... wait. I made an alumite pick and gave it silk touch specifically for this, and now I'm being told I have to upgrade past that? I'm annoyed. I thought level 6 was alumite, not manyllyn.
Don't quote me on that
BUT, I started with an steel pick, then remembered you need alumite for Cobalt.
Just copied my save into the 2.1.6 download I've been ignoring, and tested for you, myself, any anyone else who cares.
Alumite pickaxe head, nether ore mining results:
Yes:
Netherrack
Ardite
Lapis
Lead
Gold
Coal
Ferrous
Redstone
Tin
Quartz (dropped quartz crystals)
No:
Salt
Rutile
Cobalt
Sulfur
Vanilla quartz dropped the items, everything else dropped the ore block. Silk touch is still useful, as you'll get more and consistent output by pulverizing the quartz, rather than the varying drops from a pick.
Further tests on the above "No" ores:
Thaumium: no
Obsidian: no (YES Ardite)
Cobalt: yes
Bound Pickaxe: yes
Pickaxe of the Core: yes
Manyullyn: yes
Ardite: ONLY mines cobalt ore
Flux-Infused: no salt/rutile/sulfur (YES cobalt, ardite)
So, seems we need to make an obsidian OR alumite pickaxe head, then use that to mine Ardite to make an Ardite head. Use that to mine Cobalt,
then make a Manyullyn pickaxe head.
THEN we can mine sulfur ore for reactors and pyrotheum blend, plus I guess titanium ore and nether salt. Isn't salt free though?
Edit: forgot the Flux-Infused pick!