The mines in question are on Cyseal beach. From maximum zoom-out they are initially visible; when you zoom-in they become invisible; when you zoom-out again they remain invisible.
I reported this to Larian and they acknowledged that it was a bug due to be fixed in a patch.
I thought that the fix might have been a part of this major patch but it would appear not.
My party has a max perception of 6 and are now at level 5. Given that this is an early part of the map/game I would have thought that the mines should be visible at this stage.
