Drill core scanning to support exploration and mining

Drill core scanning is slowly establishing itself as an analysis method among others. There are several methods provided by different service providers and system manufacturers in the market. Perhaps the best-known methods for scanning drill cores in Finland are hyperspectral imaging, LIBS and XRF scanning. In addition to mineralogy and/or chemical composition, almost all commercial solutions have the option to take high-resolution photos of drill cores. 

The advantage of LIBS (Laser Induced Breakdown Spectroscopy) over other methods is that it provides both elemental and mineralogical composition at the same time, which reduces the need for laboratory analyses, especially in mines. This method involves directing focused laser pulses onto the rock surface, generating micro plasma which emits light. The emitted light is then analyzed using a series of spectrometers. Each chemical element is identified by its characteristic spectral peaks within the wavelength range of 200 to 1000 nm, allowing for accurate determination of elemental concentration clusters. Based on the elemental composition at each measurement point, the corresponding mineral is computationally identified. LIBS differs from e.g. XRF so that it can be used to determine light elements such as lithium (Li).  Lumo Analytics device performs up to 1000 measurements per second, and the typical resolution is about 100,000 measurement points per meter. Even a lower resolution is sufficient for reliable numerical examination, but by increasing the number of measurement points, impressive visualizations can be obtained and comparisons with other chemical analysis methods become easier.  

Lumo Analytics’ LIBS based drill core scanner is easy to move and it can be integrated into the logging process. The scanning speed is 150-300m per day, meaning that the device can easily keep pace with the drilling rig, so as the cores are brought into the logging facilities, they can be scanned before logging. At best, such an approach may even lead to the drill hole being closed earlier than planned and the rig moved elsewhere, as the mineralogy tells already at early stage that mineralization will not be found or that the mineralization has already been passed.  

LIBS is one of the few, if not the only method, that can quickly and reliably measure the lithium content of rocks. It has been successfully used in lithium exploration. When laboratory analyses indicate the lithium content of whole rock samples, core scanning helps to find out the minerals where lithium is bound. Knowledge of mineralogy is essential when carrying out enrichment tests, but it is often difficult to distinguish between different minerals, especially in light colored rock. Once the cores have been scanned and mineral composition is known, one can see from the mineral maps that all the light grains are not spodumene, but some other lithium bearing mineral, like montebrasite which may not be extractable.

LIBS is one of the few, if not the only method, that can quickly and reliably measure the lithium content of rocks. It has been successfully used in lithium exploration. When laboratory analyses indicate the lithium content of whole rock samples, core scanning helps to find out the minerals where lithium is bound. Knowledge of mineralogy is essential when carrying out enrichment tests, but it is often difficult to distinguish between different minerals, especially in light colored rock. Once the cores have been scanned and mineral composition is known, one can see from the mineral maps that all the light grains are not spodumene, but some other lithium bearing mineral, like montebrasite which may not be extractable.  

The same challenge exists in the geochemistry and mineralogy of very dark rocks. The number of valuable elements can be large, but they are bound to minerals from which they are either very difficult or even impossible to extract.  LIBS can also be used to distinguish between different sulphide phases. This helps in ore modeling. When different ore types can be identified almost in real time, the mill feed can be optimized in almost real time, which means that less unwanted material is comminuted, which leads to cost savings. In addition, knowledge of feed mineralogy helps to predict the durability of consumables at the mill. 

When the elemental composition, mineral composition and grain size of the cores are known, it is possible to assess the environmental impacts of their extraction and enrichment or, for example, the utilization possibilities of waste rock.   

LIBS is already more than 60 years old as a technology, but it is only the increase in computing power that has enabled rapid analysis, and thus its use has also begun to become more common in the mining industry. Another advantage of the technology is its affordable price compared to other analyzers. At its best, drill core scanning makes the work of geologists easier by making logging more efficient and standardized. As a result, everyone understands the geology better, which helps in decision-making at different levels and stages of the project. 

This article was originally published in Finnish in Materia 2/25