| Basis for focus area |
MRDS producers; Jahns and Wright (1951); Foley, Jaskula, Piatak and Schulte (2017). |
| Identified resources |
Historical production of beryllium (beryl), and lithium (lepidolite); production of spodumene, and tourmaline for gemstones. |
| Production |
Stewart mine produced 23,480 short tons of lepidolite between 1900 and 1929 (Jahns and Wright, 1951). |
| Status |
Past mining of gem-quality spodumene, lepidolite, and tourmaline. |
| Estimated resources |
Unknown. |
| Geologic maps |
Jennings and others (2010), scale 1:750,000; Rogers (1965), scale 1:250,000; Kennedy (1999), scale 1:24,000; Kennedy (2000a, b, 2003, 2006); scale 1:24,000; Tan (2000), scale 1:24,000; Tan and Kennedy (1999, 2003), scale 1:24,000; Dibblee and Ehrenspeck (1987), scale 1:24,000; Hernandez and others (2007), scale 1:24,000; Todd and others (2006), scale 1:24,000. |
| Geophysical data |
Inadequate Rank 3 aeromagnetic and Rank 5 aeroradiometric coverage. |
| Favorable rocks and structures |
Visible beryl, spodumene, and lepidolite in pegmatites in Cretaceous granite. |
| Deposits |
Stewart mine (MRDS dep_id: 10286994), Pala Chief Group (MRDS dep_id: 10077343), Rincon pegmatite district (MRDS dep_id: 60000262), Clark Extension prospect (MRDS dep_id: 10286855). |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
Visible beryl, gem quality spodumene and lepidolite. |
| Geophysical evidence |
None. |
| Evidence from other sources |
Jahns and Wright (1951); Hanley (1951). |
| Comments |
Recent 1:24:000 scale mapping covers a sizeable portion of the focus area given its proximity to large urbanized areas and active faults. Future efforts to understand these scattered gem-grade deposits could be focused on geochemistry of the various deposits and age dating. |
| Cover thickness and description |
Pegmatites exposed at surface. |
| Authors |
David A. Ponce, Amy Tuzzolino, Erica Key. |
| New data needs |
Updated geologic mapping, lidar, geochemistry, aeromagnetic and aeroradiometric surveys. |
| Geologic mapping and modeling needs |
Updated geologic mapping. |
| Geophysical survey and modeling needs |
High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys. |
| Digital elevation data needs |
Lidar complete for part of focus area; incomplete over remainder. |
