The European mining heavyweight has 2,600 mines generating 3.5 billion euros ($3.8 billion) in annual revenue and is the second-largest EU producer of copper and magnesite, but sector specialists believe its potential is largely untapped.

"Spain possesses huge wealth in its subsoil" and "must continue investigating" to quantify it, said Ester Boixereu, a geologist and natural resources specialist at the Geological and Mining Institute of Spain.

Deposits of lithium, cobalt, tungsten, nickel and rare earths have been discovered in the south and west of the country in recent years.

Their strategic value has soared as the green energy and technology races have gathered pace because they are critical in the construction of electric-battery cars, wind turbines and smartphones.

The European Union is anxious to turbocharge production of these resources to reduce its dependence on external suppliers, particularly China, which dominates much of the market for renewable energy equipment.

In mid-March, the environment ministry presented a national mining programme at the behest of Brussels aimed at identifying minerals present in new deposits and existing quarries.

The plan opens a path to reforming a 50-year-old mining law and will "strengthen national and European strategic autonomy" in an "increasingly complex geopolitical context", said secretary of state for energy Joan Groizard.

The sector has long been waiting for such assistance. "Mining is a pillar we neglected for a long time," environment minister Sara Aagesen said in an address to the senate in February.

- Environmental fears -

Around 30 operating requests have been submitted in recent years, notably in the central Castilla-La Mancha region where the company Quantum Mineria has identified rare earths.

In Extremadura in the west, several firms hope to extract lithium, a key material for electric-vehicle batteries.

Some of the applications "are advancing very well" but others "remain blocked", said Vicente Gutierrez Peinador, president of the national confederation of mining and metallurgy businesses.

He pointed to a lack of coordination between levels of government and a "lack of political will" at the regional level, where permits are granted, rather than in Madrid.

That reticence comes from local populations who worry about the environmental impact of mining projects, which sometimes require chemical products to extract the precious metals, raising pollution fears.

They also guzzle huge amounts of water -- a major concern in a country that has endured years of drought and faces increasing desertification and fiercer heatwaves as climate change accelerates.

A bonanza in the sector will "increase the probability of accidents and worsen the environmental and social impact inherent to extractive activity", Friends of the Earth said, denouncing a "lack of transparency" from the authorities.

Mining specialist Boixereu nuanced green groups' criticism, saying mining was now "much better regulated" compared with past operations that paid scant attention to the environment.

Sector representative Gutierrez Peinador believes the new government programme "is going in the right direction" but remained cautious because the corresponding credits have not been announced.