Remarkably Consistent Rare Earth Element Grades at Round Top Yttrofluorite Deposit

Abstract

The peraluminous rhyolite that forms Round Top Mountain (approximately 375 m high × nearly 2 km in diameter), near Sierra Blanca, Hudspeth County, west Texas, USA, is enriched in yttrium and heavy rare earth elements (YHREEs), as well as Li, Be, U, Th, Sn, F, Rb, Cs, Nb, and Ta. Texas Mineral Resources Corp. (USA) proposes to release the YHREEs from their unique yttrofluorite host via heap leaching with dilute sulfuric acid. The inexpensive process also releases portions of valuable byproduct Be, Li, and U from accessory minerals amid the insoluble feldspars and quartz that comprise 90% -95% of the surface-exposed rhyolite mountain. The objective of this study is to determine the consistency of mineralization grade, an important consideration in mine planning and preliminary economic analysis. The method is to plot elemental analyses of Y, Dy, Ho, Tm, Yb, Ce, Pr, Nd, Eu, Gd, Tb, U, and Nb from more than 1400 reverse circulation cuttings taken from 64 exploration drill holes against sample depth. The result of inspection of the plots reveals a remarkably homogeneous distribution of minor and trace elements throughout the sampled portion of the massive, 1.6-billion-tonne laccolith. The plots drive the conclusion that Round Top mine feedstock should remain constant for the life of the mine (multiple decades). Thus mining mechanics could be optimized at the start of operations and not require expensive later changes. The physical and chemical design of the heap leach and recovery and purification of target elements from pregnant leach solution also could be perfected during early development.

ArcGIS<sup>TM</sup> and Principal Component Analysis of Probe Data to Micro-Map Minerals in Round Top Rare Earth Deposit

“…The similarities among the studies emphasize the earlier finding that the mineralization at Round Top is remarkably homogeneous [8]. That earlier geochemical study involved some 1400 samples from more than 100 drill holes spread across the mountain.…”

“…In all 7 thin sections the highest weighted variables comprising the first 3 PCs were K, Al, Si, and Na. These four elements are known from bulk elemental analyses [8] [12] to make up approximately 90% or more of Round Top rhyolite. The three minerals corresponding to the first 3 principal components are the major minerals of the Round Top rhyolite: orthoclase feldspar (K-spar, KAl-Si 3 O 8 , monoclinic), plagioclase feldspar (albite, NaAlSi 3 O 8 , triclinic) and quartz (SiO 2 , trigonal).…”

“…Round Top Mountain underwent chemical alteration by a late-stage fluorine vapor phase that enriched it in HREEs and other incompatible elements [2] [6] [12]. In the search for and delineation of mineral deposits from Round Top Mountain previous studies [3] [8] [9] have included standard methods such as the collection of rock samples and preparation of thin sections for analysis with optical petrography and scanning electron microscopes. Electron probe microanalysis (EPMA) employs an electron beam excitation to determine the elemental composition of individual grains or portions of grains in thin sections [13].…”

Microprobe Mapping of Rare Earth Element Distribution in Round Top Yttrofluorite Deposit

“…In a companion paper in this volume (Remarkably Consistent Rare Earth Element Grades at Round Top Yttrofluorite Deposit) we documented the unusual homogeneity of the mineralization grade of the deposit at the scale of a set of exploratory drill holes that sampled roughly half of the exposure of massive Round Top Mountain [30]. In this current contribution we examine the rhyolite at a much finer scale to understand the microscopic distribution of the acid-soluble yttrofluorite that hosts the primary target YHREEs.…”

Past, Present, and Future of Texas Industrial Minerals

“…The demand for rare earth elements, a diverse group of metals used in a variety of technology applications from wind turbines to guidance systems, has increased recently with REE prices majorly affected by restrictions in the international supply of the refined metals. The Paleogene Round Top laccolith in western Texas has been evaluated for its rare earth element potential, as well as localized concentrations of beryllium and uranium [18,33,34]. Other similar shallow igneous intrusions remain to be evaluated.…”