Origin of heavy elements

[farmerben]

Standard cosmology has the early universe with very few atoms of elements heavier than lithium.   Multiple generations of stars and supernovae account for roughly the proportions of oxygen, iron, and other mid-level elements we see.  But the heavy elements are barely produced in stars except at the exact moment of a supernova.  

Another way heavy elements can form is when two neutron stars collide.  These can eject plumes of degenerate matter that are similar to planet sized atomic nuclei of protons and neutrons.  These fission down in seconds leaving elements like uranium and even heavier ones that do not survive long enough to contribute to other star systems.  

The early universe had quasars and black holes with insanely large accretion properties.  Could the heavy elements have formed in the early universe?  What evidence could we look for regarding the origin of heavy elements?

[kerbiloid]

As the uranium half-life is 4.6 Gy, the uranium ore would be ore of lead.

[magnemoe]

15 hours ago, kerbiloid said:

As the uranium half-life is 4.6 Gy, the uranium ore would be ore of lead.

Who is true, but 30%  would still be present even if as old as the universe, granted it would not be much U 235 left. 
We know it was more back then earth was young mostly because the natural nuclear reactor 1.7 billion years ago then  U 235 concentration was 3.1% while its .72 % now. 
But not sure if we know how the creation process of heavy elements work in details, might more U 235 be made than 248 or less ? 
Same with stable heavy elements. 
 

[farmerben]

Another question:

Our periodic table of elements gives the atomic mass based on the average of various isotopes found on Earth.  I've never heard of problems arising due to having different mass due to different isotopes.  

But, in another star system, or even in the outer parts of our solar system.  Could the ratio of isotopes be different?  Meaning we can't rely on default atomic masses like we have found on Earth.

[kerbiloid]

1 hour ago, farmerben said:

But, in another star system, or even in the outer parts of our solar system.  Could the ratio of isotopes be different? 

Deuterium concentration is significantly different. So be many others, depending on their origin.