Laser-induced breakdown spectroscopy (LIBS); Gold ore; Gold; Silver; Conditional analysis;INSTRUMENTAL NEUTRON-ACTIVATION; RAY-FLUORESCENCE ANALYSIS; LA-ICP-MS; INDUCED PLASMA; QUANTITATIVE-ANALYSIS; PRECIOUS METALS; SULFIDE ORES; SPECTROMETRY; ABLATION; PYRITE

The performance of laser-induced breakdown spectroscopy (LIBS) to identify and quantify gold and silver in ore samples was evaluated. Ores from a gold-producing mine and samples artificially doped with Au and Ag solutions to previously defined concentrations (surrogates) were prepared as 50-mm pellets prior to LIBS analysis. Silver detection and intensity measurement was straightforward for concentrations from 0.4 to 43 mu g/g and from 1.1 to 375 mu/g in ore and surrogate samples, respectively. Au emission lines were not found after ensemble averageor accumulation of 100-single shot LIBS spectra of ore samples containing up to 9.5 mu/g Au. However, the Au signal was present in the spectra of surrogate samples, for which a detection limit of about 0.8 mu g/g was determined. When the number of sampling shots in ore samples increased, various single shot spectra registered Au emission lines. The number of spectra containing Au emission lines increased with the number of single shots. Those results, as well as scanning electron microscopy analysis of ore samples, suggest that the discrete analyte distribution as well as the inherent discrete characteristics associated to LIBS made the presence of gold in the LIBS spark an unlikely occurrence. The particle sampling rates (the percentage of laser pulses expected to sample at least one particle) were estimated for gold concentrations of 1.1 and 10.0 mu/g as 0.04% and 0.32%, respectively. A Monte Carlo simulation indicated that >100 gold-containing particles should be sampled to accurately represent the discrete character of gold in the ore. Sampling 100 such particles requires >10(5) laser pulses over a single pellet. Despite the fact that this rather large number of shots makes difficult to conduct conditional analysis on pellets, for some samples that withstood 5000 shots, gold quantification in ores was successfully achieved at concentrations as low as 1 mu/g. Results are encouraging and illustrate the applicability of LIBS to gold and silver in field semi-quantitative analysis. (C) 2017 Elsevier B.V. All rights reserved.

SUPPORT VECTOR MACHINES; ELEMENTAL ANALYSIS; IRON-ORES; CLASSIFICATION; SPECTROMETRY; SAMPLES; PLASMA; INDUSTRY; ALLOYS; MODEL

The basicity of sintered ore, which is related to the melting point of the sinter, is vital to ore mining and blastfurnace smelting. Laser-induced breakdownspectroscopy (LIBS) with random forest regression (RFR) has been applied for measuring the basicity of sintered ore, which can be defined by the concentrations of oxides: CaO, SiO2, Al2O3 and MgO. In this work, thirty sintered ore samples are used, of which twenty samples are used for the calibration set to construct the random forest regression (RFR) calibration model for the above-mentioned oxides and ten samples are used for the test set. The characteristic lines of the main components in the sintered ore are identified using the National Institute of Standards and Technology (NIST) database. Two model parameters (the number of decision trees -ntree and the number of random variables - m(try)) of the RFR were optimized by out-of-bag (OOB) error estimation for improving the predictive accuracy of the RFR model. The RFR model was applied to sample measurements and the results were compared with partial least squares regression (PLSR) models. The RFR model has shown better predictive capabilities than the PLSR model. In order to verify the stability of the RFR model, fifty measurements were made and the relative standard deviation (RSD) of the data is between 0.27% and 0.59%. Therefore, LIBS combined with RFR could be a promising method for realtime online, rapid analysis in mining and mineral processing industries.

WATER-BASED LIQUIDS; METALLIC TRACES; LIBS EMISSION; ENHANCEMENT; IMPROVEMENT; CONFINEMENT; SENSITIVITY; PULSE; LONG

Laser-induced breakdown spectroscopy (LIBS) can benefit from sustaining laser generated plasma with microwaves to enhance elemental detection sensitivity. To achieve efficient microwave coupling, critical factors, such as the electromagnetic environment and reflection coefficient of the coupling device, need to be considered to quantitatively predict the electric-field strength in the plasma location. 3D full-wave electromagnetic simulations were used to design near-field microwave applicators suitable to maximize microwave coupling into the short-lived laser-induced plasmas. The simulations pointed out to four effective and practical designs containing varieties of isolation techniques. The four developed microwave applicators were then used to improve the detection of copper present in a mineral ore solid sample, using LIBS and imaging techniques simultaneously. It was found that, with 1.2 kW microwave power, an applicator design with a 30 mm diameter ground plane can significantly boost the signal of copper line 324.754 nm with a factor of 849, which is, to the authors' best knowledge, the highest reported value. Furthermore, an outstanding signal to noise ratio of 166 was recorded in a solid sample containing a certified 3.38 mg g(-1) copper concentration.

Portable LIBS; Micro-invasive investigation; Pyrotechnological materials; Late bronze age workshop contexts; Tiryns-Greece;PIGMENT ANALYSIS; PAINTED PLASTER; COPPER; ABLATION; IRON; ENVIRONMENT; INSTRUMENT; ARTWORKS; BRONZES; GLASSES

Laser-Induced Breakdown Spectroscopy (LIBS) was used in the investigation of pyrotechnological materials (metal and ceramic items, glass-based objects, plaster-based materials) from several Late Bronze Age workshop and activity area contexts at Tiryns, Greece. The use of a portable instrument, which could be brought into the study place where all objects were housed, was crucial in order to establish the elemental content or verify the material composition of almost all materials analysed. In almost all cases, the LIBS analyses led to the preliminary identification of the materials investigated. In most cases, the results sufficed to confirm earlier research carried out or was in agreement with similar analyses published in the literature. The analyses demonstrate that the micro-invasive LIBS technique provides useful preliminary elemental characterization of most of the pyrotechnological materials while for some, additional work needs to be conducted for securing conclusive results. Essentially, the portability and compactness of the instrumentation enable its use in any workspace with a solid desk, light and electricity access which makes this technique very attractive for obtaining preliminary elementary results. While the technique remains limited by spot analyses it does open up an immense array of possibilities for routine characterization or speedy screening of different types of artefacts in any storage or museum context. These important methodological and scientific findings are considered prerequisite steps leading towards and aiding in responsible sampling strategies for further analyses. (C) 2017 Elsevier Ltd. All rights reserved.

Laser-induced breakdown spectroscopy; miniature laser; nickel ore;QUANTITATIVE-ANALYSIS; INDUCED PLASMA; LIBS; DISCRIMINATION; CONFIGURATION; STEEL; SOIL; CU

A newly designed and developed bench-top instrument is reported for laser-induced breakdown spectroscopy offering compact size and relatively low cost. A miniature laser was designed in the laboratory with a small volume and a light weight. The spectrometer was controlled using laboratory-written software. The instrument is suitable for the direct and rapid analysis of solid samples after simple pretreatment. Good stability and accuracy were achieved for quantitative analysis. The performance of the instrument was evaluated by qualitative and quantitative analyses of nickel ore for Mn, Al, Fe, Cr, Zn, Mg, Si, and Ca. The quantitative analysis showed linear calibration graphs and small relative standard deviations. The results show that the new instrument is suitable for elemental analysis.