A July 2018 reserve upgrade to 305,000 ounces of gold delivered mine life visibility of three years.
The company is targeting 400,000oz in reserves in an update to be released early next year.
It comes as Millennium is poised for a step-up in production from 75,000-80,000oz this year to at least 100,000oz next year.
Nullagine already operated at a run-rate of 100,000oz per annum in the September quarter.
A sulphide expansion underway at Nullagine is allowing for the uplift in production.
Millennium business development and technical services manager Michael Poepjes told a Resources Rising Stars lunch in Melbourne this week the expansion initially had capital costs of A$50 million, would add $10 per tonne to costs and take a year to build.
Bringing in another consultant settled on a $15 million capex, $3.50/t increase in costs and three-month build.
Poepjes said the expansion remained on track to be commissioned in the March quarter.
Millennium continues to focus on exploration at Nullagine to extend mine life and increase production.
Only four out of 30 deposits have been tested at depth "because they assumed every one was refractory".
Millennium has three surface rigs and one underground rig working across its 280sq.km tenement holding.
Poepjes also identified opportunities for toll treatment, given the company owns the only mill in the district.
He said Millennium would also consider corporate opportunities, like mergers or acquisitions.
Millennium shares were at A17.5c this morning, valuing the company at $138.8 million. Bell Potter has a price target of 29c, while Hartleys has a price target of 30c.
