Are there only a total of 2 dark ore caves and no more?look for my post 1572 it has two images the first is the cave you seek
if you leave the starting area and keep heading north past the copper field you will come to an area with a couple of were boars these is more copper and tress etc north past that and in the hill to the west is the cave
its well west of the lake if you go up the hill to the lake you are going the wrong way stay in the plains to the north east of the start area
Also vampire bats seem to be random, sometimes they spawn and sometimes they don't, which allows easier mining.
First time I entered a cave with vampire bats they gave me a jumpscare and instant death.