While initially planning a standalone tailings operation, New Century now plans to head underground as well.

All environmental approvals are in place for underground mining and long-lead items ordered, with most underground equipment already secured.

New Century plans to acquire a mining fleet through hire purchase arrangements, with Queensland Mining Rebuild Centre to provide the initial underground fleet from its Queensland workshop.

GR Engineering Services has finished front-end engineering and design work and progressed to an engineering, procurement and construction contract for a 1 million tonne per annum ball mill, with construction 86% complete.

The ball mill will be hooked up to Mount Isa's grid supply, which cuts out diesel costs.

According to a recently released optimisation study, branching out from just tailings will reduce both operating and all-in sustaining costs, with metallurgical improvements and flow sheet modifications leading to increased metal production.

Based on current prices, a $78.1 million project would have pre-tax net present value of $246 million and internal rate of return of 101%, with payback in 2.1 years.

Lead metal in-concentrate production would hit 36,000 tonnes per annum, containing 1.07 million ounces of silver, while zinc metal production could be as high as 30,500tpa.

Operating costs of about 95c per pound are 26% lower than for a tailings only operation, while all-in sustaining costs of $1.28/lb are 20% lower.

New Century managing director Patrick Walta said the optimisation study also reinforced the highly value-accretive potential of in-situ development at Century.

"The results underscore the significant near-term opportunity available via the development of Silver King and East Fault Block that will open up the avenue to continue the utilisation of about $2 billion previously invested in infrastructure at Century to 2030 and beyond," he said.