Is there anyway to always capture an enemy mine?
I'm afraid not. The AI (As stated before) is quick to the trigger, and will demolish their mines in gloriously pixelated blasts.
Well, almost not.
For some reason, gold-mines do not blow up when captured. It's the only mine the 'AI leaves alone'. I have no idea if this is just happening in my game...But you should try it. Free gold AND settlers from another nation!
But be carefull with those mines...Their blast costs troops.
I'm pretty sure they blow up their own gold mines. You might just be getting lucky.
They'll self-destruct anything you can capture. Buildings(except mines) will take about 50%-66%(unsure of exact amount) and catch fire, causing further damage until it explodes or is fully repaired. Captured town halls will automatically train up a peasant, BUT you need TWO peasants to out-repair the damage caused by the burning. Exploding buildings will usually kill a guy or two, and mines can be especially lethal since there's no time to run. Best just point your howitzers at them(unless gold mines don't explode after all, then capture them).
They'll also kill off their own artillery, although this just kills the artillery unit.
It's fairly rare to take buildings without self-destructing, but it's somewhat common for artillery. It's really annoying if they somehow catch some of YOUR guns, and then kill most of them when you try to retake them.