If the resource size of Zen is much bigger than originally stated,shouldn't the price to attain Zen be much higher as well?

The answer is "depends". Adding more resources now would really only add NPV if the annual projected mie tonnage increased (from the guessed at 50,000 tonnes of graphite per year) as past 20 years out becomes a diluted number. The other factor would be cost, if we added more reserves say at depth what additional mining costs would that entail?