By Sara Sjolin, MarketWatch

Randgold retreats after Thursday's rally

LONDON (MarketWatch) -- The U.K.'s FTSE 100 index headed for a third straight week of losses on Friday, after a week where oil prices kept up their volatility and the Swiss National Bank shocked markets by scrapping its euro cap.

The U.K. benchmark dropped 0.3% to 6,481.74, setting it on track for a 0.3% weekly loss.

Mining firms weighed on the index on Friday, with shares of Randgold Resources Ltd. off 2%, Rio Tinto PLC (RIO) down 1%, and BHP Billiton PLC (BHP) 0.8% lower.

Randgold Resources posted one of the biggest gains on Thursday, after the surprise decision from the SNB to scrap the franc-euro exchange-rate floor spurred a rally for gold futures. Gold retreated a bit on Friday.

The Swiss move sent shockwaves through financial markets globally, particularly in currency markets, where the euro and dollar dropped significantly against the Swiss franc on Thursday. Equity markets struggled for direction after the decision, but eventually ended higher in Europe, with the FTSE 100 closing up 1.7%.

On Friday, investors were still monitoring the fallout from the Swiss move, but they also turned their attention back to oil ahead of the International Energy Agency's monthly oil-market report, due at 9 a.m. London time. London's major oil companies traded mixed, with BP PLC (BP) up 2.5% after a judge ruled that the company faces a maximum penalty of $13.7 billion for the 2010 Gulf of Mexico oil spill. That was less than the $18 billion sought by the U.S. Justice Department.

Royal Dutch Shell PLC (RDSB) lost 0.5%, while BG Group PLC fell 1%.

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