Subject: How did natural uranium form on Earth?

If supernova produce uranium, how did individual particles clump together to 
form enough uranium to dig up as ore on Earth? It seems that it would all be so 
thoroughly mixed together with all the other particles forming a planet that no 
two uranium atoms could get near one another. How would you end up with clumps 
of the stuff? The same could be said of other heavy elements. What am I missing?

Re: How did natural uranium form on Earth?