That is significantly more than the 2.1mln tonnes which was suggested in a scoping study two years ago.
That study used a cut-off of US$60 per tonne, but consultant QME, which was brought in last year to optimise the mining plan, has suggested a cut-off nearer to US$48.
If a mining plan was developed using that lower cut-off grade, then at a constant 1,000 tonnes per day mill throughput rate as used in the 2017 study, the life of mine would more than double to 18 years.
Should Anglesey bosses choose to up production to nearer 1,400 tonnes per day, the life of mine would still increase to 10 years.
“However, it does have to be noted that by reducing the cut-off, the grade of material that would be delivered to the mill would be lower overall than that used in the 2017 scoping study,” said Anglesey in a statement.
“The economic trade-off between a longer mine life and reduced head-grade will need to be further studied to determine what, if any, would be the net financial benefit. It will then likely require further studies to determine if there is an ‘optimum’ cut-off grade that maximises the financial returns.”
Study results by end of year
QME is still working on the second part of its study, which remains on track to complete by the end of the year.
Funds permitting, that would lead to an upgraded scoping study or a preliminary feasibility study, said Anglesey.
On completion of a feasibility study, QME has the option to undertake the mine's development in return for a 30% stake in the project.
In the same update, Anglesey confirmed that long-serving director David Lean will be stepping down from the board.
Shares were up 9.1% to 1.91p on Thursday.