Shares of the miner were down 3.8% at 23.90 pence by 1405 GMT, lagging the small-cap index which was in the positive territory.
Petra has been struggling to clear its multi-million-dollar debts after it borrowed heavily to revamp the Cullinan facility and began mining a new section of ore last July.
However, Cullinan has been profitable every year since Petra acquired it in 2008 and the mine is expected to generate free cash flow this year.
Sterck said the sale of the diamond, which would flow almost directly to the bottom line, will help Petra Diamonds in its target to turn free cash flow positive this year.
Petra Diamonds last month announced the recovery of a 209.9 carat ‘Type II’ diamond at Cullinan mine, the third recovery of a gem of that size since March.
“With additional higher value stones likely to be sold in the quarter ... pricing for Q4 looks likely to be stronger than forecast,” said Sterck.
Courtesy: Reuters