Lithium reserves of 5.7 million tonnes at 1.3% lithium oxide mean feed for seven years from open cut and underground mining, with additional resource inventory seen as potentially underpinning a 10-year project.

Core said the addition of underground reserves came "without substantial increases to the start-up capital".

Feasibility work last year on the open cut and plant costed the start-up at A$73 million, with the estimate for two underground developments released today adding an initial $54 million.

Core is estimated to currently have about $1 million cash.

Shares in Core were unchanged at 4.6c in afternoon trade, capitalising the company at $36.5 million.