Fort Cady

Location: California, United States (34.753, -116.418 approx.)

Commodities: lithium; boron; gypsum

Deposit model: closed-basin brine · evaporites · unclassified

Geology

“The main borate deposit area lies between 350 m to 450 m below the current surface. The deposit comprises a sequence of mudstone and tuff. The borate mineralization occurs primarily as colemanite (2CaO 3B2O3 5H2O) in thinly laminated silt, clay and gypsum beds. In plan view, the concentration of boron-rich evaporites is roughly ellipsoidal with the long axis trending N40-50W. A zone of >5% B2O3 mineralization, ranging in thickness from 20 m to 68 m (70 ft to 225 ft), is approximately 600 m wide and 2,500 m long (Figure 4.3 in May 2017 Prospectus). Boron is believed to have been sourced from thermal waters that flowed from hot springs in the region during times of active volcanism. These hot springs vented into the Hector Basin that contained a large desert lake. Borates were precipitated as the thermal waters entered the lake and cooled or as the lake waters evaporated and became saturated with boron. Based on assay results, it appears if mineralization took place in several cycles, resulting in somewhat distinct mineralized horizons.” (Fourie (2018))

Published resource estimates

As compiled by USGS USMIN from the cited studies. Resource classes follow the source; "approximate" flags values USMIN reports as approximations. These are not current company reserve statements.

Recorded production

• Fort Cady, Pilot plant: produced an unstated amount of synthetic colemanite, 1996–2001 (Fourie (2018), Page 6)
• Fort Cady, Pilot plant: produced 450.0 metric tons of boric acid (H3BO3), containing about 79.1 metric tons B, 1987–1988 (Fourie (2018), Page 6)

Exploration and site history

• Resources: “The only by-product reported here is lithium. The exact nature of the lithium mineralization is unclear. It is thought to be associated with the interbedded clays, and a marked negative grade correlation with Boron does exist. In addition, historical assays has intermittent lithium analyses, and by convention non-assayed intervals are assigned a zero grade. Current efforts are under way in determining the leaching potential of lithium from the clays. It should be noted that due to these factors, and to the fact that lithium is reported as a by-product, and thus within the higher grade boron zones, the reported lithium grade is significantly lower than some of the higher grade intersections seen.” (Fourie (2018))
• Active — The first phase of pilot plant operation consisted of 450 t of boric acid production, the second phase consisted of 1,800 t of synthetic colemanite, 1987–2001 (Fourie (2018))
• Discovery — Discovery of the Fort Cady borate deposit occurred in 1964, 1964 (Fourie (2018))
• Exploration — Completed 2 of 6 lithium brine exploration holes to assess the lithium potential for the project, 2017 (Fourie (2017))
• Development — The project was fully permitted for construction and operation, 1994 (Fourie (2018))
• Evaluation — JORC compliant report, 2017–2018 (Fourie (2018))

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.