had this happen a couple times. after exiting the cave and revisiting they will have turned into the proper stone/ore.
in this case, all mined tiles were iron ochre, the long line of iron ochre you see on the top was all generic cave wall before revisiting. thought it might be because of a natural gallery behind it, but no. walls connecting to the basalt on the right are also all iron ochre, but these were the normal orange colour.