BOA VISTA (NYTIMES) - From some 700m in the air, the dirt airstrip is just a crack in a seemingly endless ocean of rainforest, surrounded by muddy mining pits that bleed toxic chemicals into a riverbed.

The airstrip is owned by the Brazilian government - the only way for health care officials to reach the Indigenous people in the nearby village. But illegal miners have seized it, using small planes to ferry equipment and fuel into areas where roads don't exist.

And when a plane the miners don't recognise approaches, they spread fuel canisters along the airstrip to make landing impossible. "The airstrip now belongs to the miners," said Junior Hekurari, an Indigenous health care official.

The miners have also built four other airstrips nearby, all illegally, propelling such a rapid expansion of illegal mining on the supposedly protected land of the Yanomami people that crime has grown out of control and government workers are too scared to return.

This is just a small cluster of the clandestine airstrips pushing the illegal mining of gold and tin ore into the most remote corners of the Amazon rainforest.

Carved into the dense, lush landscape, they are part of vast criminal networks that operate largely unchecked because of the neglect or ineffectiveness of enforcement and regulatory agencies in Brazil, including the military.

The New York Times identified 1,269 unregistered airstrips throughout Brazil's Amazon rainforest in the last year, many of which supply a thriving illicit industry that has surged under President Jair Bolsonaro of Brazil.

Mr Bolsonaro has faced constant global criticism for allowing the Amazon to be pillaged during his administration.

The Amazon acts as a giant sponge, keeping tens of billions of tons of carbon dioxide out of the atmosphere. But it has been under relentless assault in recent years - from logging, extensive burning for agriculture, mining and other legal and illegal threats.

Recent research shows that climate change and widespread deforestation are pushing the rainforest to a tipping point that could destroy its ability to recover from such damage.

Since taking office in 2019, Mr Bolsonaro has championed industries driving the rainforest's destruction, leading to record levels of deforestation. He has both loosened regulations to expand logging and mining in the Amazon and scaled back protections.

Mr Bolsonaro has long supported the legalisation of mining on Indigenous land. He even visited an illegal gold mine on what was supposed to be protected territory, publicly signaling his support for illicit activities in the Brazilian Amazon.

"It's not fair to criminalise wildcat miners," Mr Bolsonaro told supporters outside his home in Brasília, the capital, last year.

On Yanomami land alone - about 97,100 sq km or roughly the size of Portugal - law enforcement officials estimate that 30,000 miners are working illegally on territory protected by the government.

Yet there is little enforcement.

In recent years, their numbers have surged, causing deadly clashes, the displacement of Indigenous communities, swift deforestation and destruction to the land and rivers, with staggering levels of toxic mercury now found in the water.

Many of the 1,269 unregistered airstrips that The New York Times identified have enabled aircraft to land in areas rich with gold and tin ore that are otherwise almost impossible to reach because of the thick rainforest and hilly terrain.

While the role of air traffic in illegal mining has been well-documented, The Times examined thousands of satellite images dating back to 2016 to verify each airstrip and compile the most comprehensive picture yet of the illegal industry's scale.

The Times analysis found at least 362 - more than a quarter - of the airstrips are within 20km of wildcat mining areas, a form of mining that is heavily dependent on highly toxic mercury.

About 60 per cent of those airstrips are on Indigenous and protected lands where any form of mining is forbidden.

The hundreds of other airstrips identified by the Times often support illegal mining operations from greater distances, or are used by drug traffickers or by farmers to spread pesticides.

Beyond that, miners also illegally use or have seized dozens of government airstrips that officials rely on to access remote communities.

"Our perception is that without airplanes, there wouldn't be mining in the Yanomami land," said Matheus Bueno, a federal prosecutor based in Boa Vista, the capital of the state of Roraima, where part of the Yanomami land sits.

From 2010 to 2020, illegal mining on Indigenous lands grew by nearly 500 per cent, and on conservation lands by 300 per cent, according to an analysis by Mapbiomas, a Brazil-based collective of climate-focused nonprofit organisations and academic institutions.

The mining operations have also divided Indigenous groups because some work with the miners while others oppose them. Earlier this year, a fight broke out among two groups, leaving two men dead and five others wounded.

