Assay testing is used to determine the content of a sample. Assay testing, by definition, can be applied to any material. For example, testing a sample of blood for the presence of a drug is an assay test. As the term applies to mining, it involves testing a sample of ore for the presence of a target mineral. By determining the amount of the desired mineral present in the sample, the assay determines the value of the ore and may also suggest the proper process for extraction.
The assay testing processes varies depending on the target mineral. In some cases, where the mineral content is unknown, the ore may be tested for a number of minerals.
Assaying a ore sample for the presence of gold follows the cupellation process. Samples of ore are crushed and then heated. This concentrates the metals and separates them from the rock segments of the ore. Pure lead is added to the metal further allowing the metals to separate from the rough ore. Cupellation assaying utilizes small containers known as cupels for the crushing and heating process. The amount of gold in the assay sample is compared to the weight of the ore sample to establish a value per ton of the ore. This value is often used to determine if the mine is economically viable.
Silver ore samples are assayed using a chemical process known as titration. Ore samples are placed in an acid solution. The acidity of the solution is measured and the resulting information is used as a variable in a formula that calculates the concentrates within the sample. A variety of acids are used in the titration process. In addition, this method of assaying is used in a number of ore testing processes.
Assaying platinum ore utilizes a spectrograph process. Spectral analyzers are used in a number of testing processes including platinum. The process measures and analyzes the radiated energy emitted from the sample. This energy is often in the form of visible or invisible light. The process utilizes computerized equipment as well as high-tech monitoring systems and is among the most advanced of the assay processes.
History of Assaying
The processes of assaying are as old as the history of mining. While the technology has changed, especially in the last century, the goal is still the same. The sample is analyzed to determine its mineral content. This information is then used to establish a value to the ore and to the mine. In some cases, multiple assay methods are used not only to determine if multiple minerals are present but to confirm the assay results. The processes are scientific tests and commonly performed in certified laboratories. Commercial mine interests often require the labs to maintain confidentiality during the assaying process.
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Geoff Dixon is a freelance blogger who specializes in Mining and Technology. This article was brought to you by Coretrays.com, a leading provider of Core Trays and Core Boxes.