(IDEX Online) - Rio Tinto yesterday reported another drop in quarterly diamond production at its Diavik mine, in Canada, down 16 per cent on Q2 2022 to 970,000 carats.It said output was lower because of "the completion of an underground pipe and area of the open pit during the period."In February, Rio Tinto, the world's second-largest metals and mining corporation, announced plans to invest $40m in underground mining that would prolong Diavik's life to early 2026.It said underground mining below the existing A21 open pit operation should yield an additional 1.4m carats.Rio Tinto reported in Q1 that it had recovered 954,000 carats, down four per cent on 991,000 carats in Q1 2022, because of temporary restrictions accessing open pit material.Half-year production (H1 2023) fell 10 per cent from 2.14m carats (H1 2022) to 1.92m carats.Guidance for FY 2023 remains unchanged at 3.0m to 3.8m carats.Rio Tinto became 100 per cent owner of the mine in November 2021, ending a long legal battle with Dominion Diamond Mines over the mine's operating costs and production targets.Pic shows Diavik mine, Canada.