How Much Gold is in Chalcopyrite?

Chalcopyrite is a common copper-iron sulfide mineral that is found in copper ores around the world. It has a brassy yellow color and a hardness of 3.5-4 on the Mohs scale. Chalcopyrite is the most important source of copper, and is often found along with gold and other minerals. But how much gold can actually be extracted from chalcopyrite deposits?

The gold content in chalcopyrite is generally quite low. Most chalcopyrite deposits contain well below one gram of gold per metric ton of ore. Even ore bodies with good gold grades rarely exceed 5 g/t. This is far lower than the gold content of ores that are primarily mined for their gold rather than their copper content.

For comparison, many gold deposits that are considered high-grade contain over 5 g/t of gold. Some exceptional deposits have grades over 50 g/t. At those concentrations, visible gold can often be seen in the rocks. But in chalcopyrite, the tiny amount of gold is spread diffusely through the crystals and cannot be seen.

There are a few reasons the gold content of chalcopyrite is so low:

  • Chalcopyrite formed deep underground under high temperatures and pressures. Gold tends to get concentrated in mineral deposits that formed closer to the surface.
  • Gold does not readily substitute for iron or copper in the chalcopyrite crystal structure due to differences in atomic size and charge. This limits the amount of gold that can be incorporated.
  • Other sulfide minerals like pyrite and arsenopyrite have crystal structures more amenable to hosting disseminated gold. Gold tends to prefer those minerals over chalcopyrite when both are present.

While the concentration of gold is low, the huge size and tonnage of some chalcopyrite deposits means they can still contain economically significant quantities of gold. The gold is recovered as a byproduct during the processing of chalcopyrite ore for its copper content.

Advanced smelting and leaching techniques allow even tiny amounts of gold to be extracted. This contributes extra revenue for mining companies, helping offset the costs of copper production. However, chalcopyrite should not be considered a major ore of gold except in unusual cases where gold values are known to be exceptionally high. For the vast majority of chalcopyrite deposits, their gold content is of secondary interest compared to their much higher copper grades.