Mineralogical, petrogenetic, and geochemical characteristics of the Meldon Aplite and its implications to Cornwall and Devon for rare- element pegmatite exploration

Abstract

Recent development of high-tech industries and the global drive towards a carbon free economic have placed a tremendous demand on Li and placed substantial importance on exploration of lithium deposits. The Meldon Aplite has long been described as unique feature across SW England in terms of its mineralogy and exception enrichment in rare-element such as lithium, caesium, fluorine, phosphorous and niobium-tantalum. The Meldon Aplite present a potential for lithium mineralization. This study has identified a range of lithium rich minerals in the Meldon Aplite including lepidolite, elbaite, petalite, amblygonite-montebrasite, and eucryptite. It has equally ruled out the presence of spodumene in the aplite. Mineralogy and textural studies conducted in this study resulted in the identification of four different crystallization stages. These are magmatic, magmatic-hydrothermal, hydrothermal and supergene stages. In terms of lithium mineralisation, lepidolite, elbaite, petalite and amblygonite-montebrasite are primary magmatic phases with eucryptite forming at the expenses petalite complete hydrothermal replacement and clay montmorillonite forming from petalite weathering. The close association of amblygonite-montebrasite with fluorapatite indicate that it is altered at a certain extent. From trace element, the Meldon Aplite is characteristically enriched in Li (2626 to 5569 ppm), Cs (75 to 612ppm), Rb (940 to 2540 ppm), and moderately enriched in Be (8 to 84 ppm), Ta (11 to 49 ppm), and Nb (35 to 90 ppm). Such geochemistry suggest that the Meldon Aplite is relatively evolved. Comparison of Tellus (2014) soil data with the Meldon Aplite geochemistry has delineated six zones with high caesium and tantalum concentration, geochemically comparable to the Meldon Aplite. These are underlain by metasedimentary rocks, metabasic rocks and on one occasion by Gunnislake granite. The Meldon Aplite extent cannot be traced with surface exposure, however soil samples close to the aplite contain relatively elevated Rb (>62ppm).