Markets opened slightly higher on Thursday morning after falling to a two-week low the day before as concerns about the global economy continue to unnerve investors.The FTSE 100 slumped 2.0% on Wednesday after the OECD slashed its global growth estimates and the International Monetary Fund reduced its forecasts for China. Meanwhile, volatile trading in Japan endured overnight with the benchmark Nikkei index dropping over 5.0% as the yen continued to strengthen against the dollar.Also a cause for concern for markets has been the increased speculation that the Federal Reserve will begin to taper its quantitative easing (QE) programme soon. Boston Fed President Eric Rosengren threw more weight behind the argument yesterday by saying that the recovery may be strong enough in a few months' time to allow the central bank to scale back asset purchases."It seems policy makers are of the belief that the strength of the US economy is significant enough to justify at least thinking about ending stimulus measures," said Financial Trader Shavaz Dhalla from Spreadex."In most situations, one would expect investors to be thrilled that one of the world's largest economies is firmly on the path to recovery. However, it seems investors are more preoccupied with the consequences of ending QE rather than rejoicing in the fact that the US economy is showing positive signs of growth."The American economy will likely be in focus once again today as markets await the latest figures for US gross domestic product (GDP) this afternoon, as well as jobless claims and pending home sales. Elsewhere, eyes will be closely watching a bond auction in Italy and consumer confidence figures in the Eurozone this morning.Miners provide a lift early onMining stocks were making gains this morning as metals prices advanced. Randgold, Polymetal, Fresnillo, ENRC and Glencore Xstrata were among the best performers on the FTSE 100.Tullow Oil was also up despite saying that it has been forced to plug and abandon another one of its exploration wells, this time off the coast of Cote D'Ivoire.B&Q owner Kingfisher was in the red after revealing a 0.4% fall in first-quarter sales as a result of weak consumer confidence and unseasonably cold weather in March and early April.Severn Trent was subdued despite after the utilities company reported an annual profit that slightly missed analysts' expectations.In contrast, Tate & Lyle edged higher after its full-year profits came in ahead of forecasts, "albeit driven by technical influences around a provision release and lower than expected tax and financing charges," said analysts at Investec.FTSE 100 - RisersRandgold Resources Ltd. (RRS) 5,115.00p +3.52%Fresnillo (FRES) 1,124.00p +3.21%Polymetal International (POLY) 678.00p +3.04%Eurasian Natural Resources Corp. (ENRC) 258.80p +2.94%Glencore Xstrata (GLEN) 336.05p +2.53%International Consolidated Airlines Group SA (CDI) (IAG) 279.80p +2.12%Rio Tinto (RIO) 2,912.00p +1.80%Vedanta Resources (VED) 1,303.00p +1.64%Wood Group (John) (WG.) 847.00p +1.62%Lloyds Banking Group (LLOY) 61.47p +1.37%FTSE 100 - FallersTesco (TSCO) 365.85p -1.92%Aberdeen Asset Management (ADN) 465.90p -1.42%BT Group (BT.A) 301.90p -1.15%AstraZeneca (AZN) 3,417.00p -1.06%Croda International (CRDA) 2,513.00p -1.02%Shire Plc (SHP) 2,165.00p -1.01%Marks & Spencer Group (MKS) 468.60p -0.72%Morrison (Wm) Supermarkets (MRW) 276.20p -0.68%Burberry Group (BRBY) 1,494.00p -0.66%Carnival (CCL) 2,222.00p -0.63%FTSE 250 - RisersFirstGroup (FGP) 123.00p +4.24%Kazakhmys (KAZ) 347.80p +4.01%Petropavlovsk (POG) 135.00p +4.01%Brewin Dolphin Holdings (BRW) 238.80p +3.69%ICAP (IAP) 359.50p +2.86%Tullett Prebon (TLPR) 282.30p +2.69%African Barrick Gold (ABG) 142.00p +2.53%Hochschild Mining (HOC) 246.70p +2.24%Ferrexpo (FXPO) 174.50p +2.23%Diploma (DPLM) 558.50p +1.92%FTSE 250 - FallersAshtead Group (AHT) 636.50p -2.00%COLT Group SA (COLT) 107.50p -1.56%Menzies(John) (MNZS) 702.50p -1.47%New World Resources A Shares (NWR) 106.50p -1.30%Templeton Emerging Markets Inv Trust (TEM) 614.50p -1.29%Go-Ahead Group (GOG) 1,494.00p -1.06%Renishaw (RSW) 1,773.00p -1.06%Carpetright (CPR) 615.50p -1.04%Berkeley Group Holdings (The) (BKG) 2,107.00p -0.99%Persimmon (PSN) 1,230.00p -0.97%