Joint Logan Club/OCGC Seminar Series - Dr. Anthony Williams-Jones, McGill University & SEG Distinguished Lecturer

The Joint Logan Club and Ottawa-Carleton Geoscience Centre Seminar Series is pleased to host Dr. Anthony Williams-Jones: McGill University & SEG Distinguished Lecturer

Thursday, November 28, 2013
11:30 AM
Marion Hall (MRN) 127
University of Ottawa

REE ore genesis - The current state of knowledge

Economic or potentially economic REE deposits are hosted by or genetically associated with alkaline igneous rocks and carbonatites. Primary REE enrichment in silicate magmas depends on the highly incompatible nature of the REE, may be facilitated by fluoride complexation, and occurs at late stages of magma evolution through crystal settling and crystallisation of residual, fluid-saturated liquids including immiscible fluoride melts. Carbonatite magmas likely owe their REE enrichment to the high solubility of the REE, and their preference for the LREE to the similar ionic radii of Ca2+ and Ce3+; HREE are smaller.

Hydrothermal mobilisation may be essential to the economic viability of many REE deposits. Indeed, the World’s largest deposit, Bayan Obo, China, is dominantly hydrothermal. Although aqueous fluoride complexes are widely thought to be the main agent of REE transport, modelling of natural systems suggests that this is not the case. Instead, chloride complexes appear to be responsible for REE transport. Moreover, experiments suggest that REE chloride complexes can cause the observed preferential LREE mobility. Hydrothermal concentration of REE occurs when interaction of acid REE-Cl-bearing fluids with pH-buffering rocks, or mixing with neutral fluids, and/or decreasing temperature, induces REE mineral deposition.