Rio Tinto's carat production in Q3 2018 at the Argyle as well as Diavik mines fell on a year-over-year basis, though production for the year thus far has kept pace with the first nine months of 2017. Production during the three months ending September 30 fell by over 17% to 4.9 million carats from 5.9 million carats, driven by a 19% decline at its 100-percent owned Argyle mine in Australia. Total output from the two mines is down by 2% to 14.1 million carats for the year to date.
The Argyle mine delivered 3.8 million carats worth of diamonds in Q3 2018, down from 4.8 million carats in Q3 2017, "when production was enhanced by the processing of higher grade alluvial tailings," yet Argyle's overall production for the first nine months of the year has fallen by just 1% to nearly 11 million carats. At Diavik - where Rio Tinto shares production with Dominion Diamond Mines at a 60-40 split - carats recovered in the third quarter of 2018 were 9% lower than the corresponding period in 2017, also due to lower grades.
Diavik delivered 1.1 million carats for Rio Tinto during the quarter, down from 1.2 million carats in Q3 2017. Total production at Diavik for the year to date fell by 4% to 3.3 million carats. The A21 project at Diavik, the fourth and newest kimberlite pipe at the asset, successfully mined its first ore in March 2018 and is expected to reach commercial production during the fourth quarter of 2018. Rio Tinto's diamond production guidance for 2018 remains between 17 and 20 million carats.