Really unique idea!
The idea of revealing the tower as you gather mines is really creative. There were some things I would have liked though. I wish it were communicated better in game. Pausing the game and showing a picture of a left mouse click and then once the player presses it the tile is placed would have made this much better!
Difficulty and Telegraphing
I think the difficulty is perfectly fine for this game. However, what makes it difficult is the fact that there isn't much telegraphing where the triangle enemies are coming from. If you had a circle with an arrow showing where a triangle is going to be coming from this game would be much fairer.
If you decide to continue development this would be a really addicting game!