# Temple fell down sinkhole in mining area, toxic gases

My temple was built near a kaolin surface mine, which is itself topping an old deep mine (where they used to mine radioactive metals, rare earths and possibly other miscellaneous, if need be). This temple was so beautiful that one day the gods took it to heaven, i.e. fell down a sinkhole/big mine shaft (it doesn't matter which) that opened/reopened under it. My MC descends through the mine to investigate the temple, which was sealed in kaolin since the day it fell down.

1) What toxic gases can there be besides CO2? There is no coal.

2) Is this setup geologically passable? If not, what should I tweak?

I can tweak the conditions, and I'm not aiming for 100% accuracy. I'm going for passable in case an expert stumbles upon it.

• You probably need to remember to provide an explanation why the area is not flooded. At least if the temple is not very close to the surface or you are not high in the mountains. – Ville Niemi Mar 21 at 2:45
• @VilleNiemi  why the area is not flooded (moved it) into my answer – Adrian Colomitchi Mar 21 at 3:20
• @AdrianColomitchi Interesting, did not know that. But when I said "remember to provide an explanation" that was what I meant. I wasn't actually asking for the reason or thinking it should be flooded. (Because the question does not actually say where the temple ended up.) – Ville Niemi Mar 21 at 3:34
• @VilleNiemi Interesting, did not know that. neither did I. But I considered the aspect interesting indeed and worth to look for. Then I saw what I found interesting enough to put it into the answer. – Adrian Colomitchi Mar 21 at 3:44

Disclaimer: IANAG(eologist)

Most of the radioactive/rare-earth that I saw are present in the form of silicates, hydroxides, oxides, phosphates, carbonates, borosilicates, vanadates. Haven't seen any in the forms of sulfides or arsenides. So probably no chemically toxic gases.

Radon has a half-life of only 3.8 days, you'd need a lot of uranium/thorium around to get a high enough concentration of radon (in which case, radon is likely the least of your problems)

If the mines are no longer operating, the particulate suspension in the air is going to be low. At the best, such exposures may occur if your character causes a collapse of some dust heaps (assuming dry dust accumulations)

I'd be more worried about exposures to water leeching the rare-earth/radioactive ores around and pooling them in concentrated slurries here and there.

Addressing: why the area is not flooded

kaolinite does not evolve in always damp conditions

While studying soil formation on a basaltic rock in Kivu (Zaïre), they noted how the occurrence of kaolinite depended on the "degrée de drainage" of the area involved. A clear distinction was found between areas with good drainage (i.e., areas with a marked difference between wet and dry seasons) and those areas with poor drainage (i.e., perennially swampy areas). Only in the areas with distinct seasonal alternations between wet and dry was kaolinite found. The possible significance of alternating wet and dry conditions on the transition of allophane into kaolinite has been stressed by Tamura and Jackson (1953).31 The role of alternations between wetting and drying on the formation of kaolinite has also been noted by Moore (1964).32

One can plausibly assume the kaolin deposit was draining through cracks into the bedrock, so there will be at least seasonal opportunities to descend into the old mine galleries.

• Thank you, this is perfect. Both mines operated long ago and the underground one is depleted, or very nearly so. The temple fell down the hole a millennium ago, so humidity conditions could've changed in the meantime from natural or human causes, including river course changes and damming. – geneaux Mar 21 at 4:10