Correct, LB is above LT. Incidentally, holding LB and tapping up on the Dpad is the primary way to target closest hostile. So the same process with holding LB but tapping right or left instead is how you target any targetable object.
Mining can be very lucrative if you use the method of dumping the low value ores, and filling up on the valuable ones. It can become a little tedious after a while. You only get 3ish ores from each rock, so it’s a lot of scanning, and maneuvering to each rock.