As a sibling comment said, gold was effectively money. Having more money, without having more products to buy, effectively triggered massive inflation. Prices went up, but the actual supply of goods and services didn't change much. The Spanish economy suffered massive inflation, as did Europe in general to a lessor extent.
It's interesting that mining gold and silver is similar to printing more money; we usually think of inflation as represented by debasing coinage but there's been a few circumstances where flooding the local economy with precious metals is the same effect.
Notably, the 'massive inflation' was a rate of 1-1.5% per year...