166-5 The Complex Critical Mineral Assemblage of Lower Crustal Sulfide Deposits – A case study from the Ivrea-Verbano Zone in Italy

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones

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Critical mineral demand is expected to rise steadily over the next decades. Consequently, discovering new deposits is pivotal to ensuring long-term critical mineral supply. Because most giant ore deposits formed near the surface, exploration models often focus on the uppermost levels of the crust. However, exploration efforts have been increasingly inefficient over the past decade and resulted in remarkably few discoveries. In contrast to upper crustal rocks, exhumed deep lithospheric settings are often neglected in mineral exploration, but represent intriguing exploration targets such as in the Ivrea-Verbano Zone (IVZ) in northwest Italy.

The IVZ is a cross-section of the subcontinental lithospheric mantle and continental crust that was exhumed during the Alpine Orogeny. The region contains five 300-m-wide mafic-ultramafic pipes that formed from partial melting of fertilized mantle pockets in a post-collisional setting between 278-249 Ma. Metasomatism ca. 190 Ma ago introduced metals into the pipes and resulted in the formation of semi-massive sulfide ore rich in nickel (~12 wt.%), copper (~11 wt.%), and cobalt (~1 wt.%), with ppm-level concentrations of platinum-group elements (PGE), gold, silver, tellurium, cobalt, molybdenum, rare earth elements (REE), and more. The ore assemblage is notably complex and its detailed characterization is key to inform geometallurgical extraction. Common magmatic sulfides include chalcopyrite (CuFeS₂), pentlandite (Ni,Fe)₉S₈, and pyrrhotite Fe_(1-x)S) with minor violarite (FeNi₂S₄), cubanite (CuFe₂S₃), mackinawite  (Fe,Ni)S and pyrite (FeS₂). PGE minerals primarily occur as sulfarsenides (e.g., irarsite, IrAsS) and tellurides (e.g., merenskyite, PdTe₂). Other tellurium minerals include melonite (NiTe₂), hessite (Ag₂Te), altaite (PbTe) and pilsenite (Bi₄Te₃), often with ppm-level amounts of Pt and Pd. The pipes also contain locally abundant molybdenite (MoS₂), sphalerite (ZnS), cobaltite (CoAsS), gersdorffite (NiAsS), graphite (C) and apatite Ca₅(PO₄)₃(OH,F,Cl) with several thousand ppm REE.

Including exposed lower crustal settings like the IVZ into exploration models is a promising path towards opening new search space for ore deposits. In such a scenario, exploration models should focus on post-collisional settings with a lithospheric architecture that allows for focused metasomatic mass transfer, such as pipes, conduits or the edges of a batholith. Although the pipes do not represent major, high-tonnage ore systems, their complex metal assemblage makes them valuable exploration targets, particularly if future extraction techniques can utilize methods (e.g., in-situ leaching) capable of extracting a wide range of elements simultaneously.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7902

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