From abstract: Many small deposits of optical calcite (Iceland spar) were discovered in the States of Chihuahua, Durango, Sonora, and Sinaloa from early in 1942 to late in 1944. Exploration that began in Sonora led to the discovery of commercial deposits in the eastern part of that State, and subsequently other deposits were found and mined in southwestern and northeastern Chihuahua and in western and central Durango. The largest deposits can be reached by foot or by horse in from 1 to 3 hours from the nearest truck roads, but some of the small deposits are 1 to 3 days by horse from the nearest roads.

From abstract: The Talamantes district, 20 kilometers east of Parral in southern Chihuahua, has been the second largest producer of manganese ore in Mexico. Production, which started during World War I and has been more or less continuous since 1930, has totaled about 50,000 tons of ore with an average manganese content of 40 or 41 percent. The mines are on the Mesa de Talamantes, which is underlain by folded Cretaceous (?) limestone, overlain unconformably by gently dipping Tertiary rhyolite flows and tuff, volcanic breccia, agglomerate, and tuffaceous sandstone. Steeply dipping normal faults of northerly trend cut the rock and divide the mesa into a series of blocks.