SILold mate said they began pumping tails into an old pit and...

SIL

old mate said they began pumping tails into an old pit and wondered for a week or two where it was all going. Turned out there was heaps of old workings that connected the pit to ELN. had to pull out a drill rig and abandon the mine temporarily until the bosses figure out what to do.

Nearest example (albeit fatal and maybe not that relevant in some instances) was bronzewing where I think 3 guys died from drowning due to a slurry/paste fill wall failure. Since then the mines have been pretty touchy on water/mud/etc inrushes that can trap and kill people, hence ELN being shut for now.

old mate had no idea on when it would be re-opened.
Geologically speaking you can come across aquifers when mining, usual way around it is to pump the water out. So my basic understanding would be to re-direct the tails to somewhere else, pump out the water fully, then re-assess for safety etc.

I've said in the past that ELN would be a winner as it was close to surface and you could truck a heap of tonnes out quick, unlike the other decline. So getting rid of a joint that you can pull a heap of tonnes out quickly must hurt.

DYOR