This is inspired by a now-closed thread, "Plate tectonics, mountain building, and the Flood", over in "Geology and the Great Flood".
I wonder how young-earth creationists deal with that question -- do they suppose that all the various objects were created with all their mixtures of elements? Or is element-mixing yet another side effect of the Fall and/or the Flood?
Old-earth creationists like Hugh Ross, however, have much less trouble; Hugh Ross seems to accept mainstream astrophysics.
The chemical elements have several sources, each of which has a characteristic "production signature" -- a signature that can be calculated from nuclear-physics data and the characteristics of the various nucleosynthesis environments. The nuclear-physics data, in turn, could be calculated from Quantum Chromodynamics and the light-quark masses, but that has been too computationally difficult.
Here they are:
* The Big Bang. This accounts for hydrogen and helium -- but not much else. The BB was too dilute to produce anything much heavier than helium.
* Cosmic-ray spallation. This accounts for some light elements -- but is too weak to account for most of the element abundances.
* The interiors of massive stars. This accounts for s-process nuclei; these absorb neutrons, then beta-decay if they can.
* Supernovae, inspiraling neutron stars, etc. These account for r-process nuclei, which are produced by neutrons that are absorbed faster than the nuclei can beta-decay. And also for p-process nuclei, which are produced in strongly-heated proton-rich environments with lots of existing massive nuclei.
The Big Bang produced the Universe, while massive stars often eject much of their material into the interstellar medium, synthesized elements and all. Thus, the interstellar medium becomes enriched in heavy elements as time goes on -- which can be seen by correlating heavy-element abundances with ages of stars.
So the origins of the elements are no mystery -- it's remarkable how much progress has been made in this field.