What is the relationship between Pebble Mine and copper in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

Before going to Kotzebue, Obama went to Dillingham, home to one of the world's largest sockeye salmon fisheries, where residents are fighting the Pebble Mine copper and gold project that has been proposed by Northern Dynasty Minerals Ltd .

Answer: product_or_material_produced