Mines were released in a much smaller quantity and are quite powerful.
Official OpenSea Collection:
Dwarfs discovered mountains full of $BERYL, it's time to dig mines, but don't forget brave dwarfs that trolls are around, and they want their share! There are only 500 mines, dig your own!
Each mine allows you to stake 5 dwarfs and get a buff that increases the overall $BERYL production levels. Each dwarf mines 125 $BERYL per day in this mine, unlike the standard levels, where the mining is 50 $BERYL per day.
Starting on 02/10/2022 Mines will need to be staked on a piece of land for the bonus to apply!
The higher the level of the mine, the more dwarfs can work in that mine. (This mechanics of leveling will be implemented in the first week of February.)