PETRA's Williamson Diamond mine annual output is expected to soar by over 40 per cent in the next three years to 3.6 metric tonnes or 216,000 carats, thanks to a 21 million US dollar (over 33bn/-) investment on expansion drive.

The mine, renowned for its high value 'bubblegum' pink diamonds in Mwadui, Shinyanga, is expected to produce 2.5 Mtpa this year following the completion and commencement of the phase-one project in last year's fourth quarter.

Petra Diamond said on the Trade Update report that Williamson Run-of-Mine (ROM) produced 150,342 carats in the year ending April 2013 against the previous year's 42, 855 carats, following the successful start-up of the newly rebuilt treatment plant. Petra owns 75 per cent of Williamson while the government controls the remaining 25 per cent shares.

Also, contract mining of alluvial diamonds is expected to contribute 14,000 carats in 2013 financial year, with annual review of production levels thereafter. Alluvial are deposits of diamonds that are not mined but founds in riverbed, seabed or shoreline.

The mine lifespan has been extended to 18 years with major resource base at 39.6 million carats. Williamson is an open pit operation, based on the mining of the 146 hectare Mwadui kimberlite.

"Petra's current mine plan for Williamson has a lifespan of 18 years but, given that the Mwadui kimberlite hosts a major resource of 39.6 Mcts, there is potential to extend the Life of Mine (LOM) considerably," the firm said in the statement.

Over the past two years, Petra has been implementing the phase one development programme, which involved substantial reconstruction of existing plant and major pit reshaping work.

Petra, which its overall production upped 21 per cent to 2,668,305 carats this year, said the re‑crush circuit in the plant that was expected to start operations in this year's second quarter will further improve efficiency and ROM grades.

On the costs, the mining firm said, it has achieved a cost of 18 US dollars per tonne during the initial start-up, amid anticipation to reduce cost to 11 dollars per tonne in 2013.

"In the long run, operating costs are expected to drop to 9.5 US dollars per tonne from 2014 and 9 dollars per tonne in 2017 onwards because of increased tonnages diluting the mine's fixed cost base," Petra said. The mine's Phase-Two expansion project, which was initially planned to take the mine to 10 Mtpa, is currently on hold, due to inadequate electricity and water supply.