The overall JORC-compliant resource estimate is now 23.5 million tonnes at 1.02% Li2O for 241,000 tonnes of contained Li2O.

CEO David Archer said this was the fourth major increase in the project's resource, which had been achieved in under 14 months. 

The previous increase in September added 44% to the estimate.

The measured and indicated resource was upped by 28% to 13.3Mt at 1% Li2O, representing 58% of the total resource, with an inferred resource of 2Mt at 1% Li2O established at Pinheiro.

All of the mineralisation within the Grandao stage one pit was classified as a measured or indicated mineral resource.

Savannah said its conceptual exploration target of 9-15Mt at 1-1.2% Li2O remained unchanged, which gave Mina do Barroso a potential mineral inventory of more than 30Mt.

"The increasing mineral resource highlights the continued growth potential for the project which is underscored by the exploration target remaining unchanged," Archer said.

"With a potential mining inventory of over 30Mt, we have a long-life asset that can become a secure, long-term supply source of lithium which is a strategic metal for the burgeoning battery and Electric Vehicle industries of Europe."

Recent test work at Mina do Barroso confirmed a low iron deposit of 0.8% Fe2O3, 41% lower than previously thought.

The Savannah board believes there is still significant upside at all deposits to further increase the resource inventory. It is also looking to potentially declare a maiden resource estimate for the Aldeia Quarry prospect.

Savannah's shares (AIM:SAV) have fallen 15.4% in the past six months to the current 5.5p (US7.18c).