All gems are pristine gems in the making. You get a lot of xp from fusing gems. 60 flawed and/or 20 normal gems are fused into one pristine. So just mine everything and fuse.
From my experience farming void ore, the orichalcum nodes give a ton of tier4 gems constantly. Also as someone above mentioned, elite chests, but those are just 1 run per day. So slap your mining luck gear and go smack some cum ore. I have about 300lbs worth of gems from farming 4-5 days of ore.
Getting the actual essences to cut/fuse those gems will be hard, so just focus on life and earth purple essences, the ones you can actually farm from mobs. You can also get soul from the deer poop, but those are hard to get in larger quantities quickly.
Since i play on a dead server i have thousands of motes stashed up.
I will look into the orichalcum ore and try to farm that, but im guessing those nodes will be very contested