CHEMICAL MAPPING WITH LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

Compositional maps of small geologic samples produced by scanning electron microscopy (SEM) are a common geochemical tool to understand both the distribution of elements and the causal processes. However, SEM samples are limited in size; samples must be collected from the outcrop, cut to size, and analyzed in vacuum in the laboratory. Laser-Induced Breakdown Spectroscopy (LIBS) is an rapid analytical technique that can produce compositional maps of samples of any size, in the laboratory or in the field.

LIBS uses a high-power focused laser to ablate the surface of a sample; the atoms are excited in the resulting high-temperature plasma. The light emitted as electrons decay from excited orbitals is collected by fiber optic or telescope, diffracted, and recorded on a CCD camera. Results are obtained in seconds and sample preparation is minimal. Spot size, which limits spatial resolution, is typically 20-100 microns in diameter.

The speed and flexibility of LIBS permits the production of chemical maps at many scales in a short time frame. Such maps would be useful in any chemically heterogeneous rock; many LIBS maps could be made in the field, providing context for samples taken for further study in the laboratory. Transects across significant features can be imaged for chemical gradients without the need to collect and analyze numerous samples.

Chemical mapping with LIBS has been conducted on a copper ore sample from Butte, MT. Samples of marbles from Oro Grande and Organ, New Mexico, have been prepared to further illustrate the capability of this mapping technique.