The manganese mine on Groote Eylandt could make a profit of $500 million over 10-15 years.
About 5 percent of the money would immediately be put into community projects.
The rest would go into a special trust fund.
The fund already holds about $200 million in royalties paid to Traditional Owners by the Gemco manganese mine.
But accountants say it must be built up to $550 million so the interest can be used to keep important social and economic community programs going when mining royalties from the Gemco operation come to an end in about 12 years.
Tony Wurramarrba, chair of the Anindilyakwa Land Council, says islanders must prepare for when mining royalties cease.
The manganese mine is on the small Akwamburrkba Island, formerly known as Winchelsea.
Traditional Owners have given permission for the mining project to go ahead.
It is only one of two mines in Australia owned by Indigenous people.