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The Hoidas Lake rare earth element (REE) deposit, located in northern Saskatchewan, Canada, is a structurally controlled vein-type LREE deposit with allanite-(Ce) and fluorapatite as the main REE carriers. The mineralized veins cut Archean and Paleoproterozoic orthogneisses and supracrustal rocks of the southern Rae Subprovince. The paragenesis includes hyalo-phane- bearing pegmatite dikes, REE-mineralized allanite-, diopside-, hornblende-, hyalophane-, and titanite-bearing veins, and later breccia veins that contain several stages of apatite. The mineralized veins record hydrothermal alteration with nucleation of monazite and REE-carbonate inclusions in apatite and allanite, respectively. Barren quartz-, carbonate-, and hematite-rich veins represent the final stage of hydrothermal activity. Samples from the hyalophane-bearing pegmatites, apatite breccia veins, and quartz-carbonate veins, used for fluid inclusion petrography and microthermometry, indicate four distinct fluid inclusion assemblages (FIAs): (1) carbonic inclusions showing LCO2(liquid CO2) + VCO2(CO2vapor) phase composition with 20-40 vol.% VCO2at 0 C; (2) aqueous inclusions showing L (liquid H2O) + V (H2O vapor) phase composition with 90-100 vol.% V at 20 C; (3) aqueous inclusions showing L + V + H (halite) phase composition with 15 vol.% V at 20 C; and (4) aqueous L + V inclusions with 15-20 vol.% V at 20 C. Type 1 inclusions homogenize to liquid CO2with Th(CO2) from 3.3 to 30.5 C. Type 2 V-rich inclusions have high salinities and contain salts other than NaCl. Type 3 L-V-H inclusions have different homogenization behavior in quartz of the hyalophane-bearing pegmatites (L+V+H L+V L) compared to quartz-carbonate veins (L+V+H L+H L), and Th (total homogenization) values range from 180 to 315 C with salinities of 30-40 wt.% eq. NaCl. In type 4 inclusions Th ranges from 90 to 290 C, but for specific samples and FIAs (fluid inclusion assemblages) there is a more limited spread (from 5 to 25 C). Salinities range from 8 to 24 wt.% eq. NaCl, and the inclusions have variable Na/(Na + Ca). Evaporate mound analysis shows average normalized (to 100%) cation contents of 48% Na, 24% Ca, 6% K, 5% Ba, 4% Mn, 2% Fe, 2% Mg, and 9% Sr for quartz-hosted inclusions in quartz-carbonate veins, and 61% Na, 32% Ca, and 7% K for quartz-hosted inclusions in hyalophane-bearing pegmatite dikes. The thermometric and chemical data suggest that evolution of the Hoidas Lake mineralization involved two fluid types with early entrapment of a carbonic fluid followed by introduction of a mixed Na-Ca-K-(Ba-Mn-Mg-Fe-Sr) aqueous fluid with variable salinities that was responsible for the late alteration of the mineralized veins. Furthermore, the inclusion data provide constraints on entrapment temperature (310 C) and also indicate that the pressure was transient (0.5 to 2 kbars) based on the homogenization temperature data for the carbonic (type 1) and aqueous L-V-H (type 3) inclusions.

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Compilation and indexing terms, Copyright 2018 Elsevier Inc.<br/>20151600751513<br/>Evaporate mound analysis<br/>Fluid inclusion<br/>Fluid inclusion assemblages<br/>Fluid inclusion microthermometry<br/>Fluid inclusion petrography<br/>Homogenization temperatures<br/>REE mineralization<br/>Remobilization