is an important focus of environment impact that supports the degradation of the ecosystems at global levels. São Domingos mine is a paradigmatic site in the Portuguese Iberian Pyrite Belt, known by strong contamination by AMD. The acidic waters drain into the Chança water dam, highlighting the importance of the mine regarding accomplishment of water quality compatible with human consumption. The present study shows the variations between pH, Electrical Conductivity, Total Acidity and Sulphates in the rainy season (from October to March 2017) in the most affected areas, as well as the response of the receiving water dam to the changes induced by AMD. The results indicated that the extreme values occur in one peculiar small dam (PAT 7), as result of AMD potential of the accumulations of very fine grain sulfide-rich wastes that drain into this dam. Here, strong reactivity is marked by water physical-chemical parameters as well as by the presence of mineralogical indicators, such as salt efflorescences. The correlation between parameters reflects water-mineral interactions involving the sulfides, which oxidative dissolution is responsible for the production of acid sulphate waters. Key words: physical-chemical, total acidity, sulphates, acid mine drainage, São Domingos mine. 1. INTRODUCTION Since pre-historic times, the humankind explores natural resour- ces to obtain raw materials. The exploitation of mineral resour- ces stimulates the economy, creates wealth, but generates impacts that may be the basis of some conflicts of interest with other uses of the territory. The mining industry is one of the most problematic activities in the primary sector. This impact is even superior in mines whose abandonment occurred in an uncontro- lled manner, generating environmental focus that persists until today (Gomes, 2011). Sulfide-rich waste-dumps, when exposed to weathering proces- ses, promote a global environmental problem related with acid mine drainage (AMD) (Chockalingam and Subramaniam, 2009). In the rainy season, waters interact with sulfide materials in the waste-dumps and release acidity, sulphate and metals, forming acid sulphate-rich leachates (Grande et al., 2016). In the Iberian Pyrite Belt (IPB) there are many abandoned mines that do not present any corrective or preventive measures for the aquatic system. São Domingos mine is located in the Portuguese sector of the IPB, and it was an important mining centre dating back to pre-Roman times remaining in activity until 1966, when it was definitely halted (Álvarez-Valero et al., 2008). It is characterized by an open pit exploitation of massive sulfide ores that are located near the top of the Volcanic Sedimentary Complex. Nowadays, the waste-dumps are spread along appro- ximately 5.5 km in the margin of the Chança River, being the main contaminant focus of the water system. Inserted in the semi-arid climate of this area and considering the lack of water resources in this region (Alentejo), the study of AMD contamina- tion is a relevant issue. The specific objectives of the present work are focused on cha- racterizing the variations between pH, Electrical Conductivity, Total Acidity and Sulphates in the rainy season (from October to March) and observing the response of the aquatic system to the changes induced by AMD. This will give indication about the de- gree of contamination in São Domingos and will allow prelimi- nary understanding of the hydrochemical and hydrological relationships that are occurring in the receiving aquatic system (Chança reservoir, used human consumption). Sampling points were selected immediately upstream and downstream of São Domingos mine, in order to evaluate the effects of the leachates on the physical-chemical parameters of the system. 2. MATERIALS Field sampling and laboratory analyses implied the use of diverse equipment, materials and reagents. Multiparameter portable meter CRISON MM40+ was used for in situ parameters. The follo- wing Orion probes were used: combined pH/ATC electrode Triode ref. 91-07WM and a conductivity cell DuraProbe ref. 013010. Potential redox (Eh) was measured using multiparameter porta-