Very good start
Initially, I just thought this was yet another samey-TD game, but I decided to give it a chance.
I really like the mines - having to balance between defensive structures and resource collection can be tricky in the later levels.
Overall it definitely kept me entertained, until Firefox crashed :(
However, just a few possible suggestions -
-Upgradable weapons (Increase damage, range, etc)
-Place several weapons (currently if you want to place a few you have to keep clicking on the weapon button, maybe make the placement method more like Desktop tower defense)
-Add a few more map types (different routes for the enemies), different terrain, etc
-More enemy types
-Different weapons having higher/lower effects on different enemies (e.g. Flying enemies can only be hit by certain weapons)
-More sounds (different sounds for different weapons)
-Different projectiles for different weapons
Best of luck,