New World gold was a short term benefit to Spain, but a long term problem. Obviously, having all this extra cash allowed Spain to buy a lot more than it otherwise could - more guns, more ships, etc.
But it created problems in the long term. Gold in and of itself is not wealth. True wealth is increased productive capacity. A gold supply in excess to the need to monetize that increased productivity simply leads to inflation which destroys economies. Also, being able to fund Spain's wars with New World gold meant the crown did not need to go to the Cortes (parliament). This meant Spain would never the institutions of strong government that the English and Dutch did (the same problem affected France whose sovereign had various direct taxes - like the hated gabelle - that enabled the king to do whatever he wanted). Therefore, Spain is likelier to develop a more effective government based on some kind of consent.
The big issue is that without that New World gold, what pays for all the wars against the Ottomans? The Ottomans were very powerful at that time, and the New World gold helped level the playing field.
The big problem with Spain controlling any African gold is that the climate is still petilential to Europeans. If Spain tries to control the western sudan, they will have immense mortality. I don't see Spain suceeding. Furthermore, involvement in Africa will bring them in conflict with the Portuguese.
Spain may concentrate on north Africa, and possibly conquer and keep control of a large part of the coastline. But the Ottomans are still going to be quite a threat for the next century or so.
For the ottoman's the solution is Austria, Poland, Russia, and Persia