ASSESSMENT OF PROVENANCE OF CONFLICT MINERALS USING LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

Several minerals, including cassiterite, columbite, gold, rubies, tantalite, and wolframite, are of interest as conflict minerals in part due to the Dodd-Frank Act, signed into law on July 21, 2010. Section 1502 adds additional reporting requirements for companies’ SEC filings on the sources of “conflict minerals” and the Tom Lantos Block Burmese JADE Act of 2008, which restricts the import of gems from Myanmar. To comply with such legislation, it is necessary for companies using these materials to determine accurately the countries of origin (provenance) of minerals. This is a geochemically complex problem that has eluded conventional analytical techniques that employ binary or ternary provenance diagrams. In contrast, Laser Induced Breakdown Spectroscopy (LIBS) is a rapid, field-deployable technique that collects the light emitted as atoms cool in laser-ablation plasma. All elements emit photons in the range of wavelengths collected. Thus, LIBS spectra are complex geochemical fingerprints of mineral composition, including major, minor, and trace elements. In this pilot study, LIBS spectra (40,000 wavelengths between 200 and 1000 nm) on a statistically valid sample set are used to build a database for each mineral. Cross validation of the sample set using advanced signal processing techniques and chemometric analysis of LIBS data are successful for the identification of provenance of conflict minerals, because of the large number of variables collected, and the depth of information recorded in LIBS spectra. In the case of rubies, sapphires, and emeralds, country of origin is correctly identified with accuracy of 98%. Analysis of other conflict minerals is ongoing. Advantages of using LIBS to identify and track conflict minerals include ease of operation and portability, eliminating the need to analyze samples in the laboratory and permitting analysis at border crossings and other strategic locations.