Integrated Laser-Induced Breakdown Spectroscopy (LIBS) and Multivariate Wavelet Tessellation: A New, Rapid Approach for Lithogeochemical Analysis and Interpretation

Fernando F Fontana,Jessica Stromberg,Yulia A Uvarova,Steven Tassios,Ben Van Der Hoek,Caroline Tiddy

doi:10.3390/min11030312

Abstract

This paper demonstrates a novel approach that uses wavelet tessellation in rapid analysis of raw geochemical data produced by laser-induced breakdown spectroscopy (LIBS) to produce pseudologs that are representative of stratigraphy. Single-line LIBS spectral data for seven major rock-forming elements (Al, Ca, Fe, Mg, Si, Na and K) were collected from a synthetic 22-sample rock-block comprising two distinct lithological groups based on mineralogy, chemistry and texture: plutonic rocks and marble. Seven sublithologies are identified within the rock-block from traditional laboratory whole-rock geochemical analysis: marble, Mg-marble, granite, quartz monzonite, foidolite, granodiorite and gabbroic diorite. Two-domain clustering (k = 2) on raw spectral LIBS data combined with wavelet tessellation was applied to generate a simplified lithological stratigraphy of marble and plutonic rocks and generate a pseudolog identical to the rock-block stratigraphy. A pseudolog generated from seven-domain clustering (k = 7) and wavelet tessellation successfully discriminated most sublithologies within the rock-block slabs, especially marble slabs. Small-scale units were identified within the more mineralogically and geochemically complex plutonic slabs. The spatial resolution of the LIBS analysis, with a measurement spacing of ~0.35 mm, allowed for assessment of individual mineral compositions and rock textures, and small-scale units within the plutonic rocks can be correlated to specific coarse-grained minerals or mineralogical associations. The application of the wavelet tessellation method to raw LIBS geochemical data offers the possibility of rapid and objective lithogeochemical analysis and interpretations which can predate further analysis (quantitative) and supplement geological logging.

Highlights

Classification and discrimination of rocks is commonly performed by geologists via visual inspection in the field during mapping or by geological logging of drill core
Assigning pseudostratigraphy for the k = 2 classification was relatively simple as plutonic rocks and marble are chemically distinct
Rapid and objective lithogeochemical analysis and interpretations can be made by applying raw laser-induced breakdown spectroscopy (LIBS) data collected on rocks to the wavelet tessellation method with classification by k-means clustering

Summary

Introduction

Classification and discrimination of rocks is commonly performed by geologists via visual inspection in the field during mapping or by geological logging of drill core. Visual interpretation of rock lithology is notoriously subjective to human interpretation (e.g., Curnamona Province: [1,2]). Significant advancements in technologies that offer generation of rapid and standardized compositional data have been realised, including new tools using laser-induced breakdown spectroscopy (LIBS; e.g., ELEMISSION Inc. Coriosity), X-ray fluorescence (XRF; e.g., Minalyzer CS® ), and hyperspectral imaging (e.g., Corescan® Hyperspectral Core Imager Mark III). The utilization of analytical devices for collection of standardized data, coupled with rapid and reliable techniques for

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Discussion

Conclusion