HGO won't be able to demonstrate any historical results prior to...

HGO won't be able to demonstrate any historical results prior to option exercise and, if anything, would need to provide an annualised cash flow for the next 2-3 years. However to highlight the quantum change now occurring a quick examination of recent mining costs and waste/ore ratios will provide a good clue.

2015 2016 2017(Q1) 2017(Q2) 2017(onwards)

Mining costs ($m) 81.7 73.6

Waste/ore ratio 5.27 4.34 4.24 4.50 1.80

The high stripping ratio from 2015 to Q2/2017 represents the $60m investment in pre-strip which is a once-off. The lower ongoing ratio may come close to halving mining costs and lead to higher metal production rates. That's a very powerful combination.
Hidden away in the 2016 accounts (regarding asset valuation) is a comment that a 5% improvement in the copper price increases the recoverable amount (of contained metal) by $18m.
It would be nice to see these comments directly from HGO (or published by an external analyst) but that may be wishful thinking.