Utilize the input text as a context reference, choose the right relationship between 'Pebble Mine' and 'copper' from the options.
Options: legal form, product/material produced, chief executive officer, position held

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