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Extreme enrichment and post-magmatic hydrothermal mobilization of the rare earth 22 elements (REE), Zr and Nb have been reported for a number of anorogenic peralkaline 23 intrusions, including the world-class REE-Zr-Nb deposit at Strange Lake, Quebec, 24Canada.Establishing lithogeochemical vectors for these types of deposits is a challenging 25 task because the effects of hydrothermal processes on element distribution are poorly 26 known and the relationships of alteration types to mineralization stages have not been 27well documented.Here, we present results of a detailed mineralogical and geochemical 28 investigation involving a dataset of over 500 mineral and bulk rock analyses of a NE-SW 29 section through the potential ore zone at Strange Lake.Based on these data, we develop a 30 model that explains the role of hydrothermal processes in concentrating metals in 31 peralkaline granitic systems, and identify lithogeochemical vectors for their exploration.32The B Zone, located along the northwestern margin of the Strange Lake pluton, 33 contains a lens-shaped pegmatite-rich domain comprising sub-horizontal sheets of 34 pegmatites hosted by granites with a total indicated resource of 278 Mt grading 0.93 35 wt.% total rare earth oxides (TREO), of which 39 % are heavy (H)REE.Within this 36 resource, there is an enriched zone containing 20 Mt of ore grading 1.44 wt.% TREO, of 37 which 50 % are HREE.The pegmatites are characterized by a core enriched in quartz, 38 fluorite and light (L)REE fluorocarbonates, and a granitic border enriched in 39 zirconosilicates and granitic minerals.The pegmatite sheets and surrounding granites 40 evolved in three essential stages: I) a magmatic stage, II) a near neutral hydrothermal 41 stage involving their interaction with NaCl-bearing orthomagmatic fluids, and III) an 42 acidic hydrothermal stage (comprising high (IIIa) and low (IIIb) temperature substages) 43 that resulted from their interaction with pegmatite-sourced HCl-HF-bearing fluids.Stage 44 IIIa led to pseudomorphic mineral replacement reactions (e.g., Na-Ca exchange during 45 replacement of zirconosilicates) and formation of an aegirinization/hematization halo 46 around the pegmatites.In contrast, Stage IIIb, which was responsible for the 47 hydrothermal mobilization of Zr and REE, is manifested by fluorite and quartz veins, 48 zircon spherules, gadolinite-group minerals, gittinsite and ferriallanite-(Ce) and a 49 pervasive replacement of the granite by these minerals.The distribution of REE, Zr, Nb 50 and Ti was controlled by the competition between hydrothermal fluids and the stability of 51
Gysi et al. (Mon,) studied this question.