Glencore owns 25% of both the Noranda Income Fund and Trevali Mining and controls both companies.  Glencore has an offtake agreement with Trevali whereby they purchase all of Trevalie's zinc concentrate at a price that is based on benchmark treatment charges which are currently near $300 per tonne.  Glencore also has a supply agreement with Noranda that is based on spot treatment charges which are currently around $100 per tonne.
Some of Trevali's zinc concentrate production goes to Noranda via Glencore as middleman.  Thus, at current treatment charges, Glencore  pockets $200/tonne and both Noranda and Trevali shareholders get screwed.  This has been going since Noranda's original supply agreement with Glencore expired 4 years ago.