Mines, unlike asteroids, can pursue you, though they are much slower than your craft's top speed. Think of them as slow homing missiles. Thus, if you fly too slowly, they will catch up to you. Don't try to afterburn though--you'll plow straight into one at those speeds. Keep your speed in the 200-400 kps range, which is fast enough to outrun their pursuit, but slow enough to dodge any ahead of you.