DESCRIPTIVE MODEL OF WARM-CURRENT TYPE PHOSPHATE DEPOSITS

By Dan L. Mosier

MODEL 34d

DESCRIPTION Phosphorites formed in warm currents along the eastern coasts of continents; consist of phosphatic limestone or sandstone.

GENERAL REFERENCES Cathcart and Gulbrandsen (1973), Sheldon (1964).

GEOLOGICAL ENVIRONMENT

Rock Types Phosphatic limestone and sandstone; chert and diatomaceous material may be present.

Age Range Early Cretaceous through Pliocene.

Depositional Environment Basins of structural lows on the flanks of rising domes, at the mouths of rivers and estuaries. Deposition occurs in warm latitudes, mostly between the 40th parallels. Deposits are formed by dynamic upwelling or by the cool countercurrent associated with warm density current.

Tectonic Setting(s) Continental shelf; may be associated with eugeosynclinal rocks.

DEPOSIT DESCRIPTION

Mineralogy Fluorapatite + quartz + dolomite + montmorillonite + kaolinite + calcite ± wavellite ± crandallite ± illite ± clinoptilolite ± palygorskite ± smectite ± collophane.

Texture/Structure Phosphatic pellets and fossil fragments with a carbonate matrix.

Ore Controls Stratigraphic phosphatic horizons within embayments and estuarine environments in proximity to the open sea. Basins on flanks of structural highs (domes, arches, anticlines) are important controls of phosphate deposition.

Weathering Goethite.

Geochemical Signature P, C, U, N, F. Anomalously radioactive.

EXAMPLES

Paulista, BRZL (British Sulphur Corp. Ltd. 1980)

East, north, and south
Florida, USFL

Offshore Savannah, USGA (Zellars-Williams Inc., 1978)