LONDON, Nov. 20 -- Copper may rise in London on concern about potential threats to supply stemming from labor talks in South America, a survey showed.

    Eleven of 17 analysts, investors and traders surveyed by Bloomberg, or 65 percent, said the metal would gain next week. Five predicted lower prices and one expected little change.

    BHP Billiton Ltd., the world's biggest mining company, said this week it will evacuate its Spence copper mine in Chile after worker sabotage. A 38-day strike over pay has cost 50 tons of output daily at Spence, according to BHP. Workers may strike at the end of the month at Cia. Minera Antamina SA, the Lima-based operator of the world's largest combined copper and zinc mine.

    "Increasing tensions in Latin American labor negotiations add further upside risk to prices," Gayle Berry, an analyst at Barclays Capital in London, said in an e-mail.

    Copper has more than doubled this year, even as inventories in warehouses monitored by the London Metal Exchange have swelled by 24 percent. Stockpiles increased yesterday for a 13th straight day and are heading for a 19th weekly gain.

    "Upward price momentum is strong," Berry said. "We urge caution over trading against the trend, which is strong enough to shrug aside continued stock increases and less impressive macro data."

    Copper for three-month delivery was up 4.4 percent this week at $6,807 a metric ton at 5 p.m. yesterday on the LME.

    The weekly copper survey has forecast prices accurately in 31 of the past 64 weeks, or 48 percent of the time.

    This week's survey results: Bullish: 11 Bearish: 5 Hold: 1

    (Source: Bloomberg)