Phosphorite nodule deposits, with estimated total reserves in excess of 200 × 10⁶ tons, are present at an average depth of 350 m on the crest of Chatham Rise. The rise is a broad submarine ridge about 130 km wide and 800 km long extending eastward from Banks Peninsula on the east coast of the South Island, New Zealand, to slightly beyond the Chatham Islands. Preliminary investigations based on exploratory dredging in 1968 by Global Marine Inc. suggest that 65 × 10⁶ tons of the phosphorite deposits are concentrated sufficiently to be of economic interest. These more concentrated deposits are mainly in an area of about 4,600 sq km centered 560 km from the South Island.

The phosphate content of nodules ranges from 18.6 to 25.4% P₂O₅, averaging 21.5%. Satisfactory superphosphate can be made from the nodules after they are calcined to reduce their high calcite level. The reactivity of the nodules on the Hoffman and Breen phosphate ore solubility scale is a high 10. Pot trials with rye grass by the New Zealand Fertiliser Manufacturers' Research Assoc. Inc. confirmed the agronomic availability of the phosphate suggesting that finely ground Chatham Rise phosphorite also may have

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value as a direct-application fertilizer.

The deposits have considerable potential value for the agriculturally based economy of New Zealand, where per capita superphosphate consumption is the highest in the world. Current annual consumption of phosphate rock, wholly imported, is about 1,300,000 tons, increasing annually by about 10% during the past 20 years.

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