The role of pegmatites and acidic fluids for hydrothermal Zr and REE transport in the Strange Lake peralkaline granitic pluton

Strange Lake is mid-Proterozoic peralkaline granitic pluton located in Quebec/Labrador, Canada. It is a world class REE-Zr-Nb mineral deposit host to two potential ore zones (the B zone and Main zone). Several studies have demonstrated that hydrothermal processes have played a significant role for metal mobilization and mineralization in this system (Salvi and Williams-Jones 2006, and references therein). The mineralization in the B zone occurs in pegmatite-rich domains, where it was shown that >90 % of the mineralized REE and Zr occurs in hydrothermal minerals with a significant secondary enrichment process (Gysi et al. 2016). The hydrothermal alteration can be spatially related to the pegmatites, which were interpreted to be the source of saline acidic HF-HCI-bearing fluids (Gysi and Williams-Jones 2013). I present here the different alteration types related to these pegmatitic fluids by combining field observations at the outcrop and thin section scales with mineral and bulk rock compositions to illustrate the effects of hydrothermal fluid rock reactions on chemical mass fluxes and associated ore mineralization. Numerical modeling of fluid-rock equilibria is used to explore the controlling factors for REE and Zr mobilization in these hydrothermal fluids, and discuss the key factors affecting metal mobility at Strange Lake.