Lithium, which is an excellent conductor of heat and electricity, became a strategic metal in the past decade due to its widespread use in electromobility and green technologies. The resulting significant increase in demand has revived European interest in lithium mining, leading several countries to assess their own resources/reserves in order to secure their supplies. In this context, we present for the first time a geographically-based and geological compilation of European lithium hard-rock occurrences and deposits with their corresponding features (e.g., deposit types, Li-bearing minerals, Li concentrations), as well as a systematic assessment of metallogenic processes related to lithium mineralization. It appears that lithium is well represented in various deposit types related to several orogenic cycles from Precambrian to Miocene ages. About thirty hard-rock deposits have been identified, mostly resulting from endogenous processes such as lithium-cesium-tantalum (LCT) pegmatites (e.g., Sepeda in Portugal, Aclare in Ireland, Läntta in Finland), rare-metal granites (RMG; 5 3) Peraluminous, high-phosphorus RMG with strong enrichment in Ta, Sn, Li and F, occurring in a continental-collision setting. In this RMG type, Li concentrations can be high, from 0.5% to 1.0% Li 2 O, and occurring as lepidolite, Li-rich muscovite and amblygonite-montebrasite series, such as at
Algoma-type banded iron formations (BIF) are chemical sedimentary rocks characterized by alternating layers of iron-rich minerals and chert that are generally interstratified with bimodal submarine volcanic rocks and/or sedimentary sequences in Archean greenstone belts. However, the geological setting for Algoma-type BIF deposition remains equivocal due to the effects of post-depositional deformation and metamorphism and absence of modern analogues for comparative studies. It is commonly accepted that the abundance of rare earth element and yttrium (REE+Y) in chert bands may retain a primary geochemical signature and therefore constrain their geological setting. In order to explore the latter, a geochemical study using the laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) methodology was done using cherts from four Canadian BIF-hosted gold deposits. These results suggest that chert bands record: (1) interaction of seawater with Fe-oxyhydroxides, as suggested by their heavy REE enrichment coupled with La and Y enrichments; (2) contributions from high-temperature (>250ºC) hydrothermal fluids, as suggested by positive Eu excursions; and (3) detrital contamination, which is suggested by relatively consistent REE concentrations and a chondritic Y/Ho ratio (i.e., Y/Ho ≈ 27). Water-column pH conditions at the time of BIF deposition are evaluated using Ce/Ce*: a positive Ce/Ce* anomaly suggests relatively acidic conditions (i.e., pH ≤ 5) for most of the chert samples, but more alkaline conditions (i.e., pH ≥ 5) for samples showing Fe-oxyhydroxide precipitation within chert bands. Finally, in situ using secondary ion mass spectrometry (SIMS) analysis (n= 73) of chert from Meliadine show the δ 18 O of primary amorphous silica (+27‰) was modified to values of around +8 to +20‰ during diagenesis at temperatures >100°C with a fluid having δ 18 O H2O = 0 to 5‰. Thus, whereas there has been O isotopic exchange during diagenesis, the REEs and trace elements are not modified in the chert due to the low concentrations of these elements in the reacting fluid of sea water origin.
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