The Shinkolobwe Mine was the best Uranium mine during WW2. It had great concentration of uranium oxides on the order of 20% to 65%. By contrast, all other Uranium mines I've read about had concentrations no greater than 1%. It's located in the Belgian Congo, today the Democratic Republic of the Congo.
This makes it a very strategic site for the Manhattan Project.
However, the wikipedia article mentions this:
The mine was closed in 1939 and flooded. The US Army sent a squad from its Corps of Engineers to reopen the mine, expand the aerodromes in Léopoldville (now Kinshasa) and Elizabethville (now Lubumbashi), and extend the port at Matadi, on the Congo River. Between 1942 and 1944, about 30,000 tons of uranium ore were sold to the US Army.
(It's worth nothing that there's no citation for any of that.)
This brings up a few questions.
Exactly when was the mine flooded?
Why was it flooded? No other Uranium mine compared to this. Was it German "Scortched Earth" practice? (Belgian Congo was owned by Belgium, although Belgium had not yet been invaded as of 1939.)
Exactly when did the US Army Corp of Engineers arrive?
Exactly when did the mine begin producing again?
Googling around only brought me results on current affairs. Apparently the mine is shut down today but the UN monitors it as a security risk with lots of rumors.