Science Blog: Portable XRF as an example of advanced on-site analysis methods in mineral exploration
In this new GTK’s Science Blog text Dr. Pertti Sarala tells about the applications and experiences with portable XRF in mineral exploration in Northern Finland. The topic represents the GTK’s strategic focus areas of Mineral Economy, Cleantech, and Digitalization.
Recent methodological development has given new possibilities to determine the chemical and mineralogical composition of sample materials with accuracy and quicker than before. Advanced portable field techniques provide a cost-effective way to analyse several types of samples directly in the field and increase the number of methods to be used in exploration. These methods provide an opportunity for rapid analyses directly on site, which lowers the analysis costs, decreases the environmental impact of mineral exploration and increases sample efficiency.
One of the advanced methods is portable X-ray fluorescence (pXRF). There are several commercial hand-held and mobile analysers whose development from rough waste metal detectors to sophisticated analysers with low detection limits for a large group of elements has been huge. This makes them applicable for mineral exploration using not only bedrock and boulder samples, but also soil and glacial till. Till, in particular, has proven to be an excellent medium for pXRF analyses, as was reported in a new scientific article published by Sarala (2016) in the journal Geochemistry: Exploration, Environment, Analysis.
In the article, Sarala describes the results of a comparison of three portable X-ray fluorescence (pXRF) methods in an exploration programme using till at Sinoselkä, Kittilä, Northern Finland. The use of one truck-mounted XRF unit and two handheld pXRF analysers was tested for basal till samples gathered using percussion drilling as a part of a gold exploration project in central Lapland. The datasets were compared with both conventional aqua regia based analyses and with each other. The results proved that till is an excellent medium for pXRF due to the homogenised matrix and glacigenic distribution. Even natural, unprocessed samples can be used for pXRF analysis, and the correlation between the methods was very good for some major (Ca, Fe) and minor elements (As, Co, Cr, Cu, Mn, Ni, Pb, Ti, V, Zn). In addition, the correlation of the pXRF analyses and aqua regia digest-based results is also good, which supports the results of other testing in the Pelkosenniemi-Savukoski area, in the eastern part of northern Finland (Sarala et al. 2015). This increases the usability of pXRF datasets beside conventional aqua regia-based till geochemistry, which is and has been largely used in mineral exploration since the 1970s.
Recent studies performed by the Geological Survey of Finland prove that pXRF applications are reliable and effective methods in till geochemical exploration, particularly for relative concentrations. pXRF is a useful analysis method that can be directly used in the field to guide till sampling and further drilling. Furthermore, as in the use of any other till geochemical methods, the concentrations of pathfinder elements and indicators of secondary haloes around the ore bodies can be traced up-ice using pXRF in the field. The results also encourage the testing of pXRF analysers in other applications, such as in geological and geochemical mapping (e.g. baseline and urban geochemical mapping), environmental monitoring and research on mine districts and polluted land areas.
Hatakka, T., Nuottimäki, K., Sarala, P., Taivalkoski, A. & Tarvainen, T. 2016. Kenttä-XRF-analysaattorin soveltuvuus geokemiallisiin taustapitoisuustutkimuksiin. Geological Survey of Finland, Report 97/2015, 112 p. + 3 app.
Text: Pertti Sarala
Pertti Sarala, Ph.D., (born 1970) is specialized in applied Quaternary surficial geology and geochemistry in ore exploration. Sarala graduated in 1994 with an M.Sc. in surficial geochemical exploration and earned his Ph.D. from the University of Oulu in 2005. He has worked as a docent (Adjunct Professor) of Quaternary and surficial geology at the University of Oulu since 2009. Presently, he works as a joint Research Professor of geochemical exploration at the Geological Survey of Finland (GTK) and the Mining School of the University of Oulu, including research project generation, teaching, supervision of student graduate works and international collaboration. He is a specialist in Quaternary and surficial geological research and the development of geochemical exploration methods. In the latest projects, his focus has been on advanced, low-impact geochemical exploration techniques that leave minor traces in the environment and are therefore suitable for northern regions. He has authored about 40 papers and more than 150 other publications, including books, conference abstracts and working reports.