Mining companies may sell copper in concentrate or cathode form. As mentioned above, copper concentrate is most often refined using equipment at a different location than company mine sites. Concentrate producers sell a concentrate powder containing 24 to 40 percent copper to copper smelters and refiners. Selling terms are unique to each smelting company or copper refinery, but in general, the smelter pays the miner approximately 96 percent of the value of the contained copper content in the concentrate, minus treatment charges (TCs) and refining charges (RCs). TCs are charged per tonne of concentrate treated, while RCs are charged per pound of metal refined. These charges fluctuate with the market, but are often fixed on an annual basis. TCs and RCs tend to rise when there is a high availability of copper ore. Miners indicate copper concentrations, although they may be spot checked by a third party when en route to the refiner. Additionally, penalties may be assessed against copper concentrate according to the level of deleterious elements contained, such as lead or tungsten. Most smelting companies have strict limitations on permissible concentrations of impurities, and if concentrate producers do not meet these needs, they will be subject to financial penalties. Miners may also receive credits for “valuable” minerals, such as precious metals gold and silver. TCs and RCs are levied separately on these metals. Smelters generally operate by charging tolls, but they may also sell refined copper metal on behalf of miners. All of the risk (and reward) of fluctuating copper prices, then, falls on miners’ shoulders. Typically, copper concentrate is traded either via spot contracts or under long-term contracts as an intermediate product. For spot contracts, miners are paid according to the copper price at the time that the smelter/copper refinery makes the sale, not at the copper price on the date of delivery of the concentrate. For longer-term contracts, pricing is based on an agreed-upon copper price for a future date, typically 90 days from time of delivery to the smelter.