(IDEX Online) - Lucara says it has revised down its revenue guidance from the Karowe mine, in Botswana, for this year by around a fifth, following the abrupt termination of its sales agreement with HB Antwerp.The Canadian miner is forecasting sales of $160m to $190m, down from $200m to $230m, due to the timing of forthcoming sales of specials over 10.8 carats, which account for around 65 per cent of its total production.Lucara cancelled the 10-year contract with HB in September, blaming a "material breach of its financial commitments".In a news release the company said: "Revisions to diamond revenue guidance reflect changes to the sales mechanism for the rough diamonds larger than 10.8 carats in size following the termination of the company's agreement with HB, combined with global rough diamond market impacts."Revenue for Q3, which ended on 30 September was $56.9m, a year-on-year increase of 14 per cent.A total of 98,311 carats were recovered, up 25 per cent on the same quarter last year. That includes 189 specials (+10.8-cts) with six diamonds greater than 100 carats including three diamonds greater than 300 carats in weight.William Lamb, president and CEO, said: "The third quarter results for the company were very good when considering market dynamics and the current state of the diamond sector. "During this period of market weakness, the company is focusing on operational efficiency and key management positions."Pic shows a 692.3-ct Type IIa diamond recovered in August.