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Randgold Resources shares fell sharply from record highs after the miner said it had endured one of its “toughest quarters in years”.

The Africa-focused gold miner has been one of the beneficiaries of renewed investor interest in precious metal stocks this year, buoyed by gold’s perceived status as a haven from economic turmoil.

But Randgold said operational issues at two mines led to a fall in production in the second quarter of the year. Net income fell 8 per cent quarter on quarter in spite of a higher average gold price.

Shares in the company fell more than 11 per cent in morning trading in London.

The FTSE 100 miner said it expected to meet its targets for the year, which include producing at least 1.25m oz of gold, after production of 573,000 oz in the first half.

“All our teams have been reworking and optimising their mine plans to ensure that we end 2016 within guidance,” said Mark Bristow, chief executive. “We’re intensifying our focus on critical operational issues to ensure that we deliver a substantial second-half improvement.”

While Randgold did lift gold sales 2 per cent quarter on quarter, production fell 4 per cent on the same basis after a mill breakdown at Tongon in Côte d’Ivoire and lower grades and recoveries at Kibali in the Democratic Republic of Congo. Costs per ounce of gold recovered rose as a result.

Net income for the first half of the year was $123m, 11 per cent up on the same period in 2015.

The miner’s targets for this year also included keeping its cash cost of production under $630/oz. In the first half of the year cash costs were $687/oz.

Before Thursday’s results Randgold’s shares had risen 35 per cent in the past three months and more than doubled this year. They surged after the UK voted in favour of leaving the EU in June.

Tyler Broda, analyst at RBC Capital Markets, said in a research note: “The operational momentum at Randgold continues to slow. Although the market was expecting weak performance at Tongon and potentially at Kibali, both of these mines were worse than we had expected.

“The key question for investors today will be how much could the stock derate as we expect consensus forecasts are likely to fall.”