Decommissioned mining areas: an environmental issue or a source of critical raw materials? Insights from the Pb-Zn Raibl mining district (northeastern Italian Alps)

The demand for natural mineral resources has been rising in recent decades due to changes in the energy, ecological and digital disciplines. This requires a greater demand for extraction and production of critical raw materials (CRMs). Among the CRMs, the occurrence of metal(loid)s including potentially toxic elements (PTEs) such as lead (Pb), zinc (Zn), thallium (Tl), arsenic (As), cadmium (Cd) and antimony (Sb) in the environment as the legacy of past mining activities is a well-known concern worldwide, posing a risk to water resources and human health (El Rasafi et al., 2017). However, the occurrence of metal(loid)s may also represent a resource since large amounts of mine wastes (such as tailings ponds), which normally are the major source of contamination for the surrounding environment, can host valuable amounts of elements of economic interest (Ceniceros-Gómez et al., 2018). The extraction activity at the Raibl mining district (NE Italian Alps) has been documented since 1320 A.D. In its last years of operation, almost 350,000 tons of ore (sphalerite and galena) were mined annually. The Raibl mine was closed in 1991 as the deposits were no longer considered economically viable. The Zn-Pb ore deposit of Raibl includes sphalerite, galena, iron (Fe) sulphides (pyrite and marcasite), and baryte as primary minerals followed by Fe oxy-hydroxides, smithsonite, hydrozincite and cerussite with dolomite and calcite among gangue minerals. Previous investigations on the area reported elevated concentrations of metal(loid)s near mine waste heaps (up to around or over 100 mg/kg for Tl, Sb, Cd, Ge; > 1,000 mg/kg for As; > 1% for Pb and > 10% for Zn and Fe), which are made up of flotation tailings and waste rocks scattered around the mining village and stored in the tailings ponds. Moreover, the weathered tailings showed a high potential as secondary source of Tl and other PTEs in surface and groundwater, especially during periods of high flow river conditions (Barago et al., 2023). Current ongoing research aims to evaluate the occurrence of CRMs in the sludge accumulated in the tailings impoundments following mineral processing for the extraction of Pb and Zn during the mining activity. Some boreholes were performed in the tailings impoundments followed by in the field analyses using portable X-Ray Fluorescence Spectroscopy (pXRF), which is one of the main geochemical analytical techniques employed in multielemental screening for the management of contaminated sites. Electrical Resistivity Tomography (ERT) profiles were executed to estimate the thickness of tailings and evaluate potential correlations with detected metal concentrations. This preliminary survey aided in the collection of representative subsamples for further geochemical characterisation by destructive standard laboratory techniques and extraction procedures thus allowing both to investigate the mobility of Tl and other PTEs in solution as well as to identify volumes of tailings that may represent a potential source of CRMs.