* Cuts annual production target by 2.4 pct to 530,000 tonnes
* EPS rises to 46 cents vs I/E/B/S consensus of 47 cents
* Boosts groups mineral resource tonnage by 25 percent
* Shares fall 4 percent, underperforms mining sector
(Adds shares, more details)
By Eric Onstad
LONDON, Aug 24 (Reuters) - Chilean miner Antofagasta trimmed its annual production target on Tuesday after posting an expected near doubling in first-half earnings per share on higher production and a rebound in prices.
"Group copper production from the three operating mines is expected to be approximately 530,000 tonnes, slightly below the forecast of 543,000 tonnes announced in March," a statement said.
The weaker production forecast is due to delays in launching a mine expansion at its biggest mine, Los Pelambres, following an earthquake in February and lower grades at El Tesoro.
Antofagasta shares slid 4 percent to 986 pence by 0711 GMT, underperforming 1.4 percent fall in the UK mining index.
The shares have climbed by 30 percent since touching a low in early July and have outperformed the mining index by 9 percent so far this year.
Even with the reduced forecast, 2010 output is due to rise 20 percent from last year due to the plant expansion at Los Pelambres.
The group's new mine Esperanza was on track to launch production in the fourth quarter, which together with the Los Pelambres expansion will boost annual output to 700,000 tonnes next year.
PROFIT IN LINE
The London-listed group said earnings per share for the first six months rose 92 percent to 46 cents from 24 cents last year on a 50 percent rise in turnover to $1.76 billion.
Earnings were largely in line with an average forecast of 47 cents from five analysts surveyed by Thomson Reuters I/E/B/S.
Antofagasta declared an interim dividend of 4 cents, up from an interim payout of 3.4 cents last year.
Profits were helped an increase in first-half output of 16 percent year-on-year to 252,900 tonnes and healthy prices.
Average copper prices on the London Metal Exchange in the first half surged by 76 percent compared to last year, when the sector was hammered by the global economic downturn.
"Demand for commodities has remained strong so far this year and while prices could remain volatile, the medium term outlook remains positive," Chief Executive Marcelo Awad said.
Antofagasta also said mineral resource estimates had been completed for its Caracoles and Telegrafo deposits, increasing group resource tonnage by a quarter.
The board had approved spending $70 million to pay for more exploration and pre-feasibility studies for the two deposits, located in the company's key area it has targeted for future growth, the Sierra Gorda district. (Reporting by Eric Onstad; editing by Simon Jessop and Louise Heavens)