TLDR: I have limited knowledge about this and could be wrong so do your own research and feel free to correct me, thanks.
So, from my basic understanding Fireclay mines are typically also coal mines, coal is often found between layers of fireclay. So, fireclay mines are also probably something to stay away from, however i would have to do more research and advice you do your own. Shale is also a mine to stay clear of as its structure and strata are poor. Shale mines are prone to collapsing as the "rocks" are small and flat with little strength or length to create proper layered roofs. Limestone from what I've seen and researched seems to be a good bet as the strata and typical size of "rocks" are larger in length and hight giving more strength and support.
So, from my basic understanding Fireclay mines are typically also coal mines, coal is often found between layers of fireclay. So, fireclay mines are also probably something to stay away from, however i would have to do more research and advice you do your own. Shale is also a mine to stay clear of as its structure and strata are poor. Shale mines are prone to collapsing as the "rocks" are small and flat with little strength or length to create proper layered roofs. Limestone from what I've seen and researched seems to be a good bet as the strata and typical size of "rocks" are larger in length and hight giving more strength and support.
