(Reuters) – Australia’s Perth Mint, one of the world’s biggest gold refiners, said it would stop processing metal from artisanal and small-scale miners after allegations that it took gold dug in Papua New Guinea using child labour and toxic mercury.

The Australian Financial Review said last week the mint refined gold worth hundreds of millions of dollars despite concerns from some staff about where it came from.

The mint has said it is confident it acted ethically and in line with regulatory requirements and responsible sourcing rules.

Its chairman, Sam Walsh, said in a statement on Tuesday he had launched an independent review of the checks it makes on suppliers.

“The review will also assess the arrangements with licensed counterparties that may deal with Artisanal Smallscale Mining (ASM),” the statement said.

“Effective immediately as part of this process, the Perth Mint has suspended relationships with all companies and aggregators dealing with ASM.”

The mint is accredited by the London Bullion Market Association (LBMA), whose rules require that refiners do not process gold whose production or trade contributes to human rights abuses, conflict, crime or environmental degradation.

The LBMA encourages refiners to work with gold from small scale miners to give them access to the legal market and improve their livelihoods.

But many refiners are wary of taking such gold because of the difficulty of ensuring it is fully legal and ethical.

The LBMA said on Friday it would investigate the allegations against the mint. If it is found to have violated the LBMA’s rules, it could have its accreditation removed, restricting its access to the market.

The Perth Mint is owned by the government of Western Australia and refines more than 90% of newly mined gold in the country, one of the world’s top gold producers.

(Reporting by Swati Verma in Bengaluru; Editing by Peter Hobson and Emelia Sithole-Matarise)