Situated in the NT's Bynoe pegmatite field Finniss has mineral resources of 9.63 million tonnes.
Core wants to double the expected life of mine at its Finniss project near Darwin.
The offtake deal includes a $1m at-market strategic placement to Xinfeng to fund Finniss.
NT chief minister Michael Gunner says the financial commitment will bring new industry and jobs.
The Grants lithium project gets a green tick of approval.
Core plans to produce 175,000 tonnes per annum of lithium concentrate at Finniss in the NT.
It could cost Core around $73 million to get the Finniss project up and running.
Primero has already started work on a FEED study at Finniss.
Core secures NT's first lithium-focused mineral lease.