Metallic minerals are very important to most Saharan countries. Algeria and Mauritania have several major deposits of iron ore. There are also uranium mines, mostly in Niger. A lot of phosphates are in Morocco and Western Sahara. Petroleum is mainly found in Algeria, where it is very important to the economy. While mineral exploitation has led to economic growth in Sahara, this has rarely helped the indigenous population, as skilled workers have been brought from other countries.