Copper concentrate: whatit is and how it isvalued.

Copper ore usually contains only a small percentage of copper. To make it worth transporting, the ore is crushed, ground and passed through flotation at the mine, producing a concentrate in which the copper minerals are much richer. That concentrate is the main raw material of copper smelters.

A smelter does not pay for every unit of copper in the concentrate. Terms generally pay for most of the contained copper and deduct a treatment charge per tonne of concentrate and a refining charge per unit of payable copper. Gold and silver in the concentrate can also be paid if they exceed agreed thresholds.

Impurities matter as much as grade. Arsenic, bismuth, antimony, mercury and other elements can cause penalties or make a concentrate unsuitable for a given plant, because each smelter has its own limits for what its process and emissions permits can accept. Some concentrates are blended to bring impurities within those limits.

Because value depends on the exact composition, sampling and assay are central. Samples are taken during loading or discharge under an agreed procedure, buyer and seller each analyse them, and an umpire laboratory settles any difference beyond an agreed margin. Moisture is measured separately, since freight and payment are calculated on dry weight.

For an intermediary, the work is to match each concentrate's profile with a smelter whose limits it fits, and to make sure both sides work from the same independent results.