How "gold fingerprinting" helps Brazil crack down on illegal Amazon mining

Illegal gold mining remains one of the greatest threats to the Amazon rainforest, driving deforestation and mercury pollution while fuelling environmental crime. To combat the problem, Brazilian authorities are increasingly relying on forensic science to trace the origin of seized gold and identify whether it was illegally extracted from protected areas.

The technique, which is being explored in one of AP's latest articles, is known as "gold fingerprinting" and  enables investigators to determine whether a newly acquired sample — such as gold seized during a police raid — originated from a national forest, Indigenous territory or another protected area where mining is prohibited.

The work is carried out at the National Institute of Criminalistics in Brasília, where the federal police have established a specialised "gold lab" that collects and analyses samples from across Brazil.

Although the laboratory stores tiny gold flakes in coin-shaped containers, researchers say their true value lies in the information they contain. Each gold deposit develops a unique chemical signature as it forms naturally in rocks or riverbeds, absorbing trace elements such as silver and copper from its surrounding environment.

This chemical "fingerprint" allows forensic experts to determine whether seized gold was mined where its owner claims it originated or whether it was illegally extracted from protected forests or Indigenous lands. If the sample matches data previously collected from a protected area, investigators can identify its true source.

Gustavo Geiser, a federal police forensics expert, said the technique has been under development since 2019 in collaboration with Brazilian universities. Investigators employ technologies including X-ray fluorescence spectrometry, scanning electron microscopy and laser ablation mass spectrometry.

"As we advanced, the forensic examinations became increasingly complex," Geiser said, but the question before them was always the same: "Where did this gold come from?"

If forensic analysis confirms that a gold sample was illegally mined, the findings can be used to support police investigations and potential criminal charges.

Flourishing illegal activity

Environmental criminals operating in the Amazon frequently rely on fraud to introduce illegally obtained products into legitimate markets, not only gold but also cattle and timber. The recent surge in global gold prices has further intensified illegal mining across the rainforest.

According to Amazon Mining Watch, a satellite-based platform that monitors mining activity, approximately 496,000 hectares of rainforest have been cleared for mining since 2023, with more than half of the affected area located in the Brazilian Amazon.

Brazil's Federal Court of Accounts, the country's top audit institution, reported last year that there was evidence suggesting mining permits issued by the National Mining Agency to small-scale miners were being used to legitimise gold extracted from protected areas.

Prosecutor André Porreca, who is leading the investigation, said the permits have become a front used "to launder gold extracted by criminal organizations from Indigenous territories and protected areas."

A separate Greenpeace report published in May described what the organisation calls a "ghost mine" scheme. Drawing on publicly available records, satellite imagery and aerial surveillance, Greenpeace said operators of legally licensed mines declare that tonnes of gold have been extracted from authorised sites, despite satellite images showing little or no mining activity there. At the same time, neighbouring Indigenous territories, where mining is prohibited, display extensive mining operations, suggesting that illegally mined gold is being passed off as originating from legal concessions.

Geiser said the Brasília gold lab has become an important tool in the fight against environmental crime while also helping strengthen confidence in global gold supply chains.

"Being able to state that it [gold] has a legitimate origin and therefore is valid for inclusion in a country's or a bank's financial reserves, I believe provides solidity not only to the market but also to the countries' financial bonds," he said.

By Nazrin Sadigova