Britannica Sources used in this answer

Why are some gold ores called refractory?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A diagram showing the periodic table entry for gold, with the symbol Au, atomic number 79, atomic weight 196.96657, electron configuration, and labels for its properties as a solid transition metal with a face-centered cubic crystal structure. — gold The precious metal gold is a chemical element with the symbol Au. Its square on the periodic table details some of its properties, including its atomic weight, atomic number, and crystal structure.

Gold ores are classified as refractory when they are not easily processed through standard cyanidation. This difficulty arises because certain substances within the ore interfere with the extraction process in three primary ways:

Reagent consumption: Some materials consume the cyanide reagent before it can effectively dissolve the gold.1
Preg-robbing: Certain substances preferentially adsorb the gold as it dissolves, preventing its recovery.1
Physical encapsulation: The gold particles may be completely surrounded by other minerals, preventing the cyanide leach solution from reaching them.1

Refractory ores frequently contain sulfide minerals such as pyrite, pyrrhotite, or arsenopyrite. To extract gold from these materials, the interfering substances must first be destroyed through oxidizing processes. Common techniques include roasting the minerals at high temperatures or using high-pressure autoclaves to treat the ore with oxygen-bearing gases. Once these barriers are removed, the gold can be successfully recovered using standard cyanidation.1