From extractive waste to valuable resources: potential critical raw material recovery and contemporary environmental mitigation in the gold mines of the Western Alps (NW Italy)

Extractive waste (EW) represents a significant environmental concern but also a strategic resource opportunity within the framework of the circular economy. This study focuses on the former Crocette and Pestarena gold mines in the Western Alps (NW Italy), which have left behind a significant environmental legacy. The study area is an alpine valley where paragneiss, micaschists and orthogneiss outcrop. At the valley floor, the metamorphic bedrock is covered by alluvial deposits hosting a phreatic aquifer that is hydraulically connected to surface waters.

The research focuses on EW deposits characterisation to assess both their potential for Critical Raw Materials (CRMs) recovery and the level of contamination and potential ecological risk affecting soils and sediments in the mining area.

The study integrates a significant collection of previously unpublished data, mainly focusing on EW and soils, with a 2024 sampling campaign to improve the understanding of EW deposit extension and to investigate their physical, geochemical and mineralogical characteristics.

Results reveal a matrix dominated by quartz, feldspars, and micas, along with secondary minerals (e.g. scorodite and jarosite) indicative of alteration processes. Residual pyrite and arsenopyrite, together with traces of scheelite and Ce-monazite, highlight the presence of associated CRMs. Geochemically, a significant enrichment of CRMs is detected, primarily driven by As, and secondarily by W, Sb, and Bi, with minor enrichment of Light Rare Earth elements (LREEs).

The environmental impact assessment identifies As as the main pollutant, classifying surrounding soils as heavily to extremely contaminated; Pb contamination is moderate. Overall, the potential ecological risk remains moderate. River sediments are uncontaminated; however, sediments from mine drainage tunnels and EW drainage channels also show contamination and potential ecological risk, confirming that environmental impacts are still ongoing more than six decades after mine closure.

The findings suggest that As, which represents the primary source of contamination at the site, is also the element with the greatest recovery potential. The recovery of As would not only ensure an additional supply of CRMs but could also, potentially, contribute to the mitigation of contamination at the site itself. This feasibility is further enhanced when As recovery is considered in conjunction with associated CRMs (Bi, Sb, and W). The estimated volumes of EW and their residual CRMs content indicate a significant potential for concurrent recovery. Overall, these results point toward a more sustainable mitigation strategy, by which part of the remediation costs could be offset by revenues derived from the recovery and commercialization of As and other CRMs, thereby coupling environmental risk mitigation with the valorisation of strategic resources.