KEY POINTS:
Fertiliser co-operative Ravensdown could beat rocketing international phosphate rock prices and become self sufficient for decades if reserves in Otago prove economically viable.
Phosphate rock is one of the main ingredients in super phosphate. The international price has soared to just under $767 a tonne.
Ravensdown has agreement from Milton farmers to explore rock reserves on Clarendon Hill.
Based on 1989 data, the estimated 500ha site could hold 34 million tonnes of rock - which would last 22 years.
