Utilize the input text as a context reference, choose the right relationship between Glencore 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.

CEC buys electricity from Zesco in bulk and sells it to mining companies including the local units of Vedanta Resources , Glencore and Vale.

Answer: industry