By Sara Sjolin, MarketWatch

Randgold extends gains after Thursday's rally

LONDON (MarketWatch) -- The FTSE 100 index erased a weekly loss in volatile trading on Friday, as the U.K. benchmark's heavily-weighted resource sector got a boost from firmer commodity prices.

The FTSE 100 rose 0.3% to 6,518.39, setting it on track for a 0.3% weekly advance.

BP PLC (BP) posted one of the biggest gains in the London index, up 3.8% after a judge's ruling cut the maximum penalty it faces for the 2010 Gulf of Mexico oil spill to $13.7 billion. The judge said the fine should be calculated on a spill of 3.19 million barrels, rather than the 4.2 million barrels -- adding up to $18 billion -- sought by the U.S. Justice Department.

Other oil firms were also rising, as crude-oil futures (CLG5) jumped 2%. Royal Dutch Shell PLC (RDSB) gained 0.8%, while BG Group PLC rose 2.4%.

Mining firms, which had declined earlier in the day, trotted higher as metals prices started to turn positive. Glencore PLC (GLCNF) picked up 4.4%, BHP Billiton PLC (BHP) climbed 2.7%, Anglo American PLC added 2.8%, and Rio Tinto PLC (RIO) gained 1.1%.

Randgold Resources Ltd. rose 1.9%, building on gains from Thursday, when the surprise decision from the Swiss National Bank to scrap the franc-euro exchange-rate floor spurred a rally for gold futures.

The Swiss move sent shock waves 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 Thursday. European stock markets were also mostly higher on Friday, with Germany's DAX 30 index briefly moving into record-high territory.

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