I'm sure there was a huge amount of superstition surrounding the mines, I don't know why there was so few artefacts that we would expect to find as ritual offering found but here's a little of what Francis Pryor has to say about Great Orme-
"We cannot escape ritual and ideology even down a mine. In fact I'm inclined to say 'especially down a mine' . . . I think it highly unlikely that people ever entered a mine – even a relatively shallow surface mine – lightly. I image that the spiritual dangers that were thought to lie below the ground were vastly more frightening than the prospect of a roof collapse. More likely the two would have been considered interrelated. At Great Orme and elsewhere mines have produced evidence for special offerings of one sort or another. Even the shallow surface working at Great Orme produced large quantities of animal bones, not all of which could have been used as tools . . "

-Chris