Just so you don't repeat my silly quest for the lost cave mine:
TThe inside of caves match EXACTLY the outside. If you can walk overland 500 squares to the east to find an other cave, on the inside, both entrances will be EXACTLY 500 squares appart (little chances of being able to walk straight to the other one tho).
So if you enter a cave and have 50% of X metal, it means the mine is EXACTLY 500 squares away... meaning exactly 1 local map (5 minimap)... also meaning you should look for an other cave entrance, seriously.
Best way i found is to find 3 caves and carthograph their external position and remember their metal %. You then copy all the maps to paint (or the GIMP, much better) and draw a 2000 pixel-wide circle (1000 pixel radius) with interior concentric rings.
For example:
1st cave has 11% metal: draw a ((100 - 11) X 20) pixel-wide circle, so 1780s pixel wide.
2nd cave has 30% metal: draw a ((100 - 30) X 20) pixel-wide circle, so 1400 pixels wide.
3rd cave has 46% metal: draw a ((100 - 46) X 20) pixel-wide circle, so 1080 pixels wide.
You will get 3 concentric circles that you just need to superpose on your collated maps and the middle of the circles will be exactly the mine position. You can then scour that area for cave entrances and proceed in the right directly easily
