The -listed miner said the "exceptional" 29.6 carat blue diamond it unearthed at the would lead to strong second-half revenue.
Petra, which has seven producing mines in and one in , reiterated its 2014 production guidance of about 3 million carats for the year ended June 30, 2014.
Revenue increased to $185.5m in the six months ended December 31, from $156.3m a year earlier.
Petra said it produced 1 635 716 carats during the period, up 31% from the year earlier.