But what most alarms health officials is the mercury used to separate gold dust from riverbed mud, which is poisoning the water and fish the community relies on. Mercury poisoning can impair children's development and attacks the central nervous system, causing a range of health issues from loss of vision to cardiovascular disease, according to a report by Fiocruz, a public health care research institute.

A recent government analysis of water collected from four Yanomami rivers found mercury levels 8,600 per cent higher than what is considered safe for human consumption. "The destruction in some communities is total," Mr Hekurari the health official said. "Mining is everywhere."

Once a lucrative mining spot is identified, more miners arrive carrying supplies to carve out a rudimentary mine. Airstrips are then built in areas rich enough in minerals to support expensive aerial supply chains. "This is how they gain scale," said Gustavo Geiser, a forensics expert with the Brazilian Federal Police who has worked on several illegal mining cases.

The gold is then sold to buyers, some of them unlicensed, who transfer it to smelters in Brazil and abroad for refinement. It then often ends up in banks around the world and in products, like phones and jewellery.

Wildcat mining can be legal, but much of it is carried out without the required environmental permits or in protected areas where it is forbidden. As part of a broad investigation last year into illegal mining on Yanomami land,

Brazil's environmental protection agency, IBAMA, and the federal police seized dozens of planes and helicopters and revealed the inner workings of the logistics that support these operations. The sole distributor of aviation fuel in the state of Roraima was fined for selling to unregistered buyers who ran makeshift gas stations and is still under criminal investigation. Fuel was then carried to airstrips where planes and helicopters were hidden in nearby forest clearings. In May, The Times used a drone to observe one of the airstrips found by the agents and saw two planes being loaded with unknown cargo and several pickup trucks with fuel canisters traveling toward it - an example of how enforcement agencies have struggled to effectively shut down these operations.

The recent expansion of illegal mining across Brazil isn't unprecedented: A gold rush in the 1980s created a crisis much like the one that exists today.

Amid international pressure, the government suffocated most illegal mining by blowing up dozens of airstrips, jailing and extraditing miners and closing off airspace over the Yanomami land for months at a time, according to news reports.

Many law enforcement officials say a similar strategy must be deployed to effectively counter today's illegal mining.

But under Mr Bolsonaro, protection policies have been weakened by an administration that critics say has prioritised unregulated economic development over environmental and Indigenous issues.

On the Yanomami land, the army has three bases for monitoring border activity, one of which is sometimes used to fight illegal mining.

The Times identified at least 35 unregistered airstrips, likely used by miners, within a 50-mile radius of that base.

"The army recognises that the integrity of the border presents itself as a challenge for the Brazilian state, in particular for the security forces," Brazil's army told the Times by email, adding the country shares more than 10,000 miles of border with 10 countries.

Investigating illegal activity on Indigenous lands and federal reserves falls on the Brazilian federal police, but the agency lacks the resources to curb illegal mining activity, according to officials.

The force has a single transport helicopter for the entire country. The military often refuses to support countermining operations, unless agencies with much smaller budgets pay large sums to use its aircraft, according to police officials. Investigations by federal police, environmental agents and prosecutors paint a picture of chaos in the Amazon's airspace.

Planes and helicopters with revoked permits fly undeterred to illegal mines with their transponders off, frequently crossing the border in and out of Venezuela.

Commissioner Paulo Teixeira, who oversees federal police investigations into crimes against Indigenous communities, said the police had little knowledge of how the military monitors illegal air traffic. "Actions to control the airspace would make things easier for us," he said.

Sitting at a recent protest against illegal mines, Christina Rocha remembered her husband, Antônio José, who died the year before when the plane that was transporting him to an illegal mine crashed. His body was found eight months later. "There are so many accidents," she said. "If it was legal, people wouldn't have to take this much risk."

On the Yanomami land, the local Indigenous community sees the growing political power of wildcat miners as a big blow. Today, illegal mining has turned part of a crucial river into a crater of mud.

"The water is like sand," Hércules Yanomami, a local Indigenous leader, said in a phone interview. "We only have a small creek left."