What is the relationship between 'Pebble Mine' and 'copper' in the context of the input sentence.
Options: position held, legal form, product/material produced, chief executive officer

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 .
product/material produced