Ann: Greater Duchess Exploration Update - 41m @ 1.8% Copper, page-142

There are numerous ore bodies at Mount Hope and Lady Fanny and I don't think your assumption of a conical pit is necessarily correct, at least not in every case. I remain hopeful for a long strike length at Lady Fanny and we already know there are parallel ore bodies. Nil Desperandum currently looks like one plunging shoot with some wide halo zones in places.
Also the underground mining, possibly from a decline in each open pit, will add years of ore. We know these shoots can go very deep in the region, for example the Ernest Henry and Eloise mines.
However my calculations were just to gain an insight into the possible open pit depth. I think 200m to 250m deep is my best guess of an open pit maximum depth before underground mining. Calculation may determine a higher profit from a shallower or deeper pit but that is PFS level stuff. Each pit will be different in depth and geometry, for example the narrow lodes at Bourke and Wills may have a very shallow pit.
The JORC and the information provided with it will give a more certain answer to many questions.
Irrespective of the maiden JORC the discovery potential will be high for a few years yet and the JORC resources will be the subject of extensional drilling to grow the tonnes. Nothing is closed off yet and won't be for some time.
Not investment advice. DYOR.