Assay

What Is an Assay?

An assay is a process of analyzing a substance to determine its composition or quality. The term is often used in the mining industry to refer to tests of ore or minerals. The term assay is also used in the environmental, chemical, and pharmaceutical industries.

Assaying is also important in futures markets. Metals that are used to meet delivery requirements of futures contracts must be assayed to ensure that they meet the stringent quality and purity requirements mandated by the futures exchange for the particular contract in which that metal is traded. The existence of the physical delivery of metals helps in the convergence of prices between futures and spot markets.

Key Takeaways

  • An assay is a process of analyzing a substance to determine its composition or quality.
  • Three techniques - fire assay, wet chemistry, and instrumental analysis - are primarily used to analyze and determine purity of metals.
  • Assays are used in futures markets to meet delivery requirements for metal futures, as specified by exchanges.
  • Assays in medicine assist in the development of new drugs and vaccines.

Understanding Assays

Assay results provide an early indication of the potential value of a mineral or ore body, and therefore they are closely monitored by investors in mining companies. An exceptional assay result can trigger a sudden sharp rally in the stock of a company that holds the mineral rights of the property. Conversely, poor assay results may lead to a significant decline in a stock that has run up on speculation about promising results.

In medicine, an assay is an analysis used to determine the presence of a particular substance and its concentration. Thus, for example, an assay may be conducted on a vaccine, to determine its effectiveness or potency in preventing illness. There are several types of medical assays. In addition to the potency and presence assays already mentioned, medicine uses a number of assays for determining the effectiveness of the immune system, exposure to certain viruses including AIDS, detecting certain sexually transmitted diseases, and working with thyoid hormones.

Chemical assays analyze the quality of raw materials. Organic chemicals, for example, are assayed using gas chromatography and infrared spectroscopy. Raw materials in manufacturing may be assayed using titration or gravimetric analysis. Generally, these seek to determine the quantity of a constituent in a sample. Titration does so, for instance, by adding another substance to which the sought substance is known to react in a specific way.

In medicine and in chemistry, assays can be either biochemical or cell-based procedures. The choice between the two is usually a matter of choice for the individual conducting the assay. Cell-based essays, however, not only obtain potencies, but also can detect certain toxicities and effects on growth as well. Recently, cell-based assays have had more success in identifying new kinds of drugs.

The information gleaned from assays can impact financial markets in various ways. A mining company whose latest assay indicates large quantities of high-grade ore will see its stock price escalation sharply. Medical assays showing the likely development of a new drug therapy or vaccine can be equally positive on the stock price of a pharmacology company. Assays of every kind provide the market will valuable and generally highly accurate information on which to base purchase and sale decisions.

In medicine and in chemistry, assays can be either biochemical or cell-based procedures. The choice between the two is usually a matter of choice for the individual conducting the assay. Cell-based essays, however, not only obtain potencies, but also can detect certain toxicities and effects on growth as well. Recently, cell-based assays have had more success in identifying new kinds of drugs.

The information gleaned from assays can impact financial markets in various ways. A mining company whose latest assay indicates large quantities of high-grade ore will see its stock price escalation sharply. Medical assays showing the likely development of a new drug therapy or vaccine can be equally positive on the stock price of a pharmacology company. Assays of every kind provide the market will valuable and generally highly accurate information on which to base purchase and sale decisions.

Types of Assay Techniques

There are three main techniques used to assay minerals: fire assay, wet chemistry, and instrumental analysis.

The fire or pyrometallugical assay method is the most popular method and consists of grinding samples into a fine powder which is mixed with dry powder chemicals. Some samples are first tested by X-ray flourescene to roughly determine the composition of the sample. The sample is weighed before the dry chemicals are added.

Subsequently, the samples are heated in a ceramic or metal container, which decomposes the sample intoa glass-like slag. Chemical reactions then turn the sample into an alloy. Once this happens, the sample is poured into a mold to cool. its constituents. A shallow cup is used to separate out the mixture further and the metals are then analyzed using instrumental analysis technique. The mixture is then transferred to a shallow cup made of phosphorous, bone ash, or calcium phosphate. The fire assay takes place leaving behind a small bead of precious metal.

Distillation,dissolution, titration, and gravimetric analysis, similar to precipitation, are used in the wet chemistry analysis method. In this method, the sample is dissolved in a solution so that the solution can be analyzed. Wet assay takes more steps than fire assay, but it is also more accurate. The characteristics of the sample due to the chemical reaction with the titrant. It can be detected either by a color change or a sensor.

Titration is a quantitative chemical analysis that adds a solution (the titrant) to the sample hat is to be analyzed. The titrant will contain a known concentration of a chemical that reacts with the substance for which the assay is being done.

Gravimetric analysis is the most commonly used wet method. The material is precipitated, filtered, washing, dried, and weighed to determine mass. The mass is the compared to a determined mass to identify the percentage of metal present.

Assay in the Futures Market

The vast majority of futures contracts are liquidated before their designated delivery date. Ususally, less than 5 percent of futures market contracts make or take delivery of the underlying commodity. That being said, futures markets rules will set specifications for acceptable or "deliverable" precious metals, that is, metal that meet the exchange's rules for acceptable delivery.

