A promotional sign adorns a stage at a BHP Billiton function in central Sydney August 20, 2013. BHP Billiton on Wednesday said it will take a $2 billion impairment on its U.S. shale operations – the third writedown in three years. The charge on fiscal 2015 financial results, pushed BHP’s Australian shares to their biggest fall in a week — down 1.7 percent to $26.64. The gas-focused Hawkville field in Texas accounts for the substantial majority of the charge to be included in results for the fiscal year that ended on June 30, which BHP estimates will be around $2.8 billion on a pre-tax basis. BHP announced a $328 million write-down on the Permian field in February and a $2.84 billion impairment on the gas component of the shale division in 2012. The latest charge comes as BHP, the world’s biggest diversified mining company, faces a sharp fall in […]