Treasure Mine is a game mode that will allow you to get chests with interesting prizes, through different game proposals.
Once you enter the Mine, you will be able to get close or far from the chests by winning picks. To win those, you will need to play the game that is available at that moment. If you win, you will get picks, but if you lose, they will be taken away from you.
The more picks you get, the more chests you will be able to unlock. On the upper part of the screen, you will be able to see the picks you currently have, as well as the chests that still need to be unlocked and the amount of time you have to do so.