On futures markets, precious metal are traded in bars. The primary markets for precious metal are in London and in the CME Group's markets in the United States. Bars acceptable for delivery (i.e., deliverable bars) range in size from as much as 1,000 troy ounces for some silver bars to 100 troy ounces. Some bars are measured in kilograms and taels (a Chinese unit of measure for precious metals usually set at 50 grams.

Anyone who takes direct ownership of precious metals, as opposed to receiving warehouse certificates indicating that the bars owned by that individual are held at that warehouse, has to take certain steps with the metal. Arrangements must be made of custody, secure transportation, and insurance. If the metal leaves the custody of an approved entity, it will need to be re-assayed before it can go back into the futures markets as deliverable.

Futures exchanges typically specify the metal's quality for delivery in the contract market rules for that metal. For example, the CME Group, which lists gold futures listed on its trading platform, requires a minimum fineness of the metal of 995, or 995 parts per thousand, for delivery in the COMEX gold futures. For platinum, the minimum fineness is 99.95%.

Exchange rules provide the quality of the metal which will be deliverable, the methods acceptable for delivery, the assayers whose certificates of purity will be acceptable, and the precious metal depositories where deliverable metals may be held.

CME rules provide that precious metals can be delivered in only three ways, one of which is "directly from an approved assayer with the assay certificates." The CME provides a list of approval assayers for its members and persons trading on the Exchange. Only precious metals of certain brands or meeting certain conditions, specified in the rules, or assayed by an approved assayer and accompanied by that assayer's certificate, are deliverable on the exchange.

Real-World Examples of Assay

Assay results can move prices for mining and exploration companies. The movement results from the potential for future product demand and earnings growth, or a reduction in the same from poor assay results. For example, in 2020, Thor mining, an Australian mining company, saw its stock price rise after it reported that high grade gold sediments had been found at its Pilbara Goldfield Ragged Range project in Western Australia. Some of the gold was reported to be of grades higher than two grams per tonne. Further testing showed four distinct clusters of consistently high grade gold. Its stock price also rose following the confirmation of discovery of high-grade tungsten at another project.

In another example, familiar to anyone living anywhere in the last two years, is the critical contribution of fast and robust bioanalytical assays in the development of the COVID-19 vaccine. Assays specific to SARS-VoV-2 were developed and allowed for the rapid analysis and ongoing development of the COVID-19 vaccine. Among those used were viral detection and viral load assays, used to develop control groups and for setting a baseline in analyzing viral load. Antibody assays were developed and used to assay the effectiveness of prototype vaccines. Antibody assays, while useful for working with vaccine development, are not intended for use by themselves as dianostic tools. Vaccine antigen and antibody assays helped to determine how effective a given prototype vaccine was. These assays often allow for detecting antibodies early.

Frequently Asked Questions

What Is Assay in Testing?

An assay in a lab setting is an investigative procedure for qualitatively or quantitatively measuring the presence, amount, or function activity of a target element. It is used in medicine, mining, pharmacology, various forms of biology. The target element is called the analyte, measurand, or target. The assay looks to measure the target's intensive property and express it as a relevant measurement.

What Is an Assay in Biology?

An bioassay determines the relative strength of a sample compound to a standard compound. It compare the effect of the sample on a test organism as compared to a control standard preparation. It seeks to find the concentration or purity of a substance such as vitamins, hormones, or growth factors by measuring their effects on tissues, cells, enymes, or other receptors.

Generally, the response of the live material is judged at several different dose levels. A classic old "bioassay" was the canary in the coal mine. Canaries were more sensitive to the build-up of methane and would die when exposed to excessive amounts. The dead canary was a signal to the miners that there was too much methane in the mine, and they should leave it as quickly as they could. While not good for the canary, the test was a lifesaver for miners in the pre-industrial period.

What Is an Assay Value?

An assay value is the quantity of an ore's valuable elements, calculated by multiplying its assay grade or percentage of valuable elements by its dimensions. For precious metals, this figure is generally set out in troy ounces per ton of or or assay ton. Assay value can also refer to the monetary value of an orebody, determined by multiplying the amount of its valuable constituents by the market price of the precious metal.

What Is a Gold Assay?

A gold assay is a process to measure the purity of items containing gold. It helps to ensure that gold coins or bullion bars produced by a mint meet the correct purity and content standards. There are two common assaying methods.

Fire Gold Assaying is the is one of the oldest and most accurate ways to check the gold purity of an item. It is time consuming, taking about five hours to comoplete.

X-Ray Fluorescene Gold Assaying (XRF Gold Assay) is a process in which gold is irradiated by X-rays. The assaying judges the metal's purity by the intensity leve of the X-ray emitted by the sample. This is a fast and non-destructive methods of testing the gold purity of the exterior of an object. It does not, however, perform well against deep tungsten inserts in bullion bars.

Once a gold assay has been completed, either the owner will receive an assay certificate giving the authenticity of the metal or the bar will have an official assay proof stand on the bar.

One of the oldest gold assays still being performed annually is the Trial of the Pyx, a judicial ceremony in the United Kingdom ensuring that newly minted coins from the Royal Mint conform to the required size and fineness specifications.

Article Sources
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  1. CME Group. "What is the Precious Metals Delivery Process?"

  2. Reuters. "Thor Mining Plc."

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