So according the to FAQ on this site. You build a mine deck by doing the following:
Creating a Mine Deck using Multiple Sets:
1. Use only one set of passage cards, and pull them out of the map deck.
2. Shuffle the rooms all together.
3. Cut the deck in half.
4. Shuffle the passage cards into half the deck and place that half on top.
That's actually a very elegant solution, we've just been skewing our ratios by having the whole deck with only one set of passages.