LASER INDUCED BREAKDOWN SPECTROSCOPY ANALYSIS OF ZONES IN LIDDICOATITES FROM ANJANABONOINA PEGMATITE, MADAGASCAR

The brilliantly zoned liddicoatite tourmalines from the Anjanabonoina pegmatite in central Madagascar contain a record of changing magma and fluid composition. These Ca-Li-Al-rich crystals have distinct purple and green radial zones that are unique to all other known liddicoatite localities, and previous Electron Microprobe (EMP) studies on these zones reveal that some are Ca-rich, while others are Ca-poor (Lussier et al., 2011). Laser-Induced Breakdown Spectroscopy (LIBS) analysis rapidly provides information about the concentrations of every element (H – U), as opposed to the thirteen elements determined by EMPA. A transect of LIBS analyses from core to rim of an Anjanabonoina liddicoatite confirmed a Ca fluctuation between zones as well as fluctuation of other components. A LIBS decision tree consisting of Partial Least Squares Regression models developed by Mount et. al (2018) determined that liddicoatite Ca-rich zones have compositions more similar to tourmaline from marble hosts and that the Ca-poor zones are similar to pegmatitic tourmaline. LIBS provides a comprehensive view of elemental fluctuation between and within each zone, giving more insight into the chemistry of fluids present during crystallization. These results indicate the Anjanabonoina liddicoatite zones were generated by tourmaline growth during mixing of waters from the marble host and the pegmatite in variable proportions. This research demonstrates LIBS application in mineralogy, improves upon our understanding of complex mineral zoning, and explores the origin of an anomalous mineral.