Windhoek - Namibia's diamond mining company Namdeb Thursday announced plans to develop a new onshore diamond mine at its southern diamond fields, expected to produce 45 000 carats a year.The firm has approved funding totalling 280 million Namibian dollars ($36m) for the construction of the mine at Sendelingsdrift, on the Orange River, Namdeb chief executive Inge Zaamwani told reporters."Production is set to start towards the end of 2013," Zaamwani said.It is estimated that the mine will have a seven-year life, producing 45 000 diamond carats a year."However, the stones mined along the Orange River bank at Sendelingsdrift are larger than at our other mining areas, they are around 1.5 carats big," said Namdeb general manager Riaan Burger."The value of the Orange River diamonds is about four times bigger than our other diamonds," he said.Burger said a study had indicated that about 500 million carats' worth of diamonds had been coming down the Orange River over many years."Namdeb has so far probably only mined 100 million carats," he told reporters.The company, which is equally owned by the Namibian government and De Beers, also plans to "push back the sea" to mine the beaches at its onshore sites, where diamond deposits were becoming depleted.According to the financial results released on Thursday, Namdeb registered a net profit of 902 million Namibian dollars in 2011.The majority of its diamonds came from offshore operations.