Ore grade

Ore grade is a measure that describes the concentration of a valuable natural material (such as metals or minerals) in its surrounding ore. Ore grade is used to assess the economic feasibility of a mining operation: the cost of extracting a natural material from its ore is directly related to its concentration, and the cost of extraction must be less than the market value of the material being mined for the operation to be economically feasible.

Ore grades for precious metals and gems are usually expressed as an amount of material per ton (or tonne) of ore. Ore grades for base metals and industrial minerals are usually expressed as a percentage. The ore grade required for economic feasibility varies widely based on the value of the material being mined. For example, the Argyle diamond mine in Australia produces diamonds out of ore graded at 7 carats (1.4 grams) per tonne, or about 1.4 parts per million, at a value of about 7 USD per carat or 35 USD per gram (the Argyle mine is considered to have high ore grade, but low value per carat, when compared to other diamond mines) [http://www.goldismoney.info/forums/showpost.php?p=6226&postcount=3] . Conversely, zinc mines may require an ore grade of 8% or more by total weight to be economically feasible [http://66.102.7.104/search?q=cache:e-ydt9-GD3MJ:minerals.usgs.gov/minerals/pubs/commodity/zinc/720496.pdf+%22Copper+mine%22+%22ore+grade%22+%22economically+feasible%22&hl=en] , as zinc currently trades at prices of about 1300 USD per ton [http://www.arcon.ie/s/ZincPrice.asp] . These data indicate a diamond value at the Argyle mine of about 50 USD per tonne of ore, and zinc value at a hypothetical 8% ore grade mine of about 90 USD per ton of ore, showing the similarity of economic reward for a similar amount of mining effort (although other extraction costs do factor in and may differ considerably).