Laser-induced fluorescence images and Raman spectroscopy studies on rapid scanning of rock drillcore samples

Research highlights
• Minerals are identified using Raman measurement with Non-Negative Least Squares (NNLS) method.
• NNLS method is based on linear fitting of reference spectra to the sample spectrum.
• Mineral abundance is estimated using laser-induced fluorescence (LIF) image analysis.
• Larger areas of samples are scanned by dispersing and amplifying the laser beam of LIF setup.
• Combined Raman and LIF is a promising way to provide mineral maps of drillcore samples.

There exist many different ways of analysing rock drillcore samples. Here the interest is on the faster exploration activities of mining. A capable, rapid and online measurement technique is presented for analysing the mineral composition of rock drillcore samples. Raman analysis is an accurate but slow method of analysing rock drillcore samples. On the other hand, laser-induced fluorescence (LIF) can be used as a rapid method to produce a colour map of minerals based on their fluorescence. These two methods can be combined by calibrating LIF measurements with Raman results. This paper presents a combination of Raman analysis with LIF image analysis to form a rapid online mineral exploration technique used on the rock drillcore samples. To the best knowledge of the authors, the combination of LIF and Raman in the study of rock drillcore has not been published. The sample set under study is segments of rock drillcore collected from a Ni–Cu multi-metal mine situated in Kevitsa, Finland. Scanning drillcore samples using LIF technique produces images which present a map of colours based on emissions of fluorescent minerals. Some parts of the sample set, based on the exposed colours, are measured through Raman spectroscopy and the minerals are identified using reference spectra from a public source. Identification of minerals through Raman analysis is done using Non-Negative Least Squares (NNLS) method. Results show that colours of LIF images correspond to minerals identified through Raman analysis. The combination of LIF and Raman is then used to produce mineral maps of the drillcore samples and finally an estimation of the mineral abundance per units of drillcore area is developed.