After excavating in a few threat level 1-6 worlds, I've found a single piece of gold ore. I have no way of knowing just how far down I've been digging but It feels like quite a ways down, in fact most of my deaths underground are falling down long unlit tunnels.
So far all of my gold+ ores have been found in random dungeon(?) chests. Though dungeons are quite hard to come by and if I die in one it takes way too long to run back to them.
Do I just need to keep digging? Does the threat level have anything to do with ore quality? Can higher tier ores be found on every planet if you dig deep enough?