Erbium (Er) [Z = 68]
The variations are substantial within the REE class of ore deposits, and the formation of an REE ore deposit gives little information about its classification. Besides, classifying REE ore deposits on the basis of only their genetic evolution would quickly induce misinterpretations. For instance, the class of copper-gold-uranium-REE-iron (IOCG) includes the well-known Olympic Dam deposit (South Australia), the iron deposits of Kiruna (Sweden), the iron-REE deposits of Box Bixby and Pea Ridge (Missouri, United States) and possibly the REE-rich Bayan Obo (Mongolia), the Palabora carbonatite-hosted copper, and the Vergenoug iron-fluorine deposit (South Africa). When examined in detail, these deposits are remarkably different.