Should feasibility work confirm this, Kwale could continue production until mid-2024.
The capital cost is estimated at US$13.6 million.
Adding life to Kwale comes as the company effectively awaits the green light for developing the world scale, multi-decade Toliara project in Madagascar.
The current hope is for first production from Toliara in 2025.
Shares in Base were trading this week at A30c, capitalising the debt-free miner at $353 million.