The lithium would be used for electric car batteries and is described by the mining company as critical for Europe's transition to green energy.
Portugal's lithium reserves are considered central to Europe's increasing demand for electric cars, but the villagers say it doesn't justify ruining their way of life.
"It would destroy everything," says Aida Fernandes, as she looks across the valley where four opencast pits would border the village of Covas do Barroso in northern Portugal.
Aida, like generations before her, farms cattle in this lush, unspoilt region which has UN Food and Agricultural Heritage status for its landscape and farming traditions.
She deftly manoeuvres a tractor-load of brushwood which she's spent the afternoon cutting from common land owned jointly by the community. Next she spreads the springy branches across the floor of the barn for bedding for her cattle.
Common land is key to a dispute over plans for a new opencast mine - the Barroso Lithium Project - which would produce enough lithium for 500,000 electric car batteries a year over its 14-year operational life.
But three quarters of the mine depends on accessing lithium deposits found in rocks on common land in the area, with the majority owned by the village.
Aida is president of the Baldios - or common land association - which has rejected international mining company Savannah Resource's financial offer to lease the land currently used for forestry and pasture.
The European Union is keen to reduce its dependence on mines in China, Africa and South America for lithium and other raw materials needed for the green energy transition.
The Barroso mine could be one of the first large-scale mines to supply battery grade lithium within Europe and in May Portugal's Environment Agency gave Savannah Resources, which is based in London, the conditional go-ahead.