Gold became the standard coin of trade first primarily for its metallurgic qualities, but it remained so because of its supra-natural qualities. Gold, you see, must constantly remain in circulation; the movement is essential to counteract the malign will of the gold itself.
Gold, you see, is a heavy, lazy thing; it pulls itself towards the ground, and desires above all else to nap lazily in a cool, dark place, perhaps with a stray sunbeam warming its back, in a large pile of its kin. The subtle whispers it trickles in the ears of mortals, the sapping light it exudes, the way it pushes its weight all the way down to the boot heels of those who carry it, causing them to drag their feet, all compel those who carry gold disturbed from its slumber beneath the earth to return it to such a state, till eventually they lay all gathered somewhere in an enormous pile.
Two curious things happen when a concentration of gold is formed in this way. One, fearing that its slumber be disturbed again, it sends subtle vibrations through the air which induce a kind of monomania, causing heady fools to rush to discover and uncover it. Many will be drawn by this call, though inevitably violence will erupt and only the most brutal and deranged will lay claim to the prize. This is the first part of the selection process.