PROVENANCE OF TOURMALINE USING LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS) AND CHEMOMETRIC ANALYSIS

Tourmaline is a chemically and mechanically resistant borosilicate that records the geochemical environment in which it forms and thus is an excellent indicator of provenance (defined as the lithology in which the tourmaline crystallized). Laser-Induced Breakdown Spectroscopy (LIBS) and chemometric analyses provide constraints on tourmaline provenance preferable to electron microprobe analysis for three main reasons: (1) LIBS analysis is sensitive to light elements such as Li, B and H; (2) LIBS spectra include a large amount of useful information including elemental concentrations, isotopic information, and matrix effects that provides a unique spectral fingerprint of each tourmaline; and (3) LIBS analysis is rapid and inexpensive, allowing analysis of many samples. Because tourmaline is stable over a wide range of P-T-X conditions, tourmaline provenance can help refine detrital mineral suites. Our data indicate that tourmaline provenance can be assigned to seven categories: (1) Li-rich pegmatites; (2) hydrothermally altered aplites and diorites; (3) Li- and Al-rich pegmatites; (4) Ti-rich tourmalinites; (5) Na-rich leucocratic granites; (6) Cr- and V-rich sediments; and (7) F- and B-rich granites (c.f. Henry and Guidotti, Am.Min., 1985).

Tourmaline from a variety of world-wide localities were analyzed using an Ocean Optics © 2500+ LIBS instrument with an Nd-YAG laser that emits light at 1064 nm. Principal component analysis (PCA) and partial least squares regression (PLSR) were used to determine the provenance of tourmaline by calibrating and validating the provenance model with crystals of known provenance. These data provide a new technique to facilitate provenance determination in this widespread, petrogenetically important mineral.