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.
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.
- 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.
- The World Gold Council rates gold 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.
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.
The official standards of high-grade or low-grade gold ore today are set by the World Gold Council, which is a non-profit organization that was established to promote the use of gold and gold products internationally. In addition to marketing and supporting gold producers, the World Gold Council also researches gold mines and creates standards by which to evaluate gold mining prospects.
Another, less common definition of grading refers to the concealment of precious metals ore by workers who have mined it. This definition had greater applicability and was used more frequently during the late 19th century, when so-called high-graders would often hide gold ore in their lunch pails. To combat this problem, mining companies often required their employees to open their lunch pails, turn out their pockets, and shower following their shifts.
The World Gold Council on Grading
The World Gold Council defines a high-quality underground mine 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. The council recommends using cost per ounce, not gold ore grading, to evaluate a gold mine.
Using the World Gold Council's 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.