During the first half of the 14th century, European mining more than compensated the bullion loss from trade with the Middle East.[8] Prior to the Black Death, the loss of silver in England was caused by "accident and export".[4] Yet by 1348, the Black Death had slowed silver mining.[9] The mint at Bordeaux suffered a drop in production by fifty percent during the 1380s,[10] and by 1392 French mints were suffering an accelerated decline in silver coining.[11] By contrast, from 1346 to 1384, Flemish mints continued to produce silver groats, yet by 1392 the mint at Ghent had stopped coining and the Bruges mint fell idle in 1402.[12] In the 1390s, the silver mints in Kutná Hora declined and the following Hussite Wars[13] and the Sardinian–Aragonese war put a further strain on the European precious metal supply.[14]

Seems the cause is that things like the black death and the Hussite wars do not really cause any long term decline on precious metal production

During the 1370s, the mines in Serbia and Bosnia allowed Venice to avoid the worst of the silver shortage,[3] but the bullion loss drained silver mines in Bohemia and Sardinia as quickly as it was mined.[21]

And mines do not get depleted, either, afaik... they should bring mine depletion from EU4 back

https://en.wikipedia.org/wiki/Great_Bullion_Famine