By Sara Sjolin, MarketWatch

LONDON (MarketWatch)--The U.K.'s FTSE 100 index seesawed around the flat line on Thursday, with optimism over a dovish European Central Bank offset by declines for miners and AstraZeneca.

The FTSE 100 index was flat around 6,539.50, after trading as high as 6,580.21 earlier in the afternoon.

The brief rally came after ECB President Mario Draghi hinted the Governing Council is moving a step closer to full-blown quantitative easing if current measures aren't enough to beef up the sluggish eurozone economy.

The Bank of England offered no surprises, keeping its key lending rate at record low of 0.5% and the size of its bond portfolio unchanged at 375 billion pounds ($599 billion).

Adding pressure in London, shares of AstraZenaca PLC dropped 0.8%, after the drug maker reported a sharp decline in third-quarter profit.

Miners were also falling as iron-ore prices sank to a near 5 1/2 year low. Shares of Rio Tinto PLC (RIO) dropped 1.1%, Anglo American PLC fell 0.5% and Antofagasta PLC lost 0.6%.

RSA Insurance Group PLC lost 3.7% after the company posted a decline in net written premiums.

On a more upbeat note, shares of Randgold Resources Ltd. jumped 7.7% after the gold producer reported a rise in third-quarter profit, as higher output offset lower gold prices.

In U.K. data news, the Office for National Statistics said production rose 1.5% in September, year-over-year, a tad lower than consensus forecasts, according to FactSet.

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