Whimsical idea: create your own gold mine

This is an idea that is similar to the old alchemist's dream of turning lead to gold. What you could do instead is to turn mercury into gold. How? You need a source of neutrons and a some Hg 196, an isotope of mercury, which is in sparse concentration in nature.

the isotope needed would only be in concentrations of less than 1 percent

It appears that mercury will accept a neutron, since it has a pretty good size barn .  There's two problems (that I know of).  1) getting a source of neutrons and 2) getting the isotope needed, since it is rather sparse.  Assuming you could do that, you could make gold by bombarding the mercury with neutrons.  It will beta decay (electron capture) into gold, which assumes that you get a stable isotope.

How do you get neutrons?  Usually this is done with radioactive sources ( as far as I know).  There may be a couple other ways.  The first way is by making a Polywell device and fusing deuterium.  This will produce your neutrons all right, but you may want to slow them down.  Also, you don't know if this is going to produce the number you need in order to make it worthwhile.

Another way is by way of LENR.  Widom Larsen proposes that a suitable hydride can make ultra low momentum neutrons.  These neutrons, assuming that they exist, can be used to bombard the mercury and make gold.

mercury to gold?  you gotta be kiddin' me

This is a bit whimsical because- once you make the gold, and assuming that you can make a lot of it at a relatively cheap price ( quite a presumption by the way), you will have destroyed its economic basis.  Sort of self defeating.  But diamonds can be made artificially.  If there was no way to tell them from the real ones, diamonds would be worthless. ( ha ha)