i'd call it some pretty cool stuff
looks to me like you're having more fun than any rockhound should have by himself, so i hope you have a buddy with you, especially around a sinkhole.
it looks like you are following a vein or layer of travertine with pockets of, lots of pockets, of calcite. Travertine is a calcium carbonate and is sometimes called 'cave onyx', hence your sinkhole. You may be breaking through the roof of a large hollow vug, sometimes called a cave.
if you're at the roof, i wonder what the floor looks like
look up travertine veins and outcrops in Missouri.
and Galena is a good guess for that area.
if you have the opportunity to keep digging i certainly would. if you get to undisturbed areas, go slow and look for all kinds of other minerals in pockets.
like in your second picture, the two dark crystals sticking up in the middle of the 'flow', are they 'terminated' crystals,
are they smoky quartz
and this looks like it might be a good reference for you for all your future rockhounding adventues.
https://www.gutenberg.org/files/59737/59737-h/59737-h.htm#c8good stuff. have fun be careful, and keep us posted.