Detonating Mines is Instant
8% increased Area of Effect 
Laying and detonating mines are two separate actions. Therefore, mine laying speed modifiers do not affect detonation time.
Detonating mines is considered a (non-damaging) spell, with base casting speed of 0.2 seconds. During this time, two quick detonation animations play simultaneously; that of the character casting, and that of the mine(s) exploding. Detonating multiple mines at once does not increase the cast time.
When a player takes Volatile Mines, the player's need to activate the detonation hotkey still exists. It is only the casting time that is removed.
- Mark_GGG (January 21, 2014). "Volatile Mines - Is Not Work". Path of Exile Forum. Retrieved March 11, 2014.