TECHNICAL NOTE Can the provenance of the conflict minerals columbite and tantalite be ascertained by laser-induced breakdown spectroscopy? Russell S. Harmon & Katrina M. Shughrue & Jeremiah J. Remus & Michael A. Wise & Lucille J. East & Richard R. Hark Received: 11 February 2011 /Revised: 11 April 2011 /Accepted: 12 April 2011 /Published online: 3 May 2011 # Springer-Verlag (outside the USA) 2011 Abstract Conflict minerals is a term applied to ores mined in conditions of armed conflict and human rights abuse. Niobium and tantalum are two rare metals whose primary natural occurrence is in the complex oxide minerals columbite and tantalite, the ore of which is commonly referred to as coltan. The illicit export of coltan ore from the Democratic Republic of the Congo is thought to be responsible for financing the ongoing civil conflicts in this region. Determining the chemical composition of an ore is one of the means of ascertaining its provenance. Laser- induced breakdown spectroscopy (LIBS) offers a means of rapidly distinguishing different geographic sources for a mineral because the LIBS plasma emission spectrum provides the complete chemical composition (i.e., “chem- ical fingerprint”) of any material in real time. To test this idea for columbite–tantalite, three sample sets were ana- lyzed. Partial least squares discriminant analysis (PLSDA) allows correct sample-level geographic discrimination at a success rate exceeding 90%. Keywords Laser-induced breakdown spectroscopy . LIBS . Conflict minerals . Columbite–tantalite . Coltan . PLSDA Introduction Niobium (Nb) and tantalum (Ta) are rare metals of commercial value, and the high demand for these elements has resulted in an increase in exploration programs to locate new ore deposits. The primary natural occurrence of Nb and Ta is in the complex oxide minerals columbite and tantalite [1], which form a solid-solution series having the general composition [(Fe,Mn)(Nb,Ta) 2 O 6 ]. At present, the predominant supply of the world’s columbite–tantalite ore comes from Brazil and Australia [2]. However, columbite– tantalite occurs in many areas of Central Africa, with some 60% of the world’s Ta ore reserves located in the eastern portion of the Democratic Republic of the Congo (DRC) and adjacent areas [3]. Although the overall production of Nb and Ta in Central Africa is small at present (<1% of total global ore concentrate [2]), the illicit export and sale of columbite and tantalite from the DRC to the European and North American markets has been cited as an important means by which the civil conflicts in Central Africa are being financed [3]. A law passed in 2010 by the US Congress requires publicly traded companies in the USA that manufacture products utilizing conflict minerals, Published in the special issue Laser-Induced Breakdown Spectroscopy with Guest Editors Jagdish P. Singh, Jose Almirall, Mohamad Sabsabi, and Andrzej Miziolek. R. S. Harmon Environmental Sciences Division, ARL Army Research Office, Durham, NC 27709, USA K. M. Shughrue : R. R. Hark (*) Department of Chemistry, Juniata College, Huntingdon, PA 16652, USA e-mail: hark@juniata.edu J. J. Remus Department of Electrical and Computer Engineering, Clarkson University, Potsdam, NY 13699, USA M. A. Wise Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20013, USA L. J. East Applied Spectra, Inc., Fremont, CA 94538, USA Anal Bioanal Chem (2011) 400:3377–3382 DOI 10.1007/s00216-011-5015-2