Fe-Co-Ni mineralization in the Punta Corna hydrothermal vein system (Western Alps, Italy): preliminary results

The Punta Corna Mining District is located in the Lanzo Valleys, North-West of Turin (Italy). It consists of Fe-Co-Ni mineralization which is part of a wider polymetallic hydrothermal vein system occurring throughout the Western Alps. The ore was exploited for Fe and Co, mainly used for pigment production, until the 20th century. The global concern about the “green transition” and Critical Raw Materials (CRMs) supply, such as Co, has raised a renewed interest in old mining sites where the CRMs’ economic potential was not fully investigated. Since 2018 the Junior Exploration Company AltaMin ltd. owns the exploration license of the Punta Corna area for assessing the economic viability of the ore. Mineralization occurring at Punta Corna can be considered a five-element type deposit [1]. The mineralization consists of a complex vein system interpreted as the product of late Alpine (post metamorphic) hydrothermal events [2]. It is hosted in metaophiolites of the Internal Piedmont Zone (IPZ), representing a portion of the Alpine Tethys oceanic lithosphere and its sedimentary cover of Jurassic age [3] and [4]. In this work, we present the results of a detailed geological survey of Punta Corna area and geochemical, petrographic, and mineralogical investigations on several samples from selected veins. Field work was conducted in collaboration with AltaMin Ltd. It focused on geological mapping and a detailed geological-structural study aimed at understanding the brittle deformation stages related to the mineralizing event. Petrographic, mineralogical and chemical characterization of samples collected from different hydrothermal veins using optical microscopy, XRD, wet-chemical analyses, and SEM-EDS techniques were performed at the University of Turin and Milan. The mineralized veins are almost exclusively hosted in metabasic rocks, locally preserving primary basaltic structures, and are associated with a sub-vertical E-W trending faults system. Iron, cobalt, and nickel mostly occur as (di- and tri-) arsenides (i.e., skutterudite and safflorite series), and relative alteration products (erythrite, annabergite); Ag occurs predominantly as Ag sulfides or contained in tetrahedrites, and Cu and Fe (with lesser quantities of Zn) also occur as sulfides. The geochemical composition of the veins is spatially variable within the mining district: the western sector is rich in Fe arising from the abundant presence of Fe minerals (i.e., siderite, ankerite, FeOx), whereas Co and Ni are absent; the central sector shows enrichment in Ni-minerals (i.e., rammelsbergite and Ni-skutterudite), whereas, in the eastern sector, Co and Ni occur at comparable high grades. Gangue minerals are ubiquitous and include calcite, dolomite, siderite, ankerite, quartz, and baryte. Chlorite and white mica are common hydrothermal alteration products.