Why does the uranium content of many ores make up less than 0.1 percent of the rock?

The uranium content of many ores is low—often less than 0.1 percent—because uranium is widely distributed throughout the Earth's crust, occurring at an average concentration of only about two parts per million.12

Because uranium is so dispersed, it rarely forms high-grade deposits. Instead, it is found as a minor constituent in more than 200 different minerals. Even in areas where uranium is considered an economic resource, it exists primarily as a small amount of uranium-bearing minerals embedded within larger rock formations, such as sandstone or conglomerate.23

This low concentration is a significant factor in uranium processing. Because the uranium is present in such small quantities and is not amenable to traditional smelting, physical concentration methods like flotation or gravity separation are generally ineffective. Consequently, the entire volume of ore must typically undergo hydrometallurgical procedures, such as acid or alkaline leaching, to extract and purify the uranium.34