ARO - Terrestrial Research Program, Methodologies and Protocols for Characterization of Geomaterials

Abstract : The third and final year of this project continued to focus on the use of laser-induced breakdown spectroscopy (LIBS) for the analysis of geomaterials. LIBS was utilized for geochemical fingerprinting of an extensive suite carbonate minerals, including those of biogenic origin(sea shells), as well as over 200 garnets obtained from locations around the world. A laboratory-based LIBS instrument was used to produce spectral databases that were subsequently analyzed using chemometric techniques such as partial least-squares discriminant analysis(PLSDA), a common approach for performing statistical regression on high-dimensional data. Our results further strengthened support for LIBS being an excellent technique for identification and discrimination of minerals based on geographic origin. We successfully explored the use of a stepwise approach for classifying garnets based on first sorting them into one of six classes based on elemental composition followed by PLSDA analysis for provenance determination. We also began a related collaboration with ACE CRREL that focuses on analysis of ice cores for identification of climate change markers. An ongoing goal of our research has been to transition from laboratory-based instruments to the use of handheld LIBS systems for field operations. Though our efforts to obtain funding for such instrumentation did not come to fruition during the time period covered by the grant we now have access to a handheld LIBS unit and plan to repeat many of the same analyses to see if the levels of discrimination are similar. Based on our work over the last several years we did contribute a book chapter dedicated to LIBS-based geochemical fingerprinting.