CHARACTERIZING THE CRITICAL ELEMENT CHEMISTRY OF EUDIALYTE, FROM THE KIPAWA ALKALINE COMPLEX, QUEBEC, CANADA

Transitioning to lower carbon energy requires new mineral resources and reinvestigating known resources, specifically, characterizing the chemical compositions of unusual minerals. One such mineral is eudialyte (eud), ideally Na₁₅Ca₆Fe₃Zr₃Si(Si₂₅O₇₃)(O,OH,Cl)₃(OH,Cl)₂, a REE-bearing zirconosilicate with extensive solid solution. A sample of a 12-cm eudialyte-bearing rock slab, from the Kipawa Alkaline Complex, Quebec, Canada, was texturally characterized primarily by BSE and chemically characterized for major and minor elements with the EMPA. The primary mineralogy of the sample consists of eud, fluor-amphiboles, agrellite (NaCa₂Si₄O₁₀F), and hainite (Na₂Ca₄(Y,REE)TiSi₄O₁₄OF₃). Trace phases include plagioclase, K-feldspar, apatite, monazite, fluorite, and graphite. Imaging and chemical analyses show minor chemical differences in the eudialyte, primarily (NaK)_-1, (LaCe)_-1, and (FeMn)_-1. An average chemical formulae for multiple analytical spots on two large (3-5 cm) eudialyte grains is: (Na_12.38Ca_1.76Y_0.47REE_0.21K_0.20Sr_0.02)(Ca_6.00)(□_1.4Fe²⁺_1.0Mn²⁺_0.60)(Zr_2.85Ti_0.08)(Si_0.98Nb_0.08Al_0.03)(Si_24.97O₇₃)(OH_3.00)(Cl_1.10OH_0.90). Measured REEs include Ce, La, and Nd and are contained within the eudialyte, hainite, and monazite. Average critical element abundances within eud are, in wt %: 8.84 - Zr, 0.70 - Y, 0.30 - Ce, 0.13 - Nb, 0.13 - La, and 0.07 - Nd. Adjacent to the eud, tabular amphiboles are fluoro-richterite and fluoro-edenite; both include rounded grains of K-feldspar. A later generation of anhedral interstitial amphiboles are magnesio-fluoro-arfvedsonite in composition. Agrellite crystals are altered; either psuedomorphed by apophyllite or have apophyllite rinds suggesting later stage, lower temperature fluid infiltration. Eudialyte has potential to contribute to the global need for Zr as a primary critical element resource and potentially may serve as a secondary Y+REE+Nb resource if additional deposits can be located. Critical element concentrations of eudialyte measured here concur with previous studies from the Kipawa Alkaline Complex, with a concentration of Zr < 4.0 apfu. In this sample, the inclusion-free chemically homogenous eudialyte was not affected by later fluid alteration allowing for the preservation of critical element concentrations through later hydrothermal events.