Rio de Janeiro (AFP) - When most of the world talks about the riches of the Amazon they mean the unique rainforest and so-called lungs of the planet.

But Brazilian President Michel Temer has given the nod to a more literal sense of riches -- mineral extraction -- leaving environmentalists and activists including Gisele Bundchen up in arms.

Temer's decision issued Wednesday scrapped a national reserve in the northern Para and Amapa states that had protected a 17,800 square mile (46,000 square km) area since 1984, when Brazil was still run by a military dictatorship.

The Reserva Nacional del Cobre y Asociados is bigger than Denmark and home to virgin forest, as well as indigenous territories of the Aparai, Wayana and Wajapi tribes.

But it also contains important reserves of gold, manganese, iron and copper -- and Temer believes cash-strapped Brazil should start digging.

Until now, state-owned companies had a right to exploit the resources, but rarely did. Temer's measure will open the door to private business.

Temer's aim with the decree is not just to boost the industry but to bring control over activity that is already being performed by illegal miners who use destructive methods that poison the rivers with mercury.

In addition, Temer promises that the mining will not take place in special conservation areas, only outside. "Our promise is to bring sustainable development in the Amazon, uniting environmental protection with revenue generating for the local population," he said.

But analysts are skeptical that much good can come from a president who leans increasingly on the powerful agro-industrial lobby for his political survival amid swirling corruption scandals.

"The measure is meant to bring economic expansion, but it could bring a huge impact. What price will be paid in such a sensitive area as the Amazon?" asked Ely Paiva, an expert at the Getulio Vargas Foundation in Rio.

- Mining disaster -

The World Wildlife Fund says private mining expansion will risk irreversible damage both to the environment and the indigenous peoples.

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"It's a tragedy waiting to happen," said WWF's director in Brazil, Mauricio Voivodic.

"This can cause deforestation, contamination of rivers and ramp up activities like illegal mining. It's about going back to an old vision of the Amazon as a source of natural resources."

Voivodic pointed to the disaster at the Samarco iron ore mine in the Minas Gerais region in 2015 that killed 19 and sent huge quantities of toxic mud flooding into a major river system.

"This decree is the biggest attack on the Amazon in the last 50 years. Even the military dictatorship didn't dare," said leftist Senator Randolfe Rodrigues, who is planning to challenge the decree in court.

Campaigns on social media are going under hashtags like "SOS Amazonia" and Bundchen has given glamorous weight to the resistance.

"What a disgrace. They're selling off our Amazon!" she tweeted.

Bundchen gets listened to in her native Brazil. In June, Temer told her in a tweet that he was promising to veto laws that would reduce protected areas in the Amazon.

But only days later Temer was told by Norway, a huge funder of measures to protect the Amazon, that it was halving payments in response to Brazil's failure to act against deforestation.