California Coast Ranges graphite

Region West, Northwest
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Three past producers (from north to south, Unnamed Location, Skinner Ranch, and Unnamed) are listed as flake (Robinson and others, 2017), Multipart focus area composed of graphite mineral sites surrounded by a 5 km buffer. MRDS includes the same three past producers, one prospect, and several occurrences. Associated with Franciscan Complex (KJfs in Jennings and others (1977) or metamorphic rocks in Horton and others (2017).
Identified resources Historical production of graphite.
Production Unknown.
Status Past mining; no current mining.
Estimated resources Unknown.
Geologic maps Wagner and Gutierrez (2010), scale 1:100,000; Graymer and others (2006), scale 1:275,000; Jennings and others (1977), scale 1:750,000.
Geophysical data Mostly adequate aeromagnetic coverage. Mostly inadequate radiometric coverage. Fair gravity coverage.
Favorable rocks and structures Franciscan Formation.
Deposits Skinner Ranch (MRDS dep_id; 10077828), Black Magic graphite (MRDS dep_id: 10238330).
Evidence from mineral occurrences MRDS; Hamilton (1915); Robinson and others (2017).
Geochemical evidence None.
Geophysical evidence Some magnetic anomalies in the San Francisco Bay Area are related to ophiolite and volcanic rocks.
Evidence from other sources Unknown.
Comments Graphite from the Skinner Ranch deposit (opened in 1894) was shipped to San Francisco for paint manufacture; the output was valued at $9,000.
Cover thickness and description On or near Franciscan Complex rocks and undivided pre-Cenozoic metasedimentary and metavolcanic rocks (Jennings and others, 1977).
Authors David A. Ponce.
New data needs Geologic mapping, geophysics, lidar.
Geologic mapping and modeling needs Detailed geologic mapping.
Geophysical survey and modeling needs Aeromagnetic, gravity, and aeroradiometric data. Graphite is unusually highly conductive and magnetotelluric surveys may be useful.
Digital elevation data needs Lidar complete over part of the scattered focus area; not available in the rest.