The Clarendon deposit was last mined in the 1940s during World War 2, and for the past 18 months Ravensdown has been investigating the quality and quantity of the phosphate rock, including trialling its use in a manufactured superphosphate blend.
Ravensbourne works manager Tony Gray said it was the first time in 70 years a New Zealand fertiliser would be using local phosphate rock - with the industry relying on imported stocks.
After decades of blending mainly imported materials, this is the second launch of a fertiliser product from Otago-based mineral deposits this week.
On Thursday, Featherston Resource's launched its diatomite export business, which comes from $10 million spent on development over 14 years to open a new diatomite quarry in Middlemarch and processing plant near Mosgiel.
Ravensdown chief executive Rodney Green said the first 3000-tonne blend of "Clarendon Gold", 15% comprised of Clarendon phosphate, would go on sale from Monday.
Local farmer Tony McDonnell, who lives in Phosphate Rd, Clarendon, brought the resource to Ravensdown's attention in 2009 and the co-operative has since been working closely with him and other neighbours, including Blackhead Quarries.
Ravensdown has estimated there could be about 200,000 tonnes in the area and it is targeting annual production of about 40,000 tonnes, but it was "early days" and the company "has to work around several areas" to unearth the deposit, Mr Green said.
Ravensdown sold about 200,000 tonnes of superphosphate per year, using imported premium Moroccan rock, some from Vietnam and also from Christmas Island.
Ravensdown would continue to import the balance of foreign rock required, against what can be produced from Clarendon , he said.
While the Clarendon rock did not have the high phosphate content of the premium Moroccan, it contained more iron and aluminium; which was similar to the Christmas Island imported material, he said.
The 450ha South Otago phosphate deposit was one of only two known in New Zealand, the other being on the sea floor, on the Chatham Rise.
Mr Gray said the product had fitted well into the production run and was processing smoothly.
"Its good for the co-operative to take advantage of this domestic phosphate source that is local and cost effective," he said.
By incorporating Clarendon rock into the blend it gave Ravensdown favourable results, physically and chemically, which gave the company the confidence to scale it up into larger production runs, Mr Gray said.
