I love this picture (below) of the Entrance to the Fosterville...

I love this picture (below) of the Entrance to the Fosterville  Mine.

The trucks drive down the road into a huge pit.
The roads descends and winds a bit maybe 800m 'til it comes cave like "entrance"
which is the "black hole" - bottom left.

The trucks would then have maybe a 10 km journey or more winding downwards underground.
The Swan Zone is about 1,000m down so 10km is about right.
The trucks first drive through the Old Oxide Gold Mine "Pit" that Perseverance created.
The Pit (Perseverance Mine) produced less than 200,000 oz of Gold.

Way Below the Pit is where the Sulphide Gold is located - the Bonanza Gold.
They have already mined something like 5m oz of this Gold, have Reserves of about 2.5m Oz
and probably have much more than that as yet 'undrilled" and waiting to be found.

So that little black hole which is the entrance leads to a Mine that will probably have
(including had) something like 20M oz of Gold, maybe 30M, maybe more.
They have only gone down to about 1200m or maybe a bit  more with drilling.
The Gold Zone is believed to go down to beyond 5km - so anybody's guess above 20m Oz.

So I reckon that is a fascinating 'little black hole" bottom left in the Pic.