Question again:/
Is it actually possible to get flux on a volcano zone?
I know this is a response to an old question but...
I did actually once get limestone right next to a volcano. Unfortunately the map (yes 4x4!) was unplayable due to some wierd cave thing that had somehow appeared over the ground for some twenty levels, it was some impossible natural construction. Map would load, but when you unpaused the game would crash.
Was a crying shame. Now I keep trying to replicate a playable, similar version, but so far having no such luck.
It is entirely possible to get a good flux stone (like limestone) on the same map as a volcano, especially if you extend the map size. Maps don't have to be square, after all; a 2x8 map might cross more biomes (which is good for this purpose) and is exactly as playable as a 4x4 map.
Even so, you'll probably have to design a custom world with worldgen. I wouldn't call it modding, it really just requires adding more volcanoes to the world to up your chances of finding a volcano next to flux. There are never enough volcanoes in the game under normal cirmcumstances.