Numismatist: In medieval Spain, most gold coins were minted from gold mined in West Africa, in the area that is now Senegal  The gold mined in this region was the purest known  Its gold content of 92 percent allowed coins to be minted without refining the gold, and indeed coins minted from this source of gold can be recognized because they have that gold content
The mints could refine gold and produced other kinds of coins that had much purer gold content, but the Senegalese gold was never refined
The only unrefined gold from which coins could be minted was Senegalese gold.