Mining firms power UK stocks to record high after 50% U.S. copper tariff confirmed

London-listed mining firms bounced on Thursday, shaking off recent losses to drive the U.K.'s FTSE 100 index to a record high as investors assessed the impact of 50% U.S. copper tariffs and stronger Chinese economic data.

Anglo American shares were 5% higher at midday in London, with Rio Tinto and Glencore both up 4.5% and Antofagasta up 3%.

The gains come amid turbulence in the copper market, where prices are at a record high and the premium paid by U.S. buyers over those in the rest of the world is soaring, following this week's unexpected announcement that 50% U.S. duties will be introduced on Aug. 1 — at the top end of expectations.

Anglo American share price.

The news is mixed for the mining giants, which have large operations in key U.S. copper export locations such as Chile, with uncertainty over supply and demand dynamics massively elevated. A broad price spike may be beneficial to producers in the short-term, according to Hargreaves Lansdown's head of money and markets, Susannah Streeter. 

However, the main beneficiaries of higher U.S. copper prices are its major domestic mining companies which sell on Chicago Mercantile Exchange (CME) pricing, according to analysts, which are set to see higher realized revenues.

The U.S. imports just under half its copper, and is widely considered unlikely to be able to ramp up production enough to significantly alter that mix in the short-term, putting continued pressure on prices.

It has been a rough year so far for Europe-listed mining firms, which saw the worst performance among Stoxx 600 sectors in the first half, even as commodities such as gold have rallied. Shares have pulled back from their April lows, but firms including Rio Tinto are down in the year-to-date as poor weather disrupted operations.

The companies are sensitive to expectations for global growth, which have been dented this year by U.S. tariff uncertainty, along with economic signals from resource-hungry China.

Maurizio Carulli, global energy and mining analyst at Quilter Cheviot, told CNBC on Thursday that mining gains were being supported by data showing a rise in Chinese construction machinery sales, a key indicator for the Chinese economy.

News on Wednesday that some members of the U.S. Federal Reserve's voting committee expect interest rate cuts to be appropriate later this year is also positive for the sector, he said.

FTSE 100.

"Finally, there has been somewhat of a technical rebound after the [mining] sector showed a bit of weakness yesterday," Carulli added.

Dan Coatsworth, investment analyst at AJ Bell, flagged wider market talk of a "potential new wave of government stimulus in China," with any support for its giant property sector leading to greater commodities demand.

"Second is a weaker dollar, as that makes dollar-denominated commodities cheaper to buy with other currencies," Coatsworth told CNBC. The U.S. dollar index was slightly lower Thursday, continuing its recent sensitivity to tariff updates.

Coatsworth said that stock markets were meanwhile broadly in a risk-on mood, shrugging off a slew of updates on national tariffs largely viewed as "noise and not facts."

"Trump is throwing out numbers left, right and centre, and investors have begun to dismiss anything that isn't set in stone... that means a shift in focus back to economic data and corporate news flow as key drivers for markets," he said.

Optimism appears to be high among European traders that the EU and White House will strike a framework trade deal before the end of the week.

– CNBC's Spencer Kimball contributed to this story