Small-scale gold mining in the Amazon may not be so small, after all.

Mining within the world’s biggest rainforest is often illegal and contributes to deforestation and disrupts indigenous communities.

Still, Brazil does allow some activity in the region, though artisanal operations have fewer restrictions than large-scale mining.

The latest study by environmental group Instituto Escolhas shows that many small operations are too big to be considered artisanal — and thus should be more closely regulated.

The average investment to hire workers and bring in equipment to dredge rivers and recover gold in the Brazilian rainforest is 3.3 million reais ($690,000), according to a report published Monday by Instituto Escolhas.

That’s enough to employ 75 Brazilian mining technicians for a year. Each of these operations — known as garimpos — can generate annual revenue of around 13.9 million reais, the institute said.

Small land-based mining can bring in 11 million reais.

“Garimpos benefit from legislation that makes few requirements,” Larissa Rodrigues of Escolhas said in a statement. “Therein lies the interest in continuing to maintain the artisanal aura of mining, which has not been a reality for a long time.”