The company, which owns the Cullinan mine that has produced the two largest diamonds in the British Crown Jewels, said output and revenue will be lower than market expectations.
Petra Diamonds Mining News
The target group was the the top diamond consumer in 2015, a year in which most commodities plummeted, hitting the mining industry very hard.
The miner is confident in the long term outlook for the diamond industry and it expects is to be cash flow positive in the second half of the current financial year.
The diamond will be offered for sale in Johannesburg later this month.
Output rose 16% to 3.7 million carats, which puts Petra on track to hit its long term annual target of 5 million carats in 2018, a year earlier than planned.
It was found at Petra's Cullinan mine in South Africa, which has yielded several massive gems, including the largest rough gem diamond ever discovered.
The 121.26-carat white rock is a Type II diamond "of exceptional colour and clarity," according to Petra.
Price tag makes it the most expensive fancy intense blue diamond ever sold at auction.
The 32.33-carats diamond was recovered in November from the firm’s Williamson mine in Tanzania.
The company remains upbeat and expects a better performance in the second half, driven by a recovery in diamond prices.
The miners concerted effort to limit global diamond supply is forecast to be offset by stable Russian production, new mines, and production increases by Dominion Diamond and Petra Diamonds.
Rough diamonds sales rose to 7.1 million carats in October through December. This compares with 4.9 million carats of sales in the third quarter.
Debswana, a 50/50 joint venture between De Beers and the government of Botswana, is set to close its Damtshaa mine and scale down production at Orapa.
The sale marks the end of De Beers' century-long diamond mining history in South Africa.
But the company is on track to reach its longer-term target of about 5 million carats of diamond production a year by 2019.
"Blue Moon" is expected to fetch up to $55 million when it goes under Sotheby's hammer on Nov. 11, in Geneva.
The miner said smaller than expected diamonds at its Finsch and Cullinan mines in South Africa have sold at modest prices.
But some believe main challenge will be falling prices and wholesalers difficult access to credit to purchase rough diamonds.
Analysts predict could fetch between $10 million to $16 million.
The “Blue Moon" will go on public display in three weeks' time in Los Angeles, California.
Share price continues to hit all-time highs.
The 122.52-carat blue diamond won't be sold before the end of Petra's current financial year on June 30.
Rock was sold to US luxury jeweller Cora International NY through South Africa-based Golden Yellow Diamonds.
Value of the freshly unearthed rare gem could easily exceed $60 million.
London-listed Petra Diamonds shares were on the rise again Monday after the company revealed Friday it had started selling three of its non-core mines.