New Mexico Mineral Symposium — Abstracts

Geologically, the Baja Peninsula is a complex mix of the three basic rock types that span the geological time scale from Precambrian metamorphic rocks to Holocene marine gravels and terrestrially derived alluvium. Stretching from Tijuana in the northwest to Calmalli several kilometers north of the boundary between Baja Norte and Baja Sur is a series of Late Jurassic–Early Cretaceous intrusions predominantly granite pegmatites and batholiths. Early to middle Cretaceous sedimentary rocks of marine and continental origin are intermittently exposed
with the intrusive rocks.

A major part of Baja Sur is Miocene to Holocene continental volcanic rocks. The tip of the peninsula is, once again, intrusive granite pegmatites and batholiths of middle Mesozoic age, the same type as the exposures in Baja Norte. Pliocene to Pleistocene fossils are readily exposed in the roadcuts along Mexico Highway 1. These are mainly marine gastropods, pelecypods, and ostracods. Sharks' teeth have also been noted from roadcuts between Ciudad Constitucion and La Paz.

At the northern extreme of the metamorphic and igneous intrusive rocks in Baja Norte, one finds extensive pegmatite deposits, a continuation of the same pegmatites of southern California. These rocks also host gold mineralization. But, the more spectacular gold specimens from Baja have come from the south-central part of Baja Norte, east of Guerrero Negro at Calmalli and El Arco. El Arco is the site of a more recent major copper deposit in the central peninsula. San Felipe is another notable mineral locality in Baja Norte known for its sulfur deposits.

In Baja Sur, the rich copper deposits from the Boleo district of Santa Rosalia are the best known of any mineral occurrence. Rare copper and lead hydroxyl chlorides such as boleite, cumengite, and pseudoboleite claim the Boleo district for their type locality. Gypsum crystals up to a meter and more are reported from several washes north of Santa Rosalia, and just off the coast southeast of Santa Rosalia in the Sea of Cortez is Isla San Marcos, a well-known and still-operating gypsum mine. Sulfur is associated with the geothermal area on the flanks of the Tres Virgins. Other minerals noted from Baja Sur are boulangerite, black tourmaline, and sulfur from localities south of La Paz.
Table 1 - Abbreviated list of minerals from the Boleo district 

Table 2 - Abbreviated list of minerals from the Baja California Norte 

Table 3 - Abbreviated list of minerals from Baja California Sur outside of the Boleo district 

Table 4 - Abbreviated list of other minerals from the Baja Peninsula 

Selected bibliography

Books
Gastil, R. G., Phillips, R. P., and Allison, E. C., 1975, Reconnaissance geology of the State of Baja California: Geological Society of America, Memoir 140,70 pp.
Panczer, W. D., 1987, Minerals of Mexico: Van Nostrand Reinhold, New York, 459 pp.

Articles
Bariand, P., Boulliard, J. C., Chancelier–Dumielle, I., and Tournis, V., 1998, Famous mineral localities: Boleo, Baja California, Mexico: The Mineralogical Record, Mexico, Special Issue I.
Barton, M. D., Staude, J–M. G., Zurcher, L., and Megaw, P. K. M., 1995, Porphyry copper and other intrusive-related mineralization in Mexico; in Porphyry copper deposits of the American Cordillera: Arizona Geological Society, Digest, v. 20.
Coolbaugh, D. F., Hernandez, A. 0., Perez, A. E., and Muller, R. M., 1995, El Arco porphyry copper deposit, Baja California, Mexico; in Porphyry copper deposits of the American Cordillera: Arizona Geological Society, Digest, v. 20.
Salas, G. P., 1991, Baja California Peninsula metallogenic provinces; in Salas, G. P. (ed.), Economic geology, Mexico: Geological Society of America, Centennial Special Volume, The Geology of North America, v. P-3, pp.177-178.
Swoboda, E., 1998, Boleo, a classic locality reworked: The Mineralogical Record, Mexico, Special Issue I.
Wilson, I. F., and Rocha, V. S., 1991, Geology and mineral deposits of the El Boleo copper mine, Santa Rosalia district, Baja California Sur; in Salas, G. P. (ed.), Economic geology, Mexico: Geological Society of America, Centennial Special Volume, The Geology of North America, v. P-3, pp. 195-196.

Maps
Automobile Club of southern California, 1996, Baja California.
Gastil, R.G., Phillips, R. P., and Allison, E. C., 1971, Reconnaissance geology map of the State of Baja California. Knight, E.E., and Arey, L. M., 1930, Map of lower California and the northwestern states of Mexico.
Ramos, E. L., 1976, Carta geologica de la Republica Mexicana.
Other
Domitrovic, A. M., 1998, Combined botany/geology research reconnaissance trip to Baja: unpublished road log, Arizona–Sonora Desert Museum.
Minch, J. A., and Leslie, T. A., 1979, Geology road log, La Paz to Tijuana: Geological Society of America.