To get the skill Mining Bomb, you need to reach L 30 in Mining
Press L to access your Trade skills and drag Mine Bomb to your shortcut meny
Now use the bomb more then 100 times without being near any rock that are used for mining.
This will take some time, considering it has 2 minute cooldown.
You can check your progress by using ALT+O and go to Trade skill - Mining
I actually got this when I used 5 bombs and recived the in game achivement