Rio Tinto has reported a drop in output of rough diamonds during 2014, with the major fall being seen in the Argyle mine, where output was down 19% as compared to 2013. Output from Diavik remained flat during the period, and only the smallest of its mines at Murowa reported a marginal increase of 7%.

The last quarter of the year was particularly slow, the miner said, with Argyle recovering 1.813 mn cts (down 43% y-o-y), Diavik producing 927,000 carats (down 25% y-o-y) and Murowa yielding 101,000 carats (down 4% y-o-y).

For 2014, Argyle recovered 9.188 mn cts (down 19% y-o-y), Diavik producing 4.34 mn carats (the same as a year earlier) and Murowa yielding 344,000 carats (up 7% y-o-y).

Analysing the factors behind the results, Rio Tinto made the following observations:

Argyle: Carats recovered during the year were 19 per cent lower than in 2013, reflecting the move from open pit to underground mining and the processing of lower grades as underground production ramped up. In addition, a maintenance shutdown took place during the fourth quarter to implement some improved design modifications to both underground crushers.

Diavik: Production was in line with 2013, with improved mining rates and processing plant improvements offset by the impact of lower grades. Carats recovered in the fourth quarter were significantly lower than in the previous year as improved processing rates have now fully exhausted the stockpiled ore which was processed in prior quarters.

Murowa: Carats recovered at Murowa were seven per cent higher than in 2013 due to increased ore processed.