After a tentative start, the FTSE 100 was firmly in positive territory by Thursday lunchtime, extending its recent winning streak to a fourth day despite some steep falls in the heavyweight mining sector.Renewed optimism regarding the Chinese economy has driven markets higher in the past few days, along with aggressive monetary easing measures in Japan. Since the start of the week, London's benchmark index has gained over 2.5%.A positive start to US earnings season has also lifted sentiment after aluminium producer Alcoa beat profit forecasts in the first quarter on Monday. Investors are now looking ahead to results from banking giants Wells Fargo and JPMorgan Chase due on Friday.Both the Dow Jones and S&P 500 on Wall Street surged to fresh all-time highs last night following the minutes from the last Federal Reserve policy meeting. While some rate-setters called for the central bank to scale back its $85bn-a-month asset purchase programme soon, the meeting took place before the release of March's gloomy employment report. With just 88,000 jobs being added in the US last month, well below the 190,000 increase expected, the consensus seems to be that the Fed cannot risk toning down its stimulus measures for some time yet.Jobless claims in focusThe focus of today's session will be US jobless claims data due later today, which are expected to have fallen to around 360,000 last week, from a surprise jump to 385,000 the week before.Market Analyst Craig Erlam from Alpari said it would be a real boost if the figures comes in below 350,000 this afternoon given the recent "dire" labour-market figures."A figure below here would suggest that last week's jump was just a blip and that labour market in the US is still improving," he said. "On the other hand, if we see another miss this week, it could be seen as confirmation that the US is facing a slowdown in the second quarter, which will weigh heavily on the markets. Expectations are currently for 365,000, which by recent standards is still pretty high."FTSE 100: EVRAZ and ENRC provide a dragSteel group EVRAZ dropped early on after saying that it has decided to forgo a final dividend for 2012 after suffering a 31% drop in earnings as metals prices fell.Mining peer ENRC was also a heavy faller on rumours that its Chairman Mehmet Dalman could resign over disagreements with other executives.Resource stocks on the whole were under pressure early on with Fresnillo and Glencore also among the worst performers. Even Xstrata was registering losses despite announcing that its Koniambo Nickel project in New Caledonia has gone into production after producing its first metal this week, a key milestone for the $5.0bn greenfield project.Heading the other way was High Street department store M&S as a strong performance in its Food division offset a weak performance in General Merchandise (GM). Nevertheless, the 3.8% fall in like-for-like GM sales was still better than the 4.5% decline expected by analysts.FTSE 250: Ashmore surged as AuM increasesAsset management group Ashmore was a high riser early on after reporting that assets under management (AuM) increased by 9.4% in the third quarter as it attracted funds from government clients. Sector peer Man Group also rose as a change in its regulatory status meant a $250m reduction in its capital requirements with the FCA. FTSE 100 - RisersMarks & Spencer Group (MKS) 396.00p +3.18%Schroders (SDR) 2,216.00p +2.93%IMI (IMI) 1,264.00p +2.68%Weir Group (WEIR) 2,343.00p +2.63%Burberry Group (BRBY) 1,313.00p +2.58%easyJet (EZJ) 1,117.00p +2.48%Petrofac Ltd. (PFC) 1,464.00p +2.38%Hargreaves Lansdown (HL.) 886.00p +2.25%Sage Group (SGE) 343.30p +2.11%Rolls-Royce Holdings (RR.) 1,122.00p +2.00%FTSE 100 - FallersEvraz (EVR) 190.50p -9.16%Eurasian Natural Resources Corp. (ENRC) 258.00p -4.41%Fresnillo (FRES) 1,280.00p -3.25%Glencore International (GLEN) 350.20p -2.04%Antofagasta (ANTO) 1,011.00p -2.03%Anglo American (AAL) 1,663.00p -1.89%Randgold Resources Ltd. (RRS) 5,240.00p -1.87%Aviva (AV.) 305.30p -1.83%Xstrata (XTA) 1,055.50p -1.77%Polymetal International (POLY) 878.00p -1.68%FTSE 250 - RisersAshmore Group (ASHM) 404.60p +14.00%Man Group (EMG) 105.30p +7.78%Chemring Group (CHG) 274.20p +4.86%Hays (HAS) 97.90p +4.82%Persimmon (PSN) 1,108.00p +4.23%Spectris (SXS) 2,348.00p +4.22%Redrow (RDW) 197.60p +4.00%Elementis (ELM) 257.90p +3.91%Dixons Retail (DXNS) 33.20p +3.75%WH Smith (SMWH) 772.50p +3.69%FTSE 250 - FallersPetropavlovsk (POG) 196.00p -5.95%Kazakhmys (KAZ) 389.50p -5.09%Lonmin (LMI) 285.40p -4.20%RPS Group (RPS) 257.50p -3.41%Salamander Energy (SMDR) 202.90p -3.24%African Barrick Gold (ABG) 196.90p -2.52%Ferrexpo (FXPO) 188.40p -1.98%Centamin (DI) (CEY) 46.48p -1.88%Vesuvius (VSVS) 341.70p -1.70%Mitie Group (MTO) 269.60p -1.35%BC