Rio Tinto reported a 20% decline in diamond production for the first quarter, as a result of lower output at Argyle, which is approaching the end of its life and is moving to an underground operation. %% In the first quarter of this year, Group production, from Diavik, Argyle and Murowa, totalled 5.0 million carats, compared to 6.3 million carats in the same quarter of 2006. Compared to the previous quarter, Rio produced a total of 9.6 million carats. %% Argyle’s diamond output fell by 33% to 3.5 million carats in the first quarter, from 5.2 million carats in the first quarter of 2006. Compared to the fourth quarter of 2006, production fell by 57%. Rio said variability in feed grade and production rates would continue at Australia’s Argyle mine as it transitions to an underground mine. %% However, at Canada’s Diavik mine, in which Rio has a 60% stake, production soared by 45% in the first quarter, compared to last year's first quarter, as a result of higher grades. Compared to the previous quarter, production increased 4%.