Environmental study of Reps sulfide mine dumps, Mirdita District, Northern Albania

The mine and processing site of Reps operated until 1994 in the Fan valley, about 20km NE of Rreshen, Northern Albania. The mine dumps host sulfide-rich tailing materials resulting from the copper concentration processes. These tailing dumps are issues of environmental concern because of their proximity to the river, the presence of acid drainageproducing minerals and the unstable conditions of the piles. The aim of this work is to evaluate the release of potentially toxic elements (PTE) in the local environment through a geochemical survey of the two main piles, respectively named Reps1 and Reps2. We collected 46 solid samples and 17 water samples representative of the upstream flow, drainage and downstream delivery. Analyses have been conducted in order to characterize (i) the mineralogy, grain size and bulk chemical composition of the earthen samples; (ii) the concentration of PTE either in solid materials and waters; (iii) the presence and persistence of acid drainage. The features of the earthen materials have been defined by grain size and bulk elemental (ICP) composition, pH measures and in situ permeability tests. Microscopy, XRD and MPA analyses have also been performed on selected samples. The mineralogical and geochemical analyses have been performed on the granulometric fraction <2mm. The physical and chemical parameters of the water samples have been investigated through pH-Eh measurements and atomic emission spectrometry. The acid drainage production and the neutralising capacity were evaluated for a set of samples through the Acid Base Account (ABA) test. Moreover, we assessed the spatial relations between the geochemical variables using dedicated mapping softwares. The comparison between the pH analyses on solid samples reveals a stronger acidity of the waste materials of the Reps2 dump (pH=2.4-3.7), with respect to Reps1 (pH=3.2-4.3). Such a difference is due to a higher content of sulfides in the Reps2 samples. These contain a mixture of pyrite, marcasite, minor chalcopyrite, sphalerite and enargite, with associated silicates, oxides (Fe and Fe-Mg spinels) and sulphates (gypsum, barite). Secondary phases comprise hydrated Fe-sulfates and hydroxides. The mineralogical composition of these samples is reflected in the average concentration of S (14.9%) and hazardous metals such as Cu (4430 ppm), Zn (1970 ppm), and As (660 ppm). The drainage water samples show very low pH values (2.3-2.7), with respect to the upstream waters (pH=6.7-7.8). This acid character is associated to a high concentration of ions, the highest values being those of Zn (up to 100 ppm), Cu (up to 20 ppm) and Mn (up to 20 ppm). Our preliminary results on the potential acid drainage production include a total H2SO4 release of 588.087t and a predicted buffering time of 230 000 years. Our investigations at Reps show that this site undergoes a general widespread pollution due to the storage of sulfur and PTE-rich fine grained material in strong disequilibrium with the local morphology and adjacent to a main river that works as a collector of highly acid PTE-rich phases drainage water.