Brazil's government has abolished a vast national reserve in the Amazon to open up the area to mining.
The area, covering 46,000 sq km (17,800 sq miles), straddles the northern states of Amapa and Para, and is thought to be rich in gold, and other minerals.
The government said nine conservation and indigenous land areas within it would continue to be legally protected.
But activists have voiced concern that these areas could be badly compromised.
Around 30% of the overall territory will now be open to mining.
A decree from President Michel Temer dissolved the protected area, known as the National Reserve of Copper and Associates (Renca).
Maurício Voivodic, head of the conservation body WWF in Brazil, warned last month that mining in the area would lead to "demographic explosion, deforestation, the destruction of water resources, the loss of biodiversity and the creation of land conflict".
Brazil's mining and energy ministry has proposed lifting the protections on the reserve to stimulate development.
According to the WWF report, the main area of interest for copper and gold exploration is in one of the protected areas, the Biological Reserve of Maicuru.
There is also said to be gold in the Para State forest, which lies within the area.
The WWF says there is potential for conflict too in the two Indian reserves which are home to various ethnic communities living in relative isolation.
WWF's report said than a "gold rush in the region could create irreversible damage to these cultures".
"If the government insisted on opening up these areas for mining without discussing environmental safeguards it will have to deal with an international outcry."