Fire assaying is an analytical technique used in the determination of the quality and purity of gold. This method dates back to ancient times but has been refined and improved upon over the years. It involves the use of heat to melt a sample of gold and separate it into its purest components.
The process of fire assaying begins with a sample of gold being mixed with a flux, a material that helps to purify the metal. The flux contains borax, soda ash, and silica, and is heated in a crucible to a high temperature. The gold sample is then added to the mixture and heated until it melts. As the gold melts, other impurities such as base metals and other non-gold materials are oxidized and react with the flux to form a slag.
The molten gold is then poured into a mould to cool and solidify. The resulting metal bar is usually inspected for quality and characteristics such as colour, density, and texture. The smelting and refining process may need to be repeated a few times to ensure that the gold is pure.
Once the gold has been purified, it is weighed to determine its mass. The mass of the gold is then calculated based on the weight of the entire sample. This process is called the cupellation stage. This allows for a more accurate determination of the gold concentration in the original sample.
Fire assay is a reliable and accurate method of determining the purity of gold. It is widely used in the jewellery industry to ensure that the gold used is of high quality and not mixed with other metals. It is also used in the mining industry to measure the amount of gold in ore samples.
Fire assay is a time-consuming process and requires a skilled technician to perform it correctly. The process can take up to several hours to complete and involves several steps. However, the results are very accurate and reliable.
In Zimbabwe, Fidelity Gold Refinery (FGR) has the capacity to refine gold to purities of 99.5% and above using these refining techniques:
- Miller chlorination process
- Electrolytic refining process
- Aqua regia refining process
In conclusion, fire assaying in gold is a method used for the determination of the quality and purity of gold. It involves heating a sample of gold with a flux to melt it and separate it into its purest components. The molten gold is then poured into a mold and allowed to cool and solidify. The metal bar is inspected for quality before being weighed and its purity is determined. Fire assay is a reliable and accurate method used in the jewellery and mining industries to ensure the quality and purity of gold.