Utilize the input text as a context reference, choose the right relationship between Rio Tinto Group and London 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.

Producers' shares sank, with Rio Tinto Group dropping to the lowest since 2009 in London and Anglo American falling to a 12-year low.

Answer: headquarters_location