Cota Mine, Gem Hill, Mesa Grande District, San Diego Co., California, USA

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Located near the center SE¼NE¼ sec. 19, T11S, R2E, SBM, approximately 3 miles northwest of Mesa Grande, on the west slope of Gem Hill. Ownership was undetermined in 1957.

The deposit is a pegmatite dike which strikes northwest and dips gently southwest, which ranges in thickness from 2 to 5 feet. Gem minerals were mined from pockets in pods of quartz euhedral perthite pegmatite exposed as discontinuous core segments. Pockets exposed around 1957 were 2 inches or less in maximum dimension and lined with small crystals of quartz, muscovite, albite, and colorless to pale pink beryl. Coarse cleavelandite and lepidolite were present in the dump.

The deposit was discovered in 1907 by Juan Mario Cota, who developed the mine between 1907 and 1910. These workings were reported to have produced garnet, beryl and tourmaline of several shades including amber and wine color. Total output of gem minerals may have been as much as 500 pounds. These workings which were largely overgrown by 1957, consisted of a cut approximately 50 feet long, 10 to 25 feet wide, and 5 to 12 feet deep.

Mineral List

Albite var: Cleavelandite Beryl var: Goshenite var: Morganite

Elbaite 'Elbaite-Schorl Series' 'Feldspar Group' 'Garnet' Lepidolite

'Mica Group' Muscovite 'Perthite' Quartz Schorl

'Tourmaline' 'var: Rubellite' 'var: Verdelite'

18 entries listed. 7 valid minerals.

References