Driving informed mining decisions using high-speed LIBS core analysis. An article by Dr. Cameron Chai, Alejandro Fayad, Rowena Duckworth and Melissa Narbey.
Laser Induced Breakdown Spectroscopy (LIBS), is now a viable technique for large-scale analysis of geological materials with the ability to contribute to ore body knowledge and directly influence exploration geology programs and process metallurgy operations. The technique has some similarities to spark OES which has been used for many years in the metals industry to confirm or identify alloy grades.
While LIBS is not a new technology, it really came to the fore in 2012 when NASA employed it on the MARS Rover Curiosity. Their LIBS system called ChemCam is mounted on top of the mast and can analyse materials as far as seven metres away, where it was used to determine the composition of Martian geology samples. In July 2021 it was reported to have collected over 800,000 spectra from more than 2,500 individual targets. In the process, it has been responsible for some of the Rover’s most significant discoveries.
Main image: The NASA Curiosity Rover. The ChemCam LIBS system is housed in the module atop the mast (photo courtesy of NASA).
In recent times, Canadian-based ELEMISSION Inc. developed the technology for similar applications with a more terrestrial focus.
How does LIBS work?
LIBS employs a high-intensity pulsed laser directed at the surface of a sample. The surface is transformed into a micro-plasma cloud consisting of atoms, ions, molecules and electrons in an excited electronic state. As these particles return to their ground state, they release energy in the form of characteristic wavelengths of light. The emitted light is collected using a highly sensitive on-board spectrometer, enabling simultaneous detection of multiple wavelengths related to a specific element or group of elements. With the intensity of the spectral lines being proportional to the elemental concentration, scientists have been able to use this to identify and quantify elements in the material under study. The right combination of laser energy, advanced calibration techniques and high-performance spectrometers allows the technique to reach great sensitivity, with detection limits that can go as low as ppb in concentration levels.
LIBS mapping compared to XRF and Infrared Hyperspectral Mapping
X-ray fluorescence (XRF) is a staple analytical technique in the mining industry, mainly used to provide elemental analyses on bulk materials. Despite XRF’s extensive use, it is insensitive to light elements such as lithium, beryllium, carbon etc. XRF’s inability to detect light elements is tied to their atomic weight, with light elements such as lithium not able to be detected due to their X-ray fluorescence being too weak to detect. LIBS on the other hand is able to detect every element in the periodic table.
An analogous technique to LIBS mapping is the fairly new micro XRF mapping. Both techniques have similar spatial resolution, however, the LIBS mapping is orders of magnitude faster and is more sensitive to more elements, providing microanalysis on a macro scale.
Infrared Hyperspectral scanning utilises light from the visible, near-infrared (NIR) and short-wave infrared (SWIR) portion of the spectrum. By measuring the reflected light across numerous narrow and contiguous spectral bands, the scanner can capture the distinct absorption features of various minerals. These features have their own absorption pattern and algorithms can be used to deconvolute spectra to reveal the nature of the minerals within a drill core. While hyperspectral measurement scanners can capture data very quickly, they are best used for identifying fine-grained sheet silicate alteration minerals rather than overall mineralogy and textures.
In comparison to other core scanning technologies:
| LIBS mapping | µXRF | IR Hyperspectral | |
| Sample preparation | None | None | None |
| Measurement time | Very fast | Slow | Extremely fast |
| Outputs | Elements and minerals | Elements and minerals | Minerals only |
| Elemental range | Entire periodic table | Na to U | – |
| Limits of detection | Low ppm to ppb | Low ppm | ~ 5% |
| Resolution | 30µm | 5-50µm | 250µm |
LIBS generates a spectrum from every spot scanned. By scanning many spots, typically many thousands, a detailed analysis of the sample can be generated, extending from elemental composition (similar to XRF), through to quantitative mineralogy.
ECORE Rapid LIBS core scanner
ELEMISSION, which has been developing LIBS-based systems for geochemistry since 2014, recently launched the ECORE, a revolutionary laser-based core scanner designed for fast and efficient scanning of drill core and other geological materials. Using technology refined in the ECORE Flex that is currently being used by the CSIRO, the ECORE offers automated workflows enabling core samples to be analysed at a rate of up to 1000m/day.
The first commercial ECORE installation has recently taken place the Automated Mineralogy Incubator (AMI) in Perth where it is at home with other automated mineralogy systems. At the AMI, this cutting-edge analytical tool is available for use by the mining industry where clients can also benefit from the expertise of the AMI’s in-house mineralogists.
