The withdrawal of accreditation would have hurt the mint, one of the world's largest gold refiners, because big banks that dominate gold trading usually require it, Reuters reports.
The LBMA's guidelines aim to ensure that refiners do not process material whose production or trade contributes to human rights abuses, conflict, crime or environmental degradation.
The Australian Financial Review newspaper said in June the Perth Mint had refined gold from small-scale gold miners in Papua New Guinea who used child labour and toxic mercury.
The mint, owned by the government of Western Australia, has insisted it acted legally and ethically, Reuters reports.
The LBMA said its investigation had revealed no "zero-tolerance non-conformance," and that the Perth Mint would therefore remain on its "good delivery" list of refiners.