Middle-Late Miocene Phosphate

Region West, Southwest
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Monterey Formation and age-equivalent formations, such as the Santa Margarita Formation.
Identified resources Historical minor production of uranium.
Production Unknown.
Status Past mining; no current mining or exploration.
Estimated resources None.
Geologic maps Jennings and others (2010), scale 1:750,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Monterey Formation and age-equivalent formations.
Deposits Deposits and occurrences from Chernoff and Orris (2002).
Evidence from mineral occurrences Chernoff and Orris (2002).
Geochemical evidence Monterey Formation and age-equivalent formations such as the Santa Margarita Formation averages 141 ΣREE and 56 ppm ΣHREE (Emsbo and others, 2015). Uranium and related radon issues are well documented throughout the Monterey and age-equivalent formations (Durham, 1987).
Geophysical evidence Unknown.
Evidence from other sources None.
Comments Lumped formations for this focus area included in the unit 'Miocene marine rocks' of the California state geologic map (Jennings and others, 2010).
Cover thickness and description Interest in partially exposed (zero cover) phosphate units and currently mined units in deposits.
Authors Poul Emsbo, John D. Horton, Erica Key.
New data needs Geochemical sampling campaign targeting phosphorites within the Monterey Formation and age-equivalent formations.
Geologic mapping and modeling needs Distribution and isopach thickness of phosphate units. Geochemical analysis of REE content of francolite and P2O5 content of phosphate units to document spatial and stratigraphic variability.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys.
Digital elevation data needs Lidar inadequate.