Date of Award

Spring 1-1-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Joseph Smyth

Second Advisor

Markus Raschke

Abstract

Gadolinite is a monoclinic orthosilicate mineral that is part of the Gadolinite Supergroup of minerals. It occurs in beryllium and rare earth element (REE) bearing granites, pegmatites, and some metamorphic rocks (Baćík et al., 2014). The White Cloud Pegmatite is a small but rare earth element rich NYF (niobium-yttrium-fluorine) pegmatite located in the South Platte Pegmatite district of Colorado, USA. It is associated with the 1.08Gy (Smith et al., 1999) granitic Pikes Peak Batholith. The gadolinite in the White Cloud Pegmatite ranges from strong HREE (heavy rare earth element) to LREE (light rare earth element) dominant species. The gadolinite occurs in close association with other REE minerals such as thalénite, fergusonite, allanite, yttrian fluorite, bastnäsite, synchysite. We explored the crystal chemistry and structure of two petrographically distinct samples by electron microprobe chemical analysis (EMPA), single crystal X-ray diffraction (XRD), and Raman spectroscopy. One sample (Z2A) shows nearly full occupancy of Fe, and partial substitution of Si for Be in the Q tetrahedral site with slight substitution of Be into the T-site. The second sample (SWC) has up to 15% vacancy in the Fe site and up to 15% disorder between Be and Si tetrahedral sites. The Be-Se partial disorder indicates that Be may substitute for Si in natural systems and be more abundant than previously thought. The different REE distributions indicate that gadolinite can accept a broad range of rare earth element cations.

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