Too Many Catastrophes
Ok so by magical a cube of 470km appears out of nothing. For mercy I will consider it appears cold and at rest (no need of a gold huge meteor), in a flat desert land and avoid nasty things like all the air moved the volum of the cube moved (the shockwaves per si can make any nuke looks like a small bang).
Also let's say the cube keeps a cube by magic, otherwise you can think all that mass as a sort of high viscouseus liquid spreading very fast as a golden tsunami for over even a bigger area, maybe covering a continent and hitting the sea with nasty environmental consequences.
Note also some of the sea salt is made of gold but I'm unsure how it can affect sea wildlife. For sure the sea can become a slight less dense.
Not the last catastrophe can be the mass of the cube ripping trough the planet crust and reaching the mantle this is very speculative but one can expcet volcanos erupting and earthquakes all around and not even start to think about all that gold sinking to the core.
Let's also make the magic protect the planet rotation, you know what can happen if you concentrate mass in a ball? Well put a small lead pin in a baseball ball side and throw it, thats what they call an odd ball.
If there are sattelites over this planet their orbits can be affect by a huge Mascon (sorry ISS).
Economics
Rulling out all the world destruction thing we still will see bad things happening because gold is valuable because it's rare. Unless some major global power throw all his military at protecting the cube, maybe triggering a world war, gold now is a very ordinary thing. You can have balast make of gold to use in fishery, use it to make water pipes and so on as it now can be as cheap as lead (just a bit less unhealthy).
How gold will trigger an economic crisis depends on your world setup. 921
In a medieval setup kingdoms will slowly change all his currency to silver. Powerfull kings will be less powerfull. In a a more renaissense world the new formed banks sinks, the merchants are almost bankrupt and say goodbay to arts patronage. In a modern earth like society we are screwed, badly. Gold is an important commodite.
The bottom line is: The poor fool wished all the gold of the world is now more poor ans screwed than before. 752