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Abstract:

The tailings of Straja Valley waste deposit consist mainly of minerals resulting from the metallic ores and their host schist of Lesu Ursului mining field (primary minerals). Additionally, secondary minerals produced through the weathering of the first ones were identified (Na- and Pb-jarosite, Mg-copiapite, gypsum, alunite, apjohnite, and goethite). Two grain-size classes were separated namely coarse grains (CG) (size larger than 0.25 mm) and fine grains (FG). The descriptive statistic data showed that the geochemical properties of the waste depend on its location on the tailings pond, abundance of the soluble fraction (in close relation with secondary hydrated sulfates) and, to a lesser extent, the waste grain size. Principal Component Analysis (PCA) carried out on geochemical data revealed the following patterns of waste: (i) pyrite-rich tailings from the waste beach are frequently fine-grained and have a higher Cu content; (ii) while the coarse-grained waste is rich in silicates, it also contains secondary minerals that trap Pb (Na-jarosite, Pb-jarosite, gypsum); (iii) if the silicate-rich tailings are controlled by quartz, they are coarse-grained and depleted in secondary minerals; (iv) the fine-grained silicate-rich waste also contains secondary minerals (e.g., Na-jarosite, Mg-copiapite, gypsum, alunite, and clay minerals) that collect Pb, Al, Mg, Ca, and Na in their structure. The environmental risks related to wind-driven transport of waste during long drought periods can be presumed as following: (i) mechanical pollution with quartz and chemical pollution with Pb, Zn, Cd trapped in sphalerite ± galena, Pb-jarosite, Mg-copiapite, goethite, apjohnite, and clay minerals, when wind exceeds 7.3 m/s; (ii) pollution with fine-grained pyrite (and Cu, Zn, Cd within) or secondary minerals that accumulate Pb and As (Pb-jarosite, Mg-copiapite, apjohnite, and goethite), when the wind speed is less than 7.9 m/s.