Papua New Guinea's copper and gold-rich autonomous region of Bougainville plans to stick to declaring independence in 2027.

But eight years after the non-binding vote to secede from the PNG state on a government handshake agreement between the two parties, conflicting remarks are casting doubt on whether independence will be granted to the nation's largest island.

Bougainville, whose independence movement started six decades ago, first declared its own independence in 1975 as the Republic of the North Solomons – 15 days after PNG gained theirs from Australia – in anticipation of joining the British Solomon Islands, who they share close ethnic and linguistic traits over due to the close proximity between each other.

PNG wanted to retain Bougainville from its colonial past over its vast, long-shuttered copper and gold mines and were backed by the Australia at the time.

After years of warring factions for control of the mines between the PNG security forces and rebel separatists from Bougainville, a ceasefire followed by a 2001 peace agreement prevented more killings after 20,000 people were left dead after a decade.

The region that is home to around 300,000 people voted 97.7 per cent in favour of declaring independence during the 2019 referendum.

In 2021, Bougainville's leaders and Papua New Guinea's government agreed on a process that would culminate in a "declaration of independence" for the former province by 2027.

However little more than two years out, the form of independence for the future has not been further discussed.

"The people have spoken," Bougainville president Ishmael Toroama told reporters in Sydney during an investment conference last week.

"The political timeline ends up in 2027."

But essentially, it would be up to Papua New Guinea's parliament to ratify the independence declaration, Mr Toroama admitted.

Papua New Guinean Prime Minister, James Marape, said he could not commit to the Bougainville's deadline, saying it was still subject to the parliamentary process in Port Moresby

"I cannot pre-commit the timeline," Marape told Agence France-Presse (AFP).

Both parties, have at least, agreed there is a need to "clarify" what the parliamentary process is.

"We have established those milestone timelines, and we give respect to the timeline, but, again, as I have said, subject to the parliamentary process," Mr Marape said.

The difference of opinions come down to day-to-day costs to run a new sovereign nation that has to be agreed upon by both governments.

Mihai Sora, of the Lowy Institute, the respected Australian-based think tank, said in a statement the parties may need to appoint a mediator to offer options to resolve their "irreconcilable positions".

Options may include full political independence or something "technically just short of that" offering a path to economic development that is acceptable to Bougainville.

Bougainville's leader said the region was "looking at reopening" the Panguna mine, which at one point accounted for more than 40 percent of Papua New Guinea's exports.

It operated between 1972 and 1989, but anger among Bougainville locals over the distribution of profits triggered an uprising that forced its closure since.

The mine is estimated to hold more than five million tonnes of copper and about 19 million ounces of gold – estimated to be worth worth billions of dollars at current world market prices.

Mr Toroama said there had been "significant progress" this year in redeveloping the mine after an exploration licence was granted to Bougainville Copper Ltd in January.

He also predicted "increased on-site activity" at the mine next year and said there was "abundant opportunity" for investment.

Bougainville must be able to fund at least half of its budget, Mr Marape was quick to tell Agence France-Presse, should the Melanesia archipelago's aspiration of political independence is to be successful to support economic autonomy.

Bougainville was PNG's fiscal war chest for nearly 15 years until 1989 and its closure is what agitated a bloody civil war over revenue from Panguna, the world's third-biggest open cut gold and copper mine at the time.

"We start with economic independence as a fundamental basis because once you have the money, you are able to sustain," Mr Marape said.

Bougainville's internal revenue of seven percent was not sufficient to "get up, get going", he added.

"We need to raise this at the very earliest to about 50 percent of funding," he said.

Toroama said significant progress had been made this year in redeveloping Panguna, with a key copper exploration licence issued in January to Bougainville Copper Limited (BCL), majority-owned by the Bougainville government.

Bougainville Copper Limited has projected revenue of US$36 billion from the mine over two decades, with copper an essential input for renewable energy.

Toroama said his government has to further sign a Memorandum of Understanding for a Rio Tinto and Bougainville Copper Limited partnership for the commencement of works of ageing infrastructure that pose imminent and severe risks to affected communities.

The original mine's strong revenue flows to PNG came at the expense of local communities and the environment, resulting in civil unrest exacerbated, Mr Toroama insisted.

"Bougainville continues to stand out as a lesson, a warning, a reminder of what not to do," he said.