DESCRIPTIVE MODEL OF LATERITE TYPE BAUXITE DEPOSITS

MODEL 38b

By Sam H. Patterson

APPROXIMATE SYNONYM Aluminum ore (Patterson, 1967).

DESCRIPTION Weathered residual material in subsoil formed on any rock containing aluminum.

GENERAL REFERENCE Patterson (1984).

GEOLOGICAL ENVIRONMENT

Rock Types Weathered rock formed on aluminous silicate rocks.

Textures Pisolitic, massive, nodular, earthy.

Age Range Mainly Cenozoic, one Cretaceous deposit known.

Depositional Environment Surficial weathering on well-drained plateaus in region with warm to hot and wet climates. Locally deposits in poorly drained areas low in Fe due to its removal by organic complexing.

Tectonic Setting(s) Typically occurs on plateaus in tectonically stable areas.

Associated Deposit Types Overlain by thin "A" horizon soil, underlain by saprolite (parent rock in intermediate stages of weathering).

DEPOSIT DESCRIPTION

Mineralogy Mainly gibbsite and mixture of gibbsite and boehmite; gangue minerals hematite, goethite, anatase, locally quartz

Texture/Structure Pisolitic, massive, earthy, nodular.

Alteration Aluminous rocks are altered by weathering to bauxite.

Ore Controls Thoroughly weathered rock, commonly erosional boundaries of old plateau remnants.

Weathering Intensive weathering required to form bauxite. Bauxite continues to form in present weathering environment in most deposits.

Geochemical Signature Al, Ga.

EXAMPLES

Australia, Brazil, Guinea examples are reviewed in Patterson (1967)