An Assessment of Substrate Phosphorite Resources in the Hawaiian Eez.
Arvidson RS; Wiltshire JC; Yeh H
For Reference Only At Bureau Libraries Contract No G1185128-1506 (G1185128-1506):8 pages
A preliminary assessment of the phosphorus content of the substrate underlying ferromanganese crusts was undertaken for selected seamounts in the Hawaiian eez. A total of 18 substrate samples from the Hawaiian eez and 1 from the Johnston Island eez were separated from the attached ferromanganese crust and analyzed for a suite of 27 elements. Values of up to 29.6 pct p2o5 were recorded, well within the range of economic terrestrial phosphate deposits. The majority of the phosphorite substrates contain pebble-sized fragments of weathered basalt set in a matrix resembling a fine- grained carbonate in which the major phosphorite mineral, francolite (carbonate fluorapatite), has partially or wholly replaced the carbonate. It appears that the factors favoring phosphate accumulation are local rather than regional. Phosphatization is correlated with low detrital influx. It is likely that seawater may have been the primary source of the phosphorus. Phosphorus precipitates from seawater episodically during times when ocean circulation or chemical equilibrium favors an increase in phosphate saturation. The phosphate appears to accumulate preferentially on a favorable substrate such as calcium carbonate. If further work confirms this process, then one may expect that phosphate resources are quite widespread in the Hawaiian eez. The current work suggests that the underlying phosphorite resource should be seriously considered as a mining target along with the manganese crusts themselves. Further evaluation of this resource is required.
CP; Final Contract Report;
For Reference Only At Bureau Libraries Contract No. G1185128-1506
University of Hawaii