Utilize the input text as a context reference, choose the right relationship between Polyus and mining 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.

However, with the current uncertainty within the mining sector, it seems prudent to stick to companies that are profitable now and, with Petra Diamonds offering stronger growth prospects at a more appealing price than Polyus Gold, it seems to be the pick of the three stocks at the present time.

Answer: industry