DESCRIPTIVE MODEL OF UPWELLING TYPE PHOSPHATE DEPOSITS

MODEL 34c

By Dan L. Mosier

DESCRIPTION Phosphorite sediments from a major stratigraphic unit within a sequence of marine sediments in upwelling areas in basins with good connection to the open sea.

GENERAL REFERENCES Slansky (1980), Sheldon (1964).

GEOLOGICAL ENVIRONMENT

Rock Types Phosphorite, marl, shale, chert, limestone, dolomite, and volcanic materials.

Age Range Precambrian through Miocene.

Depositional Environment Marine sedimentary basins with good connection to the open sea and upwelling, areas highly productive of plankton. Deposition occurs mostly in warm latitudes, mostly between the 40th parallels.

Tectonic Setting(s) Intra-plate shelf, platform, miogeosynclines, and eugeosynclines.

Associated Deposit Types Sedimentary manganese.

DEPOSIT DESCRIPTION

Mineralogy Apatite + fluorapatite + dolomite + calcite + quartz + clays (montmorillonite or illite) ± halite ± gypsum ± iron oxides ± siderite ± pyrite ± carnotite.

Texture/Structure Pellets, nodules, phosphatized shell and bone material.

Alteration None related to ore.

Ore Controls Basins, or parts of basins, favorable for the accumulation of organic rich sediments and for their evolution into phosphorites. Individual beds may be a meter thick or more and may extend over hundreds of square kilometers.

Weathering Limonite and goethite.

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

EXAMPLES

Southeast, USID (Gulbrandsen and Krier, 1980)

Meskala, MRCO (British Sulphur Corp. Ltd., 1980)

Stra Quertane, TUNS (British Sulphur Corp. Ltd., 1980)