(Sharecast News) - South Africa and Tanzania-focused diamond miner Petra Diamonds generated $79.3m in sales from its first tender of the new calendar year, but gave a cautious outlook for pricing going forward.

The sale of 696.2 thousand carats (kcts) came from Petra's South African operations, with the average price per carat down to just $114, compared with the average price of $140 realised in the financial year ending 30 June.

Compared with the last tender of the previous financial year, in May, like-for-like rough diamond prices were down 4.3%, as a 1-2% increase in diamonds under 2ct was offset by a 14% drop in prices of 2 to 10.8ct diamonds.

Chief executive Richard Duffy said attendance at the August tender was strong but demand was "more muted than we had expected in existing the summer holiday period".

"Macro-economic uncertainties around prevailing high interest and inflation rates have resulted in a more cautious approach from the mid-stream towards holding inventory. Indications are that these rates have now peaked and will start to decline, providing support to our view of improved demand in the medium-term as a result of the structural supply deficit," Duffy said.

"Although demand for lab grown goods increased, this was coupled with further price depreciation that continues to substantially differentiate this market segment from our unique and rare natural diamonds that provide enduring benefit in celebrating life's most significant moments."