CEC buys electricity from Zesco in bulk and sells it to mining companies including the local units of Vedanta Resources (Other OTC: VDNRF - news ) , Glencore (Xetra: A1JAGV - news ) and Vale.
Refer to the input text as context and select the correct relationship between 'Glencore' and 'mining' from the available options.
Options: legal form, industry, director/manager, operator