There are no rules for using mines in the books (as far as I am aware), and it just leaves it up to the GM.
To trigger the mine, in some situations, Threat could be used. In others, proximity. And in some, a (failed) Vigilance check. However, there is no set method, and the obvious are often lackluster in certain contexts.
Secondly, there is the question of setting mines. What is usually called for is a Mechanics check, determining both the mine’s damage and whether or not it triggers crits or other qualities such as Blast.
This is very sketchy to use, especially on a large scale such as with a minefield, and is not especially reflective of reality. Damage and severity is not caused by how well-placed the mine is so much as it is by the victim’s proximity to the mine among other variables.
So, I have a few suggestions for how to handle the two main circumstances in which you’d encounter mines:
First: Single mines, or at least a (very) small number of mines in predetermined locations, where it would be plausible to set each individually.
For this, I would suggest a Mechanics check to place the mine, which in this case determines not the damage etc., but rather the difficulty to notice/avoid it. There’d be a base difficulty (say, Average), modified by the results of the check. Success increases the difficulty once, and each subsequent two success increase the difficulty again (to a maximum of Formidable). Each 2 Advantage upgrades the difficulty once. Setback is determined by the GM, based on the surroundings (is it hidden on a wall, just around the corner, but in plain view? No Setback. Is it concealed in a pile of mechanical junk? 2 Setback).
Failure and Threat or Despair on the victim’s Vigilance check are spent like Success and Advantage or Triumph, increasing damage and activating qualities. This allows both the minelayer’s skill and the victim’s awareness to affect the final outcome, which I think works well.
Here, I have two suggestions. One based on a conventional roll, the other based on “luck.”
Conventional: To lay the minefield, the acting character(s) must make a Mechanics check (Survival, Leadership, and Knowledge [Warfare] are acceptable alternatives) of an appropriate difficulty to lay the mines well. Threat can be used to leave some avenues uncovered, failure decreases the minefield’s efficacy by increasing its difficulty once. Triumph could be used to upgrade its attack roll, and 3 Advantage to add a Boost.
Then, anytime someone takes a movement maneuver inside the minefield, it (the minefield) “attacks” the character and rolls YYG against a base of Easy (at GM discretion, it ignores the target’s Defense).
If it fails, no mine detonates. If it succeeds, resolve like a standard combat check.
“Luck” based: This is the simplest and easiest, and my preferred method. The minefield is lain automatically with no check (or it could be rolled, but it would affect things outside the minefield’s efficacy). Whenever a character makes a Move maneuver within the minefield, he must roll a Force die. If it generates a LS pip, he’s fine. If it generates a DS pip, he detonates a mine and takes base damage. If it generates double-dark, he detonates a mine and takes base damage and either activates Blast or suffers a crit, at GM discretion.
Drawbacks to luck-based: A given character has a greater than 50% chance of triggering a mine. One way to adjust this would be to flip who’s getting “lucky” and have the mines trigger on light pips, and gives a greater chance that Blast/crit is triggered.