Mine will often have mine modifiers that change either the layout or the gameplay mechanic for that specific mine. They can be seen just before starting a mine in the middle section of the menu.
You can press on the modifier icon in the section for a detailed description.
COAL: The mine contain either no or only coal
IRON: The mine contain either no or only iron
GOLD: The mine contain either no or only gold
DIAMOND: The mine contain either no or only diamond
PICK HITS: Fixed amount of pick hits for this mine is indicated under this icon
DEPTH: The depth at which the idol for this mine is located
LOADOUT: Let the player know if he can use custom loadouts or if the event has a specific one
BOOSTER: Let the player know if he can use random cards or specific one
PICK REPAIR: Let the player know if he can repair the pick once it's broken
FIXED MINE: If a mine has the same layout every time, you will see this icon
HARDNESS: Represent the multiplier for the pick hits. (IE: Hardness 2: dirt block will cost 2 hits instead of 1, soft rock will cost 4, etc...)
MISSIONS: Let the player know if he has something specific to do in the mine
POSSIBLE REWARD ICONS
The middle section also contain what reward(s) you can possibly get from completing the mine. Sometimes, the reward(s) are different when you complete the mine multiple times.
Here are some of the most common icons:
Museums: Completing the mine will give you a random artifact, of a specific rarity from a collection of this world.
Cards: Completing the mine will give you a random card, of a specific rarity from all the cards available.
Shirts: Completing the mine will give you a random piece of gear, of a specific rarity from all gear available.