Watters, W.A. 1968 Phosphorite and apatite occurrences and possible reserves in New Zealand and outlying islands. Lower Hutt: New Zealand Geological Survey. Report NZGS 33 15 p.
Abstract: Apart from numerous records of phosphorite nodules and occasional thin phosphatic bands, all of which are small, only three occurrences of phosphorite on land are known, namely at Clarendon, East Otago, Tioriori on the north coast of Chatham Island, and on Manihiki and Pukapuka Atolls in the Northern Cook Islands. Clarendon has been worked in the past, with the production of nearly 150,000 tons of medium-grade phosphate averaging about 24% P2O5 and nearly 22,000 tons of low-grade phosphate averaging about 10.5% P2O5. The following reserves are indicated: 1) about 50,000 tons of medium-grade rock, found in several distinct blocks; 2) about 100,000 tons of low-grade rock, also in separate blocks; 3) a very large deposit of sand, possibly amounting to 230,000,000 tons, averaging 3% P2O5. The medium and low-grade rock indicated can be regarded only as a short-term emergency reserve should overseas supplies of phosphate fail. The sand is of too low a grade to be used, but constitutes a very large potential reserve for the future if economic benefication methods could be developed to upgrade it. The Tioriori deposit on Chatham Island contains about 100,000 tons of rock averaging 10% P2O5, but is not regarded as economic, even for local use. On Manihiki and Pukapuka Atolls in the northern Cook Islands the best samples contain up to 28.4% P2O5. At the most a few hundred thousand tons of phosphatic limestone are present, and under existing conditions the deposits are not considered to be economic. Submarine phosphorite nodules have been found in several places on the Chatham Rise between Banks Peninsula and the Chatham Islands. A substantial potential reserve of phosphate is probable in this region. No concentrations of primary igneous and metamorphic apatite are known. (auth)