BHP Billiton (NYSE: BHP ) reported a 58% drop in its first-half profit. The company also announced the retirement of its chief executive Marius Kloppers. BHP Billiton's first-half profit declined to US$4.24 billion. BHP Billiton shares closed at $80.46 yesterday. (c) 2013 Benzinga.com. Benzinga does not provide investment advice. All rights