The general gist of open pit mining is that you need 3.6 to 3.8%...

The general gist of open pit mining is that you need 3.6 to 3.8% combined Zn + Pb to make money at a mining cost of $40/t (including strip). That's around a 10:1 strip.

Metallurgical recovery drops off below 2% Zn or Pb (galena is actually easier to float); the typical tails grade is 0.1-0.3%, so at 3% Zn, you cannot recover much more than 70%. Also, by the by, a head grade of 20% Zn with 95% recovery leaves a tail of 1%.

TC/RC's become a bigger problem for costs, as does pyrite by-product and any penalty from Cd, As, etc, as the penalty is flat and applies to more tonnes of ore per tonne of contained metal.

Ag credits need to be calculated on the Ag in concentrate grade, which we don't know yet. Same for the copper and Au (I did note the Cu and Au up to 1g/t).

There are Zn - Pb mines in Kazakhstan running at 4.4% Zn-Pb at the moment, but they also have Soviet era infrastructure which is amortised, and some subsidies, so they only cover the C2 costs, not the full AISC (what is sustaining capital in a command economy?).

This starts <100m below the deck, and you'd be amazed at how quick you can make a pit pull down on a 300 metre-percent slug of sulphide at that depth and a 10:1 strip.