You might want to consider proposing a sub-tag for military=danger_area specifically for mines. Eventually maps can choose to add rendering like a mine icon in addition to the danger area markings.
I would suggest adopting hazard=minefield (in addition to the other tags you use) for use on paths/roads/routable objects going over or skirting the minefields as well. The hazard-tag is a proposal, but has been used in the field a good number of times (coincidentally, a few times in Serbia).
Edit: I'm now on some NSA list, aren't I? Hi guys! Just finished Snowden's book, it was great!