Demand concerns weighed heavily on the mining sector on Friday after it was revealed that the US economy grew less than expected in the first quarter of 2013.American gross domestic product (GDP) expanded by just 2.5% in the first three months of the year, rebounding after a meagre 0.4% increase in the fourth quarter of 2012 but well below the 3.0% forecast.While the figure is likely to have quashed recent speculation that the Federal Reserve may start to taper its asset purchase programme, it is likely to weigh on the outlook for demand for raw materials.ENRC was a heavy faller, down 6.1% at 271.5p, followed by Glencore, Polymetal, Xstrata, EVRAZ and Antofagasta which were all down around 3.0%.ENRC was extending losses after a tough week for the miner which has seen its Chairman and a number of senior staff leave following a takeover bid by major shareholder Alexander Machkevitch last Friday.To make matters worse, the Serious Fraud Office said yesterday that it has moved to a formal investigation related to corporate governance issues. These such issues also prompted Moody's to downgrade its rating for the stock.RBC Capital was providing more downward pressure on the shares today after cutting its recommendation to 'underperform'.Top performing sectors so far todayElectronic & Electrical Equipment 3,816.41 +0.81%Gas, Water & Multiutilities 5,953.45 +0.56%Food & Drug Retailers 4,576.48 +0.53%General Retailers 2,245.30 +0.50%Life Insurance 5,828.98 +0.43%Bottom performing sectors so far todayIndustrial Metals & Mining 1,779.93 -3.04%Mining 16,577.86 -2.40%Automobiles & Parts 6,275.37 -1.83%Industrial Transportation 2,632.17 -1.82%Forestry & Paper 9,247.21 -1.72%BC