According to the Chicago Tribune, “The Iron Lady” proved her mettle this weekend. The biopic opened to a remarkable $280,409 at four theaters — a per-screen average of $70,102. That’s the third-highest specialty opening of the year, after “Midnight in Paris,” “The Tree of Life” and “Tinker Tailor Soldier Spy.” The movie will expand to more theaters January 13. “We couldn’t be happier with the results,” Erik Lomis, the Weinstein Company’s distribution chief, told TheWrap on Monday. “Obviously it’s the number one screen average by a mile for the weekend.”