Accurate gold analysis is essential in mineral exploration and mining. Reliable analytical results are needed for resource estimation, mine planning, grade control and economic evaluations. However, gold is also one of the most challenging elements to analyze accurately.
Unlike many other elements, gold is rarely evenly distributed in a rock sample. It may occur as very fine particles or as visible coarse grains. Because of this, the analytical method must match both the sample type and the characteristics of the deposit. Using an unsuitable method can lead to inaccurate results and lower confidence in exploration and mining decisions.
The main challenge in gold analysis is representativity. The goal is not only to analyze the sample accurately, but also to ensure that the analyzed portion truly represents the entire sample.
The quality of gold analytical results is influenced by several factors. Coarse gold particles can cause significant variation between subsamples, while uneven gold distribution within the sample makes representativity more challenging. Larger analytical sample masses generally improve representativity, particularly for coarse-gold mineralization. In addition, proper sample preparation, including crushing, pulverizing, mixing and splitting, helps produce a more homogeneous sample and reduces sampling errors.
If coarse gold is present, the so-called nugget effect may cause significant variation between duplicate analyses. In these cases, selecting the right analytical method becomes particularly important.
Good sample preparation is the foundation of reliable gold analysis. Its purpose is to reduce particle size and produce a homogeneous sample before analysis.
The preparation procedure depends on the analytical method being used. Some methods require only crushing and splitting, while others require the sample to be finely pulverized.
Although pulverizing improves homogeneity, it is not always the best solution. In samples containing coarse gold, some particles may become trapped or smeared onto the grinding bowl, which can affect the analytical result. For this reason, the preparation method should always be selected together with the analytical method.
Different analytical methods are designed for different applications. No single method is the best choice for every sample.
PhotonAssay is a modern, non-destructive method that determines gold content using high-energy X-rays and gamma-ray detection, with no chemical digestion or fusion required. It is particularly suitable for exploration of coarse-gold deposits, grade control and rapid gold determination. The method offers fast turnaround times, high sample throughput and a more sustainable alternative to conventional fire assay. PhotonAssay will become part of the CRS Laboratories service offering in early 2027.
Fire assay has been the industry standard for gold analysis for decades. During the process, gold is separated from the sample by high-temperature fusion before being measured. It remains one of the most widely used methods for exploration and mining applications.
Screen fire assay is specifically designed for samples containing coarse gold. By separating and analyzing the coarse and fine fractions individually, the method reduces the nugget effect and provides more representative results for coarse-gold mineralization. The method is relatively expensive, so it is usually not used for large numbers of samples.
The PAL1000 method is a partial leaching technique that dissolves cyanide-soluble gold using a sodium cyanide solution. It analyzes a relatively large sample, improving representativity compared with many conventional techniques. It is particularly useful for projects where cyanide-soluble gold is the primary target.
Aqua regia digestion is a partial digestion method using a mixture of hydrochloric acid and nitric acid. The method dissolves most sulphides, carbonates and some oxides, while more resistant silicate minerals remain largely unaffected. It is commonly used for soil and till exploration, process samples and multi-element geochemical studies.
| PhotonAssay | Fire Assay | Screen Fire Assay | Cyanide Leach (PAL1000) | Aqua Regia | |
| Destructiveness | Non-destructive | Destructive | Destructive | Destructive | Destructive |
| Sample preparation | Crushing & splitting | Crushing & pulverizing | Crushing, pulverizing & sieving | Crushing & splitting | Crushing & pulverizing/ sieving |
| Sample size | 300-600g | 30-50 g | 0.5-1 kg | 0.5-1 kg | ~20 g |
| Throughput | Up to 70 samples/hour | Batch dependent | Batch dependent | Up to 52 samples/run | Batch dependent |
| Detection limit | 0.03 g/t Au | 0.002 g/t Au | 0.9 g/t Au | 0.01 g/t Au | 0.5 ppb Au |
| Partial/total | Total gold | Total gold | Total gold | Partial (cyanide leachable gold) | Partial (most minerals, excluding silicates) |
| Assay time | 2 minutes | 4-5 hours | 4-8 hours | 2-4 hours | 2-4 hours |
| Cost (compared to Fire Assay) | Comparable | Reference | ~3x | Comparable | ~1.5-2x |
| Automation | High | Low to moderate | Low | Moderate | Low |
| Sustainability | No hazardous reagents | Uses lead-based fluxes and acids | Uses lead-based fluxes and acids | Uses cyanide reagents | Uses strong mineral acids |
| Best suited for | Coarse gold | General gold analysis | Coarse gold | Cyanide-leachable gold | Geochemical exploration |
Every gold deposit is different, and the best analytical method depends on the sample type, gold mineralization and the purpose of the analysis.
For fine, evenly distributed gold, conventional fire assay may be the most suitable choice. For coarse-gold mineralization, larger sample methods such as screen fire assay, PAL1000 or PhotonAssay can significantly improve representativity and reduce uncertainty.
Reliable gold results are achieved through a combination of representative sampling, appropriate sample preparation and a fit-for-purpose analytical method. Considering these factors together helps produce analytical data that supports confident exploration and mining decisions.
CRS Laboratories offers a range of gold analytical methods to suit different sample types and project requirements, with PhotonAssay joining our service offering in early 2027. Contact our team to find the method that best fits your project.
Did you miss our webinar on gold analysis? We’re happy to send the recording to you on request!