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Gold mines and gold deposits are often categorized by the average proportion of gold contained in the ore at the site. This is also known as the ore grade.
While higher-quality mines have higher ore grades, lower-quality mines have lower grades. When gold ore has a high grade, it takes relatively less effort to extract an ounce of gold from the ground and, since less ore has to be dug out, it reduces the input costs for the gold mining company.
Key Takeaways
- All precious metals are graded by the amount of metal within the ore.
- A higher grade means that it takes less effort to remove the metal from the ground.
- Gold is rated based on ore density measured by grams per tonne, or g/t.
- Many of the world’s highest-grade mines are in the U.S., Russian, and Peru.
Understanding Gold Grading
All precious metals are graded by the proportion of metal in the ore. Grams per tonne of milled ore, or g/t, is the most common metric used to represent the grade of ore. The value of a precious metals mine is determined by its total estimated weight, the grade of the ore, and how difficult it is to extract and distribute.
Precious metals are found in a wide range of geological sites. They show up in open pits, underground, under bodies of water, and in single nuggets resting on the ground. Grading is usually only applied to open pits and underground deposits.
Gold Mine Grading
A high-quality underground mine is described as having a gold ore density between 8 and 10 g/t, while a low-quality underground mine has a gold ore density of 1 to 4 g/t. Open-pit mines tend to have a lower grade, but they can be considered very valuable because of the lower average operating costs necessary to obtain them. It is typically recommended to use cost per ounce, and not gold ore grading, to evaluate a gold mine.
Using the g/t standard, many of the world’s high-grade gold mines are in the United States, Russian, and Peru. The Fire Creek mine in Battle Mountain, Nev., for example, was reported to have one of the highest at 44.1 g/t. Others making the list include the Macassa mine in Canada, the Kedrovka mine in Russia, and the Toguraci mine in Indonesia.
How Is Gold Purity Rated in Karats?
The purity of finished gold (e.g., jewelry) is often related in karats. A karat represents 1/24th unit of the metals present in the alloy. 24-karat gold is therefore the purest (all 24 units are composed of gold), which is rated as 99.5% or higher pure gold. 18K gold, on the other hand, would be 75% gold and 25% other alloy metals like tin or copper.
What Are the Biggest Gold Producing Nations?
Historically, most of the gold mined has come from China, Australia, South Africa, and the United States.
How Much Gold Has Even Been Discovered?
All the gold that has ever been mined, plus proven discovered reserves, amount to around 244,000 metric tons of the metal. If all of that were melted down and fashioned into a cube, it would be 28 meters (92 feet) per side, which could fit inside an Olympic-sized swimming pool.