ReviewGold in iron oxide copper-gold deposits

- Iron oxide copper-gold (IOCG) deposits contain economic or anomalous gold.
- The gold is present as native gold, electrum, and gold-bismuth-antimony-tellurium alloy.
- The gold distribution is controlled by gold contents in host rocks and the efficiency of precipitation mechanism.

Iron oxide copper-gold (IOCG) deposits contain economic or anomalous gold, and the gold distribution is important both for its economic significance and ore genesis. However, the gold distribution in IOCG deposits and its controlling factors remain unclear. The gold grades and tonnages of selected thirty-six deposits in some well-defined IOCG provinces are compiled in this paper. The gold grades in these IOCG deposits range from 0.01 to 1.41 g/t (averaging 0.41 g/t), and ~ 90% of them are less than 1 g/t. The gold tonnages range from 0.6 to 483 t (averaging 64 t), but with the exception of the giant Olympic Dam containing gold of 2968 t. The Cu/Au ratios of IOCG deposits are significantly variable, ranging from 0.7 to 64, but most values fall between 1.0 and 6.0. The gold is present in three forms: 1) native gold, 2) electrum, and 3) gold-bismuth-antimony-tellurium alloy. The gold distribution is controlled by gold contents in host rocks and the efficiency of precipitation mechanism (e.g., cooling, fluid-rock interaction and fluid mixing). In order to find gold-rich IOCG deposits, at province scale the most important thing is to focus on areas both with gold-enriched host rocks and efficient depositional mechanism and at a deposit scale the exploration of gold-rich deposits should also focus on low-temperature deposits.