Emerald miner Gemfields said a new focus on waste mining and previously reported delays meant production at its mines was down a third in the last year.
However, the trading update also said recent quarters had delivered improving production volumes, a trend the firm was likely to continue in the near term.
In year to the end of June, Gemfields recorded annual production of 21.1m carats, a 36% decrease in the record breaking 33m carats produced in 2011.
Subscribe to MoneyWeek
Subscribe to MoneyWeek today and get your first six magazine issues absolutely FREE
Sign up to Money Morning
Don't miss the latest investment and personal finances news, market analysis, plus money-saving tips with our free twice-daily newsletter
Don't miss the latest investment and personal finances news, market analysis, plus money-saving tips with our free twice-daily newsletter
In the final quarter, the company's reported production growth to 7.3m carats, from 4.9m carats in the prior quarter.
Ore grade for the quarter was 181 carats per tonne, compared to 236 carats per tonne in the previous quarter.
Unit production costs were 57c per carat, versus 85c per carat previously.
"Despite some early minor delays and slightly lower than anticipated full year production volumes, the past few quarters have continued to deliver improving production volumes, a trend that is likely to continue in the near term," said Chief Executive Ian Harebottle.
"This, together with the progress that has been achieve at our Mozambican ruby mine, provides management with the confidence that the coming year will continue to underpin Gemfields' ambitious growth plans."