Using drill core and rock chips loaded into core trays, the ECORE provides ultra-fast automated mineralogy with the aid of artificial intelligence. The system scans 30µm spots at variable resolutions (i.e. distances between spots), typically in the range 50 to 1000µm, with larger spacings possible if required. Core is usually scanned strip-wise, analysing a section down the length of the sample with a width of up to 40mm. At a standard sampling rate of 1300 spots per second and a one cm strip width, a full tray can be scanned in about 20 minutes at low resolution, while specific areas of interest can be identified and scanned at higher resolution if desired. This type of analysis generates highly detailed analyses that can be completed within a matter of minutes, with data available shortly after scanning.
Traditionally, core samples are logged by geologists who have learned to identify minerals with the naked eye, but this is highly subjective and depends on the geologist’s skill. Often minerals that are quite different in composition are very similar in colour, density and texture. Additionally, there are microstructures relating to the rock formation that are not obvious to the naked eye or even under a hand lens. Complications in the natural world also extend to variations in chemistry in minerals that cannot even be determined by optical techniques.
Case study
The Geological Survey of Western Australia (GSWA) has a mandate to provide the most detailed geological information possible to aid mineral exploration and the mining industry in Western Australia. They have an extensive core library containing donated core and core that has been co-funded between exploration companies and the Government of Western Australia. Below is data from the co-funded Exploration Incentive Scheme (EIS) and Pilbara Minerals from the Pilgangoora area of Port Hedland in WA.
The ECORE has a camera that not only helps it to navigate the samples, but also provides valuable optical images that provide the basis for the chemical and mineralogical data to be overlayed. A skilled geologist could probably look at these core samples and identify the presence of phases such spodumene, K-feldspar, quartz etc., but quantifying how much is there, and identifying trace phases is much more difficult to determine.
The image below shows a full tray of drill core and overlayed is the elemental strip map for lithium. These samples were scanned using 50µm spots at high resolution i.e., 100µm spacings, with the entire tray taking about 90 minutes to scan. The scan time could be reduced by increasing the spot spacings.
There are clear zones of high lithium concentration throughout each core sample indicating areas of potential commercial value. Of interest are the zones of high lithium content where the mafic zone intersects the pegmatite and host rock.
As each element has a unique spectral fingerprint, the spectra from a multi-element material can be deconvoluted by looking at specific peaks from individual elements and hence the elemental composition derived. The image below shows element maps for the elements Li, Cs, Rb, Be, Na, and K, with the dark red regions containing the highest concentration and dark blue the least concentration of each element, calculated on a pixel-by-pixel basis. In this case, it is easy to see the presence of lithium with some regions containing noticeable quantities of Cs and Rb, which is consistent with Li-bearing micas. The provided logs indicated significant spodumene content, so the high lithium content observed was expected. However, the logs did not provide any quantification, which can be easily achieved using the ECORE.
Image: Element maps for key elements of interest for a spodumene-bearing core sample.
While elemental analyses are important, and the presence of high lithium content extremely promising, the ECORE can also generate automated mineralogical maps and determine quantitative mineralogy. This is achieved using the entire spectral fingerprint of all of the elements present. The resultant data can be of great interest to exploration geologists and mining engineers.
The ECORE mineralogy image below shows the mineral maps generated by the ECORE software. These maps clearly show which minerals are present, and where. Spodumene-rich regions are evident (green zones) in close association with K-feldspar and quartz, which is to be expected from this type of deposit. Interestingly, a small amount of lithium-bearing bityite is also observed which could be easily overlooked during a visual inspection.
Summary
The mining industry has to embrace the latest technologies to both remain competitive and also utilise best practices to positively influence their decision-making processes. The decision-making processes need to be driven by definitive data. The ELEMISSION ECORE is able to provide reliable data at a rate that is commercially relevant and can be used to target mining exploration projects or optimise process metallurgical operations.
Especially suited to lithium-bearing minerals such as spodumene or lepidolite that are outside the realms of XRF, the ELEMISSION ECORE LIBS scanning excels with its ability to directly detect and quantify lithium minerals. By analysing millions of micro-sized points along the length of core samples, the ECORE is able to provide elemental and mineral maps. In addition, the ECORE has demonstrated its value to the mining industry with the ability to rapidly analyse large quantities of drill core without subjectivity. Geologists will have time for data interpretation rather than spending their time manually acquiring the data. Access to this technology is now available at the Automated Mineralogy Incubator in Perth.