LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS): APPLICATION OF A HANDHELD ANALYZER TO A LITHIUM PEGMATITE PROSPECT IN THE CAROLINA TIN-SPODUMENE BELT

The Carolina Tin-Spodumene Belt contains numerous pegmatites of Carboniferous age in a 0.5 to 3 km-wide domain across the Kings Mountain Shear Zone, including the most extensive and historically important Li pegmatite deposit in North America. Pegmatites here consist of (i) barren pegmatites composed of either K-feldspar, albite, and quartz or containing K-feldspar, oligoclase, quartz with accessory muscovite, biotite, and garnet and (ii) fertile Li-enriched pegmatites typically consisting of spodumene, K-feldspar, albite, quartz, and beryl. Individual Li-enriched pegmatites are complex structures with surface dimensions of a few to a hundred meters in width and up to a kilometer in length that were intruded generally parallel to the foliation of the surrounding metamorphic country rocks.

LIBS is a form of atomic emission spectroscopy in which pulsed laser light is tightly focused to ablate a minute amount of a sample and create a plasma in which constituent elements can be detected and identified through spectral analysis of emitted light. Because all elements have at least one emission line over the spectral range between 200-900 nm, any element can be analyzed by LIBS in situations where its abundance is above the limit of detection in the material. The recent introduction of commercial handheld LIBS analyzers has facilitated the rapid acquisition of geochemical analysis in situ in the field, with potential application to resource exploration and grade control during mining and ore beneficiation.

Handheld LIBS analyses have been undertaken on a large Li-pegmatite prospect in Gaston County, NC at multiple outcrops, on drill core, and for mineral separates in three contexts: (i) element detection and mineral identification, (ii) compositional imaging (microchemical mapping and depth profiling), and (iii) elemental quantitative analysis for Li, K, Rb, and Cs. The results from this study, in which fertile Li-enriched pegmatites were distinguished from barren pegmatites, highlight the potential of handheld LIBS to rapidly determine the degree of pegmatite fractionation and drastically reduce the time necessary to acquire compositional information for an exploration program.