Spain got there silver from the Philippines and Potosi, Peru, and from trading with china and other countries and merchants. The atlantic ocean was used constantly when the Philippines trades with spain, 5/7ths of all the silver available in the atlantic ocean was traded with each other and this helped cause global trade.¬ Silver was the cause of the age of exploration in Europe and china. Silver was very valuable to china; it was the only form of payment they allowed for a while. Spain mined for silver in the Americas to trade with china.
Spain wanted to go to Mexico to find a direct passage that connects the Americas to china in 1571. They would have direct access to Chinese markets