Elemental Assay in Mining Explained
Working out the volume and quality of deposits is one of the biggest challenges prospectors and mine operators need to overcome. Assay techniques can help with this, allowing the concentration of valuable minerals and metals to be calculated.
Assay in mining also has important financial implications, providing crucial insight into the economic viability of a project and the investment potential for an operator.
Here we take a closer look at what assay is and the role it plays within the mining industry. We also explore the different techniques that can be used and share our advice on selecting the right tool for your assay needs.
What is Assay in Mining?
Assay is an analytical process that determines the composition of a substance and the concentration of specific elements. In addition to its use within the mining industry, it also has medical, chemical, and environmental applications.
Assay results are also sought out by finance and investment professionals to help determine the potential performance of businesses operating in these spaces.
How Assay Techniques Support Mining Activities
As the data they produce informs a wide range of important decisions, assay techniques are used throughout the mining life cycle.
Assay During Exploration
The initial stages of any mining project are all about finding deposits and confirming the economic viability of their retrieval. To make this calculation, operators need an understanding of the size of the deposit (tonnage), quality of materials (grade), and operating costs (mining method and ease of processing).
At this stage, assay techniques are used to help determine the potential value of the mineral or ore body. They do this by providing data on the quality and quantity of materials present in a chosen site. This information is then used to model the deposit, including the likely tonnage and grade.
Assay techniques are equally important to both greenfield and brownfield exploration activities.
Assay During Operation
Once mining activity has begun, assay techniques continue to be important.
The composition of mined material needs to be closely monitored, as it informs the optimal processing method. Significant changes in composition can also impact the planning of future mining activities, so need to be identified early.
Ongoing measurement of the concentration of target elements is also required to determine the actual value being realised from mining activities. This informs the calculation of operational efficiency and discussions around the financial viability of the mine.
Assay in Support of Environmental Compliance
All mining operations need to adhere to a range of regulations and guidelines designed to minimise environmental impacts, among other things. These include strict controls regarding the management of pollutants and contaminants.
Assay techniques allow mining operators to monitor soil and water quality to ensure it meets the required standards. Regular testing also supports the early identification of potential issues (like runoff), allowing them to be rectified or managed before they cause significant damage.
Common Elemental Assay Techniques
There are three main techniques used for assay in mining, each with its own strengths and considerations.
Pyrometallurgical Assay
This technique and has been used for thousands of years. It uses heat to extract raw materials from a sample, which can then be weighed to determine concentration. Traditionally performed using fire, modern methods use high-temperature lab furnaces to process gold, silver, and most platinum group metals.
While the exact process varies depending on the target element, this technique usually involves:
- Crushing and grinding a sample into a fine powder
- Adding dry powder chemicals – usually a fluxing agent and alloying material
- Placing the material in a cupel – a small bowl made out of a refractory material like magnesite or bone ash
- Heating the sample until it forms a glass-like slag
- Allowing the material to cool and separate – the non-precious elements will either oxidise or be absorbed into the cupel
This produces a small bead, known as a prill, which is made up of all the precious metal present in the original sample. The concentration of the target element is then calculated by weighing the prill and comparing it to the weight of the initial sample.
How Viable is Pyrometallurgical Assay?
Compared to other methods, this technique can be quite complex, time-consuming, and expensive, particularly when multiple samples need to be processed. The manual nature of multiple steps and the destructiveness of the treatment also means that the accuracy of results can vary.
Atomic Absorption Spectroscopy (AAS)
This is one of the oldest, commercially-developed analysis techniques, with the modern version largely refined by Australian scientists in the 1950s. It is based on the principle that specific atoms absorb light at unique wavelengths, and that the amount of light absorbed indicates the concentration.
For this technique, a sample usually needs to be dissolved in a liquid solution. While some AAS methods can be used on solid materials, these usually need to be crushed and ground into a fine powder first. Samples also need to be atomised, which is generally done using a flame or graphite tube.
Once atomised, samples are then irradiated, either by an element-specific line or continuum radiation source. The amount of light absorbed by the sample is measured and the concentration of the target element is determined.
How Viable is Atomic Absorption Spectroscopy?
As a specialised instrument is used to complete most of the steps, this process is fairly simple and reliable. That said, the requirement for initial preparation of the sample creates the potential for inconsistency in results.
X-Ray Fluorescence (XRF) Analysis
This technique has increased in popularity in recent years, following significant developments in analysis technology. It shares several similarities with AAS, including using unique “fingerprints” to measure the concentration of specific elements.
XRF analysers determine the chemistry of a sample by measuring the fluorescent or secondary X-ray emitted when excited by a primary X-ray source.
This dislodges an electron from the atom’s inner shell. As the irradiated atom regains stability, an electron from the higher orbital shell will replace the dislodged electron, emitting an X-ray in the process which can be measured to provide insight about the element the atom belongs to, including positive identification and characteristics.
Every element present in a sample produces a unique set of characteristic fluorescent X-rays (the fingerprint), which is why XRF spectroscopy is often used for qualitative and quantitative analysis of material composition.
How Viable is X-Ray Fluorescence Analysis?
This technique provides a few important benefits that the other techniques can’t match:
- Portable and easy to complete – analysis can be done on-site using handheld devices
- Fast results can be delivered in seconds without lengthy sample preparation or lab turnaround times
- Non-destructive and can be completed on solid samples
- Enables simultaneous detection of multiple elements
- Lower detection limits mean it can be used to identify and quantify the presence of Rare Earth Elements and Lithium Pathfinders
Choosing the Right Tool – Introducing the XL5 Plus
The unique benefits of XRF make this technique a standout for a wide range of elemental assay requirements. The Niton XL5 Plus is the premier instrument for performing fast, reliable XRF analysis.
The lightweight, ergonomic design of this handheld device makes it perfect for use on-site. Its easy-to-use navigation can be customised to suit a variety of applications, from mineral exploration to supporting mining operations. It is also powerful enough to detect:
- Metals
- Alloys
- Trace elements
- Geochemical data
- The elemental composition of powders, oils, sludge, and slurries
If you are interested in getting your hands on this invaluable bit of gear, contact the Portable Analytical Solutions (PAS) team today.
Not ready to commit to purchasing? We also offer a range of devices for rent.
Our rental equipment is fully licensed, maintained by Australia’s only factory-trained and certified engineers, and suitable for assay in mining.
Our experienced team is also available throughout the rental period to provide testing advice and technical and application support.
