Legacy of sulfide ore mining in the Friuli Venezia Giulia region: geochemical behaviour of potentially toxic trace elements and their impact on environmental compartments.

In the recent decades, we are witnessing an increasing demand for natural resources, driven by demographic and technological development, and now also for the energy and digital transition. This need translates into more increased extraction and production of larger volumes of resources from the Earth, where the mining industry is already active. Yet, in those countries where the mining industry has been stopped, interest is growing. However, although past, present, and future mining activity is always indispensable, it is never free from potential long-lasting environmental issues or disasters and conflicts with the populations living around the mining sites. The contamination of the environment from the mining activity is a geochemical issue. Geochemical research at mining sites allows to assess the environmental impact of mining activities on the surrounding ecosystem and human health as well as to understand the mechanisms of release, attenuation and in general partitioning between different environmental compartments of potentially toxic elements (PTEs) and other contaminants. The occurrence of PTEs in the environment due to the presence of the mining activity is a well-known issue. However, only the behaviour of the most common elements has been extensively studied, e.g., zinc (Zn), lead (Pb), arsenic (As). In contrast, less common but equally potentially dangerous elements, such as thallium (Tl), received less attention. Thallium is an emerging natural or anthropogenic contaminant due to its potential toxicity to ecosystems and human beings, which is also often disregarded by national regulations. In freshwaters, Tl is highly mobile and toxic at very low concentrations ranging from a few μg/L to mg/L. The present doctoral thesis aims to study the environmental legacy of regional mining sites (Friuli Venezia Giulia, Italy), now closed for more than 30 years. The two selected mines are relevant from an environmental, historical or political point of view. For example, the Raibl mine is currently under reclamation due to problems of cross-border contamination issues of potentially toxic elements (PTEs), among which major concerns are about high concentrations of Tl in the riverine waters. In contrast, other less important sites such as the Cu-Sb(-Ag) Monte Avanza mine, nowadays are completely abandoned. Hence, since environmental issues are different among different types of ore deposits and adopted processing systems, the objectives of this PhD thesis, through two case studies (Pb-Zn carbonate-hosted mine, and a Cu-Sb(-Ag) fahlore mine), are: 1) To reconstruct the history of the mining sites, focusing on the interactions between mining and the environment 2) Evaluating analytical methods for geochemical and contamination assessments. 3) To evaluate the impact of mining in the two main mines of FVG by potentially toxic trace elements in different environmental matrices (water, soils, mining waste, atmosphere) 4) To study the distribution, the temporal variations and the behaviour of thallium and other PTEs with focus on geochemical similarities and differences in several environmental compartments of sites affected by the mining activity. Particular attention was given to the release and natural attenuation processes of PTEs. Making a step for creating or improving geoenvironmental models (i.e., models used to predict the effects on the environment characteristics for different ore types) for carbonate-hosted Pb-Zn and Cu-Sb fahlore mining sites.