Utilize the input text as a context reference, choose the right relationship between Grasberg mine and copper from the options. Options: 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.

At full production, Grasberg mine is the largest gold mine, even though the gold is a byproduct of the copper operations.

Answer: product_or_material_produced