I'm wondering why they would even bother with the second stage...

I'm wondering why they would even bother with the second stage hydrometallurgy test work, the gravity method is producing a concentrate that most base metal miners would be ecstatic with, and with an 18 x uplift in grade with simple gravity methods I think the hydromet second stage would only delay things more and bring in more execution risk. You would think mathematically that with an 18x uplift in grade that there would be an 18x loss in mass so quite a bit of barren tailings/undesirable material to store, but not a fatal flaw, given that nearly all the metals have been removed from this.

The only problem with the eye-watering grades of the gravity concentrates is the peculiar combination of Cu Pb Zn and V all in one concentrate, so maybe some smelters around the world may not be interested in this rather weird but super high-grade polymetallic gravity concentrate. The volumes would be fairly small but the value of this gravity concentrate would be quite high so might support the elongated logistics of getting this exported.