Uranium can be found in low concentrations throughout the earth's crust and also dissolved in oceans, although it is found at higher concentrations in a number of places. The largest mines for uranium are in Canada, Australia, Niger, Kazakhstan, Russia and Namibia as of 2015.
Uranium is about as abundant as tin and is more abundant than mercury, silver or gold. The ores it is mined from typically have it in very low concentrations of around 0.1 percent. Some mines in Canada, however, have ores which are as high as 20 percent uranium. Such high levels are very dangerous to mine because of the radioactivity of uranium; special measures must be taken to protect both the miners and the environment. Ores with more typical concentrations do not pose such a threat.
Uranium mining is somewhat easier than many other types of mining because radiation sensors can detect uranium ores. Shallow underground deposits are generally accessed through open pit mining, in which the surface rock is removed to expose the ores. Deeper underground deposits require underground mining in which the overlying rock is not removed. In situ leach mining is used with ores that are underwater on porous surfaces, where the uranium is dissolved and collected as part of liquid compounds.