DESCRIPTIVE MODEL OF SHORELINE PLACER Ti

MODEL 39c

By Eric R. Force

DESCRIPTION Ilmenite and other heavy minerals concentrated by beach processes and enriched by weathering.

GENERAL REFERENCE Force (1976).

GEOLOGICAL ENVIRONMENT

Rock Types Well-sorted medium- to fine-grained sand in dune, beach, and inlet deposits commonly overlying shallow marine deposits.

Age Range Commonly Miocene to Holocene, but may be any age.

Depositional Environment Stable coastal region receiving sediment from deeply weathered metamorphic terranes of sillimanite or higher grade.

Tectonic Setting(s) Margin of craton. Crustal stablity during deposition and preservation of deposits.

DEPOSIT DESCRIPTION

Mineralogy Altered (low Fe) ilmenite ± rutile ± zircon. Trace of monazite, magnetite, and pyroxene; amphibole rare or absent. Quartz greatly exceeds feldspar.

Texture/Structure Elongate "shoestring" ore bodies parallel to coastal dunes and beaches.

Ore Controls High-grade metamorphic source; stable coastline with efficient sorting and winnowing; weathering of beach deposits.

Weathering Leaching of Fe from ilmenite and destruction of labile heavy minerals results in residual enrichment of deposits.

Geochemical and Geophysical Signature High Ti, Zr, REE, Th and U. Gamma radiometric anomalies resulting from monazite content. Induced-polarization anomalies from ilmenite.

EXAMPLES

Green Cove Springs, USFL (Perkle and others, 1974)

Trail Ridge, USFL (Perkle and Yoho, 1970)

Lakehurst, USNJ (Markiewicz, 1969)

Eneabba, AUWA (Lissiman and Oxenford, 1973)