There is that much gold in the world.

When the Spanish conquered the Aztecs and the Inca, they spent over 100 years bringing back all the gold. Tens of thousands of ships, laden with gold. The Inca alone were estimated to possess 15,000 cubic meters of gold, with the majority of it covering government buildings, temples, and some of the main roads. The Aztecs had so much gold they stored EXCESS in enormous underground pits that the Spanish tried to loot but realized that they weren't going to be able to get all of it because by the time they started Mexico was beginning to clamor for independence and they had to focus on maintaining stability (which is hard when you are devoting 80% of your navy in the area to looting).

The Mali and Ghana Empires may have had even more gold. Mansa Musa, nearly a legendary figure, was said to be so wealthy he would give bags of gold to every single person he met traveling from Timbuktu to Cairo and back. Via North Africa (Tripoli, Tunis, Algiers, Oran, Marrakech, etc)!

Some medieval authors who showed more knowledge of Sub-Saharan Africa than the norm, indicated that Ghana was a land covered in Gold, and that the Niger River (then called by a different name), had so much gold in it that it shone in the day time like a thousand Suns (that is most likely a historical embellishment, since they also liked to preface such descriptions with "don't go there, you will burn to ashes."