Well I’m gonna be frank. You do not need the pickaxe early game. There are no nodes on the main island to use it on to gain ore. In fact as of launch (could be changed later) there are only two materials you can mine. First is keltonite ore and the second is quest related ore item called rainbow ore
Its located in the tools tab and so far I have not found a use for it other then selling it. It actually is very plentiful.
Location: Black Barrow, it is is everywhere. Be sure to bring a pickaxe
Use: Unknown, selling?
This i what it looks like:
This quest related. slight spoilers but nothing major Rainbow ore, which is only used briefly when going to the Brisk observatory on Astral Heights
Location: Cave south of Astral Heights for Brisk observatory
Use: Item needed to craft quest key