DIAMOND production at Williamson Diamond Mine in Mwadui, Shinyanga has increased by 8.0 per cent but it is still lower than expected. Petra Diamonds which owns the mine said in its financial statement released that the output was below the target due to changes at its treatment plant.

The output increased to 86,309 carats in the first half of the Petra's 2014 financial year that ended last December from 79,910 carats of 2013. It said the results were impacted by the planned downtime to effect certain changes to the treatment plant.The full year production is expected to be in line with guidance, it said in the statement.

Since taking over the mine from DeBeers, Petra has invested extensively on expansion that geared to increase production from 160,000 carats per annum (ctpa) in 2013 to 300,000 ctpa by 2017 financial year.

Petra has recently completed its phase one development programme at Williamson Mine, which involved a substantial rebuild of the existing plant and major pit reshaping work. The production at the Mwadui mine recommenced in the fourth quarter of 2012.

Overall, Petra, which has five-diamond mines in Africa, reported a production increase in the first half of 31 per cent to 1,635,716 carats compared to 1,247,522 carats of similar period in 2013. "Petra remains firmly on track to meet full year guidance of ca. 3.0 million carats... (as) revenue went up 19 per cent to 185.5 million US dollars," it said.

Petra's Chief Executive Officer Johan Dippenaar said the group has delivered a strong first half of the 2014 financial year, with production firmly on track to meet our original full year guidance of 3 million carats.

"The rough diamond market has also strengthened over recent months and we expect this firmer market to continue into second half, when the larger part of our diamond sales for the year take place,

"Increased production and associated cash flows place the Group in a robust position as we continue to deliver on our growth plans to achieve five million carats annual production by 2019."

The Mwadui's Williamson diamond mine is the world's largest economic kimberlite by surface area at 146 hectares in size. It is renowned for beautifully rounded white goods and 'bubblegum' pinks.

The Mwadui kimberlite pipe, upon which the Williamson mine is based, contains a major diamond resource of approximately 39 Mcts.

It is Tanzania's only important diamond producer and despite having been operated continuously since 1940, the pit is only 90 metres at its deepest point due to the large size of the deposit.