Originally posted by Migz - DH:

I had something similar happen when I unequipped the wishbone after finding a silver vein's location but without actually uncovering it.

At the time, I suspected that the veins don't actually spawn until we uncover it by breaking through the rock at that spot/depth.

After reequipping the Wishbone, I found that the nearest silver vein was some distance away.

Since then, I always make sure to genuinely uncover, and hit, silver veins before unequipping the Wishbone or leaving the area.

I'm pretty sure the veins are there whether you detect them with the wishbone or not. I've seen the tip of one poking out on the surface, where you could just run across it without even having the wishbone, and there's a youtube video of the same thing out there.