The Custom TNT Igniter allows you to set parameters for setting off TNT in Minecraft. You can set it to only destroy a set type of block or to ignore that particular block(s) when it explodes. Now you have the ability to clear areas underground without worrying much about destroying precious ores.
But even better is the ability to enchant the igniter with Silk Touch. This will give you a much broader range of obtaining blocks without breaking them individually like with a silk touch enchanted pickaxe.