The breakup fee "is reasonable considering the size of the transaction,'' Asarco said in court papers, giving details of the proposed rules for the auction.
Asarco, based in Tucson, Arizona, filed for bankruptcy protection in 2005 in Corpus Christi, Texas. A judge later stripped Grupo Mexico of control when he appointed independent directors to run Asarco during the bankruptcy case.
Grupo Mexico, Mexico's largest mining company, lost the competition to be a lead bidder in the auction to Sterlite. Grupo Mexico opposes the sale of Asarco, saying it wants to reorganise the unit and pay off its debts in full.
Asarco faces billions of dollars in claims from victims of asbestos-related illnesses and from governments trying to clean up environmental damage.
