As part of its ongoing pursuit of supplier responsibility, Apple has initiated an investigation into whether tin from Bangka Island, Indonesia is being mined illegally, as first noted by The Verge.

Apple put forth the region as one of the world’s top tin producers. The company said it went on a “fact-finding visit” after hearing concerns. It subsequently created a working group with the Electronic Industry Citizenship Coalition (EICC) and is helping to pay for a study on activity there.

Among Apple’s suppliers, 249 use tin in the components they provide to the company, and 64 EICC-certified tin smelters have been identified. Apple is also tracking sourcing of tungsten, tantalum and gold.

“We will continue to work to certify qualified smelters, and we’ll require our suppliers to move their sourcing of tin, tungsten, and gold to certified conflict-free sources as smelters become certified,” the company wrote.

Other efforts to source conflict-free materials by Apple include joining the Public-Private Alliance for Responsible Minerals Trade, which is focused addressing issues in the Democratic Republic of Congo.

Apple issued its 2013 Supplier Responsibility Report back in January, noting that it had uncovered a plot by labor agents to hide underage workers at a Chinese factory.

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