CRITICAL MINERAL POTENTIAL OF PEGMATITES: HOW CLASSIFYING THEIR ZONATION CAN INFORM EXPLORATION

Pegmatites can contain a vast range of minerals, many of which are associated with critical elements, including beryllium, cesium, lithium, niobium, tantalum, and the rare-earth element group. One difficulty within understanding these resources in the U.S. is the lack of adequate terminology to classify pegmatites according to their mineral content for targeted exploration. To better constrain the concentration of critical minerals, the Helen Beryl pegmatite, South Dakota with simple zonation, was compared with the complexly zoned Ray pegmatite, Spruce Pine region, North Carolina. The accessory mineralogy of each was investigated through combined field analyses, literature and mineral chemical analyses.

The Helen Beryl pegmatite has enrichment in beryl and spodumene, which can be well categorized by a geochemical classification such as LCT (lithium-cesium-tantalum). In contrast, the Ray pegmatite, Spruce Pine region, North Carolina, has unusual mineral wealth including columbite-group, lepidolite, beryl, fluorite, elbaitic tourmaline, amazonite, pollucite, and apatite that cannot be adequately classified into a single geochemical group. Micro-XRF analysis of one sample from the Ray pegmatite revealed the complexity of the zonation at Ray with a single columbite-group crystal displaying a Nb-rich core and Ta-rich rim. These data indicate that, at least at Ray, pegmatites are better classified by the accessory mineral scheme of Wise et al. (2022). The Ray pegmatite is a product of residual melt of granitic magmatism (RMG), group 1 type. The value of researching the mineralogy present and accurately classifying pegmatites is key for understanding the resources within these that may help supply the critical minerals for the energy transition.