PETRA Diamonds Ltd is in advanced talks with De Beers to buy its South African Koffiefontein mine, which it closed down earlier this year. %% Petra said it expected to sign a formal agreement in the near future, adding the mine would add significant production to the group. %% The AIM-listed diamond mining company on Wednesday posted a loss before depreciation, amortisation and foreign exchange movements of $605,315 in the first quarter to September 30, compared to a loss of $698,726 in the three months to June 30. %% Revenue was $4.5 million for the first quarter, compared with $6 million the three months before.