Just dropped a google pin on the site and the area is greener than I expected. Would a lake the size of that pit fill naturally and actually persist? And would it ever be of any use for drinking water?
That particular mine pit will probably be fine (for reasons of geology and tailings treatment, etc . . . " However "
The Berkeley Pit in Butte, Montana, is the cautionary tale everyone wants to avoid.
The 1.6km-by-800m copper mine closed in 1982 and gradually filled with water irreversibly contaminated with sulphuric acid, copper, arsenic, cadmium and zinc from the surrounding rock.
In 2016, some 3000 migrating snow geese were killed when they landed on the toxic brew. The US Environmental Protection Agency (EPA) must pump out and treat the water – forever.
and worth noting that articles such as the one linked above are part of a swelling campaign by land holders and others with leverage to bake clean up costs into resource licencing.
After the geese died, researchers found a microorganism living (and thriving) in the extremely toxic lake. This microorganism was filtering out the toxins 900 times more effectively than any other known organism[1]. The origin of the microbe was the gut of the geese. Radiolab included this story in one episode[2].
Large operations like this, especially those close to coast, generally have to set aside a certain percentage for rehab down the line. Normally part of mining/enviro approvals. The plan needs to be updated every 3-4 years, with updated estimates etc.
Greenbushes is miles away from having to worry about that. I’ve been tangentially involved in the mine designs for the new underground mine coming off the pit, so it’s decades away from rehab.
A few options for old pits I’ve worked on is backfilling with waste material and then capping with earth. Backfilling with treated Tailings and then capping. Or just letting it flood, but putting protections in. Generally they will be liable to manage if for a decade or so after mining is complete. Again all depends on the permit.
Biggest thing you worry about though, especially if you go underground is how to seal it off from other water structures (if required.)
