You can found not only yeasts but also black yeasts and many other rock inhabiting fungi. There is lot of articles devoted to this subject. We investigated bacterial biofilms in the arsenic mines. My friend found ca 300 species of bacteria creating this biofilm!
Ohh great to hear that, Iam looking forward for such isolates of biotechnological importance... would love to read your papers as well as your friends' on such Yeast and bacterial biofilms