Así aparece en el Simon & Schuster en el contexto de minas

Hace poco trabajé en una traducción relacionada a minería y así se referían a "ley". Ver definición:

"Ore grade" is a measure that describes the concentration of a valuable natural material (such as (Any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.) metals or (Solid homogeneous inorganic substances occurring in nature having a definite chemical composition) minerals) in its surrounding (A metal-bearing mineral valuable enough to be mined) ore. Ore grade is used to assess the economic feasibility of a (The act of extracting ores or coal etc from the earth) 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 are usually expressed as an amount of material per (A United States unit of weight equivalent to 2000 pounds) ton (or (A unit of weight equivalent to 1000 kilograms) tonne) of ore. The ore grade required for economic feasibility varies widely based on the value of the material being mined. For example, the (Click link for more info and facts about Argyle diamond mine) Argyle diamond mine in (A nation occupying the whole of the Australian continent; aboriginal tribes are thought to have migrated from southeastern Asia 20,000 years ago; first Europeans were British convicts sent there as a penal colony) Australia produces diamonds out of ore graded at 7 (A unit of weight for precious stones = 200 mg) carats (1.4 (A metric unit of weight equal to one thousandth of a kilogram) grams) per tonne, or about 1.4 (Click link for more info and facts about parts per million) parts per million, at a value of about 7 (Click link for more info and facts about USD) 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) (*). Conversely, (A bluish-white lustrous metallic element; brittle at ordinary temperatures but malleable when heated; used in a wide variety of alloys and in galvanizing iron; it occurs as zinc sulphide in zinc blende) zinc mines may require an ore grade of 8% or more by total weight to be economically feasible (*), as zinc currently trades at prices of about 1100 USD per ton (*). 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).