- Production up 31 per cent in H1- Output on track to hit guidance- Strong H2 revenues expectedFull-year production guidance at Petra was maintained on Thursday, with the diamond miner upbeat about the upcoming sale of an 'exceptional' 29.6-carat blue diamond discovered at its Cullinan mine in South Africa earlier this week.The FTSE 250-listed firm said that production in the first half ended December 31st 2013 was up 31% year-on-year at 1.64m carats, as it remains on track to hit the full-year output target of around 3m carats. The company also maintained its growth plans to achieve annual production of 5m carats by 2019.Revenue during the six-month period was up 19% at $185.5m with a strong second half expected due to the timing of Petra's diamond tenders and the sale proceeds from the blue diamond expected later this year.Blue diamonds are said to be among the rarest and most highly coveted of all diamonds, Petra said, adding that this particular stone "has the potential to yield a polished diamond of great value and importance".The company said that capital expenditure totalled $85.3m during the first half, down from $92.1m the previous year. Costs, meanwhile, remain "well controlled and in line with guidance".Net debt was in line with expectations at $118.1m, up from $89m previously.Chief Executive Johan Dippenaar said that Petra delivered a "strong" first half: "The rough diamond market has also strengthened over recent months and we expect this firmer market to continue into the second half, when the larger part of our diamond sales for the year take place."BC