...+ U.S.-based iron ore producer Cliffs Natural Resources Inc. has announced a private debt exchange offer for its second-lien and senior unsecured debt. + The exchange of up to $710 million of aggregate principal would be funded by newly issued 8.00% 1.5-lien senior secured notes due 2020. + Holders that tender their notes will receive compensation substantially below the original principal amount. + We are lowering our corporate credit rating on Cliffs to '##' from 'B' and our issue-level ratings on the company's second-lien notes to '##' from '##-' and on its senior unsecured notes to '##' from 'B'. + The negative outlook reflects the potential that we would lower the corporate credit rating to '##' and the ratings on the affected issues to 'D' if the exchange proceeds. DALLAS (Standard & Poor's) Jan. 28, 2016--Standard & Poor's Ratings Services said today it lowered its corporate credit rating on Cleveland-based iron ore producer Cliffs Natural Resources Inc. to '##' from 'B'. The outlook...