The FTSE 100 was in the red in early trading on Thursday as nerves set in ahead of the all-important European Central Bank (ECB) policy decision later on."The day of reckoning has arrived, with the market largely priced for a 25 basis-point (bp) cut in the ECB's main refinancing rate to 0.50%. The latest run of weaker data this week has most likely tipped the balance in our view," said Chief Economist Simon Smith from FX Pro.From an FX point of view, he said that the bigger issue is what happens to the deposit rate, the rate at which funds 'parked' at the ECB are remunerated. Smith said: "In 'normal' times (remember them?), this has been 1.0% below the main rate, to discourage banks from 'parking' funds. If the rate is set negative today (currently it's zero), then this would push the ECB into new territory, for itself and compared to its peers. "The danger is that the ECB punishes well capitalised banks, who could then take money out of the Eurozone, a bigger negative factor for the euro than today's expected cut in the main rate by 25bp to 0.50%. On balance, we don't expect a negative deposit rate today, but it's the main risk to be watching for."Last night saw the US Federal Reserve leave its $85bn-a-month asset purchase programme unchanged, as expected given the weaker-than-forecast economic growth in the first quarter. However, the Fed did acknowledge a more neutral stance on its next move, suggesting that it would ramp up quantitative easing (QE) in response to new data. Previously, the central bank had only said it would reduce QE if necessary.FTSE 100: Updates impress but miners provide a dragIt was a busy morning on the corporate front with a host of heavyweight constituents reporting trading updates and results, most of which were taken well by the markets. However, a weak performance in the mining sector early on kept the FTSE 100 in negative territory.Oil giant Shell was higher as investors shrugged off the news of its CEO quitting and focused on forecast-beating profits in the first quarter.Sector peer BG Group advanced after saying that revenues rose 1.0% despite a slip in production volumes in the first quarter.Financial services group Legal & General was higher early on after hailing record assets, sales and cash generation in the first quarter of 2013 as its UK and US businesses exceeded management's expectations.RSA Insurance also gained after reporting an "encouraging" start to 2013 and saying that it remains on track to hit full-year targets after a good first quarter.Smith & Nephew, the medical technology firm, rose after revealing plans to give back $300m to shareholders via a share buyback. The company posted a 1.0% underlying increase in revenues in the first quarter.Earnings growth slowed slightly for British Sky Broadcasting in its traditionally quiet post-Christmas period, although customer numbers and average revenue per user continued to grow, causing shares in the pay-TV and broadband group to rise early on.Leading the downside was gold miner Randgold which unveiled a sharp drop in first-quarter profits following a decline in sales, production and gold prices. The stock was followed lower by sector peers Vedanta, ENRC and Rio Tinto.Banking group Lloyds was hit after Investec downgraded its forecasts for the stock from 'hold' to 'sell' following the company's first-quarter results this week. The broker said that its profit forecasts for the rest of 2013 "appear deeply underwhelming".Aircraft engine maker Rolls-Royce declined after announcing that the head of its Aerospace business is stepping down. Financial outfit Schroders was also lower despite achieving growth in profits and assets under management at the start of the year.FTSE 100 - RisersBG Group (BG.) 1,118.50p +2.66%WPP (WPP) 1,078.00p +1.32%Sainsbury (J) (SBRY) 387.00p +1.31%Reed Elsevier (REL) 738.00p +1.23%Carnival (CCL) 2,325.00p +0.91%Royal Dutch Shell 'A' (RDSA) 2,211.50p +0.87%Royal Dutch Shell 'B' (RDSB) 2,277.50p +0.82%Legal & General Group (LGEN) 171.70p +0.64%Smith & Nephew (SN.) 741.00p +0.61%Whitbread (WTB) 2,564.00p +0.55%FTSE 100 - FallersRandgold Resources Ltd. (RRS) 4,872.00p -4.66%IMI (IMI) 1,210.00p -2.89%Aggreko (AGK) 1,735.00p -2.47%Schroders (SDR) 2,270.00p -2.37%Melrose Industries (MRO) 244.30p -2.28%Weir Group (WEIR) 2,110.00p -2.13%William Hill (WMH) 414.80p -2.08%Wood Group (John) (WG.) 762.00p -2.06%Vedanta Resources (VED) 1,178.00p -1.92%Aberdeen Asset Management (ADN) 438.00p -1.55%FTSE 250 - RisersNew World Resources A Shares (NWR) 158.60p +5.03%Carillion (CLLN) 278.70p +2.46%Ocado Group (OCDO) 171.20p +1.90%BH Macro Ltd. EUR Shares (BHME) € 21.90 +1.34%Regus (RGU) 164.30p +1.17%Telecity Group (TCY) 935.50p +1.14%NMC Health (NMC) 279.40p +0.98%African Barrick Gold (ABG) 162.00p +0.87%Anite (AIE) 127.20p +0.79%Workspace Group (WKP) 380.90p +0.77%FTSE 250 - FallersImagination Technologies Group (IMG) 355.70p -16.21%RPS Group (RPS) 221.90p -11.59%Inmarsat (ISAT) 698.00p -6.81%Millennium & Copthorne Hotels (MLC) 536.00p -3.42%IP Group (IPO) 154.10p -2.84%Spectris (SXS) 2,075.00p -2.58%Savills (SVS) 569.00p -2.48%BBA Aviation (BBA) 258.90p -2.34%Ophir Energy (OPHR) 399.00p -2.33%Rathbone Brothers (RAT) 1,470.00p -2.33%BC