I ran across a local story that said the material used to make the WWII bombs came from mines near Durango Colorado. But I thought at the time most uranium was coming from the Belgian Congo. Do we know the breakdown of where the Manhattan projected sourced its uranium from?
There were 3 main sources of Uranium for the Manhattan Project: the Belgian Congo, Canada, and Colorado. Over 2500 tonnes of Uranium for the project came from the Congo, while only about 700 tonnes came from Colorado and several hundred tonnes came from Canada. Natural Uranium (which contains only 0.7% of the fissile U-235 isotope naturally) was "enriched" via various processes to increase the content of U-235 until it could be used in bombs (specifically in Little Boy). It was also used to fuel fission reactors which bred Plutonium to be used in Fat Man style bombs (and in the "gadget" test device). Most of the nuclear materials in those bombs would have come from mines in the Congo but a sizable percentage would have come from Colorado and Canada.
The ore came from several sources: the Belgian Congo (about 72% of it), the Colorado Plateau (14%), the Eldorado Mine in Canada (9%), and some miscellaneous sources (5%), mainly ore captured from Germany by the Alsos group.
Here is a graph that shows the different amounts of uranium acquired from the different sources over time. Note that the quality of the ore varied dramatically; the Belgian Congo ore contained between 6 and 75% uranium oxide per mass of ore, the Canadian was around 25-30%, and the Colorado ore was more like 0.25%. The process for rendering the ores into uranium oxide was pretty complicated.
All of these graphs and even more data can be found in the once-secret Manhattan District History, specifically the volumes on "Feed Materials."