The overall mineral resource now stands at 14 million tonnes at 1.1% lithium oxide containing 149,300t of Li2O, with the update being the second this year and the third estimate overall.
The updated resource was defined from three deposits — Grandao, Reservatorio and Noa — with the estimate at the Grandao deposit increasing around 87% to 10.3Mt at 1.1% Li2O containing 11,600t of Li2O.
Savannah said it had now reported around 70% of Grandao, with an 6% increase in Li2O grade compared to the February estimate.
The company expect to update the mineral resource estimate further this year, with drilling targeting dip down and strike extensions of the current estimate.
It said it was on track to complete the project's scoping study in the June quarter, with a development decision to be made in early-2019.
Savannah CEO David Archer said Mina do Barroso was shaping up to be a major new European mineral discovery, with the spodumene mineral resource believed to be the largest in Western Europe.
"With the strong growth prospects for lithium ion batteries for electric vehicles and for electricity storage from the grid, this is a critical time to be bringing a project of Mina do Barroso's scale, grade and location, on stream", he said.
"We believe that Mina do Barroso has the potential to be a key piece of Europe's emerging lithium value chain that could help support the shift by European car manufacturers to the production of electric vehicles."
Archer added that there was no current European producer of spodumene concentrate, meaning Portugal could be the first with the development of Mina do Barroso, which already has a mining lease.
"Our focus now is to establish the project's economics," he said.
Savannah's shares rose 9.82% Wednesday to trade at 6.15p (US0.083c).