A few more points you could add is what got him interested in explosions in the first place, the first fireworks show he saw, a story from his older brother? Also as BlindJester suggested, you should really explain in detail how you got your cutie mark, for example what was this mishap you are talking about. Also lets not forget your pony is only a colt, so still a young pony, you probably will not have an active mining colony till your a grown stallion. So maybe starting as a stallion would be a better idea then a young colt, as you might have to Rp for a while before you can get your mine going if your a colt. But onto some of the good points, you have a strong idea for a character application, and the loves to blow stuff up can have huge potential in a fun Rp storyline. Not to mention the die hard personality you have gave your pony. So you have a great and solid start, and a excellent idea for a character. One more suggestion I could offer, and a point BlindJester stated was your character's name, would be a great nick name but maybe something more driven by your personality for a name would be a better choice.