PROVENANCE DETERMINATION OF CASSITERITE ORE CONCENTRATES USING LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is a versatile atomic emission spectroscopic technique for elemental analysis of materials in real-time being developed for man-portable application in the field. Since the LIBS plasma emission spectrum reflects the chemical composition of the sample, it represents a ‘geochemical fingerprint’ that provides a means of rapidly distinguishing amongst different geographic sources for a geological material. This attribute of LIBS, together with its field-portable potential, makes the technology an appropriate choice for many geoscience applications, including chemical analysis for provenance determination. Cassiterite is a tin oxide mineral (SnO₂) that, from ancient times to the present, has been the chief source of metallic tin. Determining the geographic origin of cassiterite ore is of interest since it is one of the natural resources mined in areas associated with armed conflict and human rights abuses, such as the Democratic Republic of the Congo (DRC), and can therefore be considered a ‘conflict mineral’. The Dodd-Frank Act of 2010 holds U.S. companies responsible for disclosing the source of the raw materials used in their products. This presentation will describe our efforts to use the fingerprint of the LIBS broadband spectrum as a mean to classify cassiterite samples based on geographic origin. Two sample suites of pulverized cassiterite ore concentrate - 9 samples from 5 regions in Indonesia and 38 samples from 3 South American counties (Bolivia, Peru & Brazil) and 3 Southeast Asian countries (Malaysia, Thailand & Indonesia) - were analyzed using a commercial laboratory-based LIBS system (Applied Spectra, Inc. RT-100-HP/EC). The Partial Least Squares Discriminant Analysis (PLSDA) pattern recognition method was used to achieve high rates of classification success. These results reinforce the idea that LIBS has the potential to be utilized in the field as a means of in situ attribution of ores to their source area.