To start at the end... In my experience, caves are not the best way to find ore. They can be nice to explore and sometimes you find something, and, with the rock exposed, it's quick and easy to use the propick. But it's just too much a matter of luck to find anything while just running around in caves, let alone the ore you were looking for. Sometimes you find massive caves with probably thousands of blocks exposed and there's nothing but some quartz, which would be a lot easier to mine from a cliff above ground or when you just dug down from a spot where you found a lot of quartz stones on the ground.
But to make things a little easier in caves, I'd recommend bringing a lot of torches to light up your way and areas where you want to stay for some time. If you don't do that, drifters can even block your way out of your own brand-new mine that was totally free of drifters when you dug your way down.
And unless you're in a safe spot where they can't reach you, use a longblade instead of a spear. It's much faster.