Pingitore, et al., reported in 2018, that the electron microprobe can map the spatial distribution of elements in a rock at a sub-mineral-grain scale to provide a basis for understanding mineralization processes and to determine optimal strategies for extraction of valuable target elements. Round Top Mountain (near the town of Sierra Blanca, Hudspeth County, west Texas, USA) is a peraluminous rhyolite laccolith that is homogeneously mineralized at over 500 ppm rare earths, more than 70% of which are yttrium and heavy rare earths (YHREEs).
The massive deposit is exposed at the surface as a mountain some 2 km in diameter and 375 m in height. Round Top Mountain also contains Li, Be, U, Th, Nb, Ta, Ga, Rb, Cs, Sn, and F. The valuable YHREEs are hosted in yttrofluorite, which is soluble in dilute sulfuric acid. Texas Mineral Resources Corporation proposes to surface mine, crush, and heap leach the deposit. The distribution of YHREEs, and that of other trace elements, is remarkably homogeneous at outcrop drill hole scale. Here the authors document that YHREE mineralization appears pervasive through the rhyolite at a millimeter scale. Back scattered electron (BSE) and characteristic X-ray maps reveal the fine-grain size and apparently random and dispersed spatial distribution of the yttrofluorite that hosts Round Top’s valuable YHREEs.
The yttrofluorite grains do not appear to cluster at special mineralized locations, e.g., in pores or along cracks in the rhyolite. The same is apparently true of such other potentially valuable minerals as cassiterite and uranium species. These findings confirm that the distribution of YHREEs in Round Top Mountain rhyolite is homogeneous through different orders of magnitude of scale, i.e. , from outcrop (as seen in the companion work in this volume) to sub-thin section. The material thus is ideal for a heap leach operation where homogeneous feedstock is crucial to consistent and economic operation. The findings also confirm and explain why mechanical separation would prove very difficult and expensive due to the astronomical number of yttro-fluorite grains in even a golf-ball-size piece of Round Top rhyolite.
The authors conclude that These findings confirm that the distribution of YHREEs in Round Top Mountain rhyolite is homogeneous through different orders of magnitude of scale, i.e. , from outcrop (as seen in the companion work cited below) to sub-thin section. The material thus is ideal for a heap leach operation, where homogeneous feedstock is crucial to consistent and economic operation. The findings also confirm and explain why mechanical separation would prove very difficult and expensive due to the astronomical number of yttrofluorite grains even in a golf-ball-size piece of Round Top rhyolite. Microprobe mapping has proved important to our understanding of rock processing on a bulk scale. It helps to explain why some elements leach effectively from the rhyolite and others do not. That knowledge can guide optimization of the recovery process, a change in technical approach to recovery, or abandonment of the pursuit of a potential byproduct target element.
[2019 NI-43-101 Report for Sedex: http://tmrcorp.com/_resources/reports/TMRC-NI43-101-PEA-2019-16-August-2019.pdf ]
[Companion work: http://www.i2mconsultants.com/downloads/corp/AMPC_2018010814293996.pdf ]
[See company developing the deposit: http://tmrcorp.com/projects/rare_earths/ ]
[An earlier paper on the Round Top Deposit: http://tmrcorp.com/_resources/reports/2014_Jan_Journal_RE_32.pdf ]
[Related paper on origin of REEs via rifting: http://www.i2mconsultants.com/downloads/corp/Piccione1958.pdf ]
[Petrogenesis HREE Round Top: http://www.i2mconsultants.com/downloads/corp/minerals-08-00423.pdf ]
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