After a decent start, London's FTSE 100 index slipped into the red in the afternoon session, as disappointing gross domestic product (GDP) figures from the US dampened risk appetite.Mining stocks bore the brunt of the selling today, pulling the resource-heavy Footsie down from the four-and-a-half-year high reached the day before.US contracts in the fourth quarterThe world's largest economy saw GDP shrink 0.1% in the fourth quarter of 2012, surprising analysts who had expected 1.1% growth. This was a sharp contrast to the 3.1% expansion seen in the third quarter.While the headline figure does not look good, analyst Peter Newland from Barclays Research gave reasons why it's "not all doom and gloom". He said that the downside surprise was mainly due to two components - inventory accumulation and government defence spending - so when excluding these, "the tone of the report was positive". He said that the relative strength of consumption and business investment "suggests that household and corporate sector demand was resilient in the face of uncertainty over the outcome of the fiscal cliff and in a solid position heading into the new year." That would probably suggest why the negative market reaction (on the FTSE 100 at least) to the report was only modest, especially when you consider the rally seen since the start of the month.All eyes now on the FOMCThe focus now turns to tonight's announcement (at 19:15) by the Federal Open Market Committee after its two-day meeting in Washington. "There was some unrest at the last meeting according to the minutes that were released, with some members suggesting that the programme be wrapped up either in June or at the end of the year," said market analyst Craig Erlam from Alpari. "That is unlikely to happen now, with unemployment remaining stubbornly high and growth far from the levels needed to bring it down," he said.FTSE 100: Resources stocks pull the Footsie lowerMining stocks were weighing heavily on the blue-chip index in London after the disappointing GDP figures from the US dampened the outlook for demand. Antofagasta, which posted strong production results for the fourth quarter this morning, sank after warning about higher copper production costs. Sector peer Polymetal was also lower even though it topped production guidance in 2012. Oilfield services groupPetrofac was another big faller as Europe's energy engineering majors dropped over fears that industry earnings would be lower than expected. The industry-wide drop began after Saipem SpA, Europe's largest energy engineering firm, cut its profit forecast.Tobacco giant Imperial registered sharp falls after saying that its Finance Director is to retire. The company also revealed that operating profits would fall in the first half as "market trends have worsened in a number of key markets including in the EU and Russia". Chemicals group Johnson Matthey was in the red after saying that both sales and profits fell in the third quarter. The firm said that volumes in the Precious Metals division had been hit by Amplats's plan to close mines in South Africa.Advertising and media firm WPP was in demand after Jefferies upgraded its rating for the stock from 'hold' to 'buy'. The broker said that an analysis WPP's largest clients and their 2013 ad budget "looks encouraging" and "with expectations low, we see upside risk". Meanwhile, distribution group Bunzl was a high riser after Numis increased its target price from 1,248p to 1,505p, retaining a 'buy' recommendation.FTSE 250: Imagination Tech jumps after upgrade Chip designer Imagination Tech was a high riser after Morgan Stanley upgraded the stock to 'overweight' and increased its target price from 450p to 570p. The broker said that two key possible catalysts - improved exposure in China and a design win in the next Samsung smartphone - are "not fully priced in".Shares in Phoenix Group, the consolidator of closed life assurance funds, jumped after it announced a 27% hike in its dividend and suggested there was more on the way. Phoenix also announced it had raised £250m through a combination of a placing and an open offer of 50m new shares at 500p per share. Precision tool maker Renishaw fell after warning that it faces tough financial comparators in the second half. Nevertheless, the company carved out a sharp increase in half yearly earnings, after it was boosted by a string of large consumer electronics orders in China.FTSE 100 - RisersBunzl (BNZL) 1,134.00p +2.53%RSA Insurance Group (RSA) 134.30p +2.05%Sage Group (SGE) 331.60p +2.03%Prudential (PRU) 973.00p +1.83%BT Group (BT.A) 250.00p +1.54%WPP (WPP) 990.00p +1.28%Pearson (PSON) 1,192.00p +1.19%Babcock International Group (BAB) 1,032.00p +0.98%Legal & General Group (LGEN) 153.10p +0.92%Fresnillo (FRES) 1,681.00p +0.90%FTSE 100 - FallersAntofagasta (ANTO) 1,169.00p -8.31%Petrofac Ltd. (PFC) 1,615.00p -7.02%Aggreko (AGK) 1,612.00p -5.23%Imperial Tobacco Group (IMT) 2,361.00p -4.26%Johnson Matthey (JMAT) 2,306.00p -4.24%Kazakhmys (KAZ) 736.00p -3.98%Evraz (EVR) 291.20p -3.54%Anglo American (AAL) 1,885.00p -2.31%Wood Group (John) (WG.) 805.50p -2.19%BAE Systems (BA.) 341.00p -2.10%FTSE 250 - RisersImagination Technologies Group (IMG) 497.90p +12.77%Phoenix Group Holdings (DI) (PHNX) 630.00p +6.60%Centamin (DI) (CEY) 55.60p +5.10%Oxford Instruments (OXIG) 1,656.00p +4.02%COLT Group SA (COLT) 106.50p +3.00%Savills (SVS) 498.80p +2.93%PZ Cussons (PZC) 384.00p +2.89%William Hill (WMH) 382.30p +2.22%3i Group (III) 272.50p +2.14%St. Modwen Properties (SMP) 236.50p +1.98%FTSE 250 - FallersFenner (FENR) 387.40p -6.20%Ferrexpo (FXPO) 257.00p -5.48%Renishaw (RSW) 1,860.00p -5.10%IP Group (IPO) 124.90p -4.87%Chemring Group (CHG) 275.80p -4.86%Beazley (BEZ) 180.60p -4.85%Kier Group (KIE) 1,345.00p -3.93%Balfour Beatty (BBY) 267.90p -3.81%FirstGroup (FGP) 192.90p -3.50%KCOM Group (KCOM) 71.00p -3.40%BC