The present study focuses on the physical, mineralogical and geochemical characterization of the tailings pond from Straja Valley, resulted from the now abandoned ore-processing plant of Tarnița (Ostra). In terms of granulometry, around 70% of waste material consists of fine and very fine particles. The sulfides of the waste are pyrite, subordonate sphalerite and very rare galena. The silicates consist mainly of quartz and sericite, subordinate chlorite, feldspars; accidentally, also barite was identified within the waste. The salt crusts occur on some areas of the surface of the tailings pond. They consist mainly of mineral species of the alunite-jarosite solid solution series (i.e., jarosite, hydronium jarosite, plumbojarosite and alunite). However, small amounts of gypsum (detected significant only in white crust) and copiapite were also identified, as well as clay minerals (i.e., kaolinite and illite), formed through the weathering of silicates. All samples from the beach and dam of the tailings pond display a high acidity (pH mean of 2.81) and relative high amounts of water soluble fraction (mean of 9.71 wt%). The most abundant major elements are Si, Fe and Al; the decreasing sequence of abundance is the following: Si>Fe>Al>K>Mg>Na>Mn. The most abundant minor elements are Pb, Zn, Cu and As, whom sequence of abundance is Pb>Zn>Cu>As>Cr>Co>Cd. According to the particle size of the waste, some of elements (e.g. Fe, Mn, Cu, Zn, As) have a high affinity for the fine and very fine particles, being rather concentrated in the silt and clay fractions than within the arenite fractions. Multivariate statistics revealed four distinct types of waste, as well as three factors that control the distribution of the chemical elements: 1) water soluble fraction, 2) pyrite abundance; 3) Ca-bearing minerals. Moreover, the rainfall regime and morphology of the waste deposit also seem to influence the mobility and accumulation of both major and minor elements on the surface of the tailings pond. In terms of environmental pollution, the fine and very fine particles, which accumulate very high amounts of minor and major elements, are susceptible to be transported towards the surrounding areas by wind or water, during rainfall. During the latter events, the acidic leachates, highly enriched in toxic elements, were mobilized by runoff, thus reaching the neighborhoods of the waste deposit.