What Tarner can tell about these gates at about 20 yards away is that they display the typical strengths and weaknesses of drow war-construction. Which is to say that they are very strong against magical assault but not nearly so good against a strong, physical pounding. Iron is a magically inert compound, so blasting them almost certainly won't work. However, even iron gates are only so strong as their cross-bar. Moreover, black iron is HEAVY. So the the crossbar here is probably wooden. Maybe heavy wood, but still. You should be able to pound it with a few good strokes... if you can get close enough.