Research suggests that by Carolingian times gold was being imported from Byzantium and some from Muslim Spain, although silver had been mined more locally. This is likely a factor in Carolingian shift from minting gold solidi to silver denarii, combined with growing economic need for smaller types of currency. It also appears copper work took off during Carolingian times and copper is far more available in open pit mines. Iron ore would have been sourced in German deposits.

By the high middle ages there was more iron ore and silver metal mining than the Romans in Europe. The waves of 'Christianization' of Germanic lands east of the Rhine and north of the Danube, and the subsequent economic development and industry that accompanied formalization of medieval rulership in those territories led to mining of tremendous deposits of precious and base metals in the Alpine regions and thence further east.

High and late medieval technologies developed which allowed better exploitation of resources, including mining technologies (that allowed one to go deeper), metal separation technologies (allowing more extraction from waste). Archaeology has proven the increased number and diversity of smelting locations during this period, with many of them nowhere near mines, suggesting that the costs of moving metal to smelters in the woods was more efficient than bringing the wood to the mines (wood being the fuel for fire). By the late medieval period coal was firing large blast furnaces turning out greater volumes of metal through greater extraction.

This all being said, these are metal ores which exist below ground. Technological limitations prevented deeps mines and so they would be abandoned once they started filling with water or noxious gases. For this reason I doubt that any mines from the Roman era were in use even by the early medieval period, even if they could have been found after centuries of growing over.

Mining for stone (marble, shale) was surface mining and so the pits still persisted from Roman period - even today we extract stone from those same pits. Of course new ones were found as well.

Yesterday I hiked to an abandoned medieval blue marble pit 700 meters up in the Ariege (French Pyrenees) - the remains of late medieval technology still visible was impressive. Blocks of marble 1.5 x 2 x 3 meters were extracted and brought down the mountain whole.