In contrast to modern tailings from froth flotation, little is known about historic tailings from gravity separation. However, they may be of economic interest due to their higher metal grades compared to modern tailings. As an example for these types of historic tailings, the inner structure, as well as the economic potential (Pb, Zn, Cu, Ag, Sb), of the old Bergwerkswohlfahrt mine waste dump in Germany were studied. The investigations focused on textural, geochemical, and mineralogical properties. For this purpose, an extensive drilling program was undertaken. The drill cores were subsequently analyzed with a laser-induced breakdown spectroscopy (LIBS) core scanner to obtain the detailed spatial distribution of potentially valuable elements. The fine-sized residues could be differentiated into different layers, all of them including valuable metals in varying proportions. The strong variations in stratification and in metal distribution over short distances are caused by the batch-wise deposition of the tailings. This heterogeneity within short distances has to be taken into account for future exploration of these types of deposits. The application of a core scanner using LIBS is very convenient for detailed spatial analysis of drill cores, however, the calibration effort, particularly for heterogeneous sample material, is proportionally large. The valuable metal content for Bergwerkswohlfahrt was estimated to be 8000 metric tons of Pb and 610,000 ounces of Ag. Although of limited economic value, recycling might finance future remediation costs. Furthermore, the occurrence of historic tailings in nearby clusters may present further recycling opportunities.

A new approach using scanning Laser Induced Breakdown Spectroscopy (LIBS) was developed to unravel cryptic variations in the mineral chemistry of chromite, orthopyroxene, and plagioclase in drill core from Merensky Reef and UG-2. The LIBS method provides continuous spatially resolved chemical data, elucidating variations in mineral chemistry and in element partitioning, taking into account textural features of the rock itself, of individual minerals, and of immediate neighbourhoods. Since the method is relatively fast and easy to apply to numerous core sections, it is of special interest when comparing the lateral variability of diagnostic horizons such as Merensky Reef and UG-2. This approach for measuring Mg/Fe, Cr/Al and Ca/Na ratios is based on the strength of LIBS in detecting chemical variations using intensity ratios within a single matrix, which in this application is one single particular type of mineral phase. Supervised classification followed by k-means clustering was applied to identify those spectra that consist of pure chromite, orthopyroxene, and plagioclase. Measurements and data processing strategies were focused on minimizing the standard deviation in the LIBS-based ratios to be able to detect relatively small variations in mineral chemistry. The LIBS-based Cr/Al and Mg/Fe ratios were successfully validated with respect to electron probe microanalysis on multiple polished sections. Distinct trends could indeed be extracted from a continuous LIBS measurement of 6 m drill core through the Merensky Reef. The data correlate with whole-rock geochemistry and hydrous phases such as phlogopite. The LIBS-based approach opens up unique insights into chemical and mineralogical expressions of large- and local-scale processes. This allows unique and detailed interpretations relevant for the genesis of mineralizations and metal distributions, based on a comprehensive dataset.

The EU aluminium production from, e.g., bauxite is one of the backbones to support Europe’s green and digital transition. In support of sustainable bauxite exploration and mining, Laser Induced Breakdown Spectroscopy (LIBS) was used on the major facies of the karst bauxite deposits of SODICAPEI (Southern France). Our results showed that LIBS is a very promising technology to define the bottom and top layer of bauxite ores and to access critical parameters crucial for bauxite mining and processing. First LIBS tests were made on scandium standards to find appropriate Sc emission lines for future applications.