Bulletin 21—Fluorspar Resources of New Mexico

By H. E. Rothrock, C. H. Johnson, and A. D. Hahn, 1946, 239 pp., 15 figs., 23 plates. Supersedes Bulletin 4.

This bulletin consists of three parts; Part I: Geology and Description of the Deposits; Part II: Mining and Milling of Fluorspar in NM; and Part III: Uses and Marketing of Fluorspar. The investigation of fluorspar deposits in NM by the USGS was undertaken to stimulate output of fluorspar for war uses, to determine the available reserves, and to supply geological information to war agencies and operators. Many of the data obtained for these purposes are confidential, but those that are not have been assembled in this report to show the progress of investigation and to indicate the work that remains to be done.

In the attempt to encourage new development, priority was given to newly discovered or unproved deposits; thus some of the larger operating properties were not completely investigated. Descriptions of some of these larger properties, therefore, are less detailed than their importance as sources of fluorspar justifies. Some areas, such as the Ladron, San Andres, and Oscura Mountains, were not studied during the present survey, and so little has been written about them that they are not reviewed.

Most of the information in this report was gathered between October 1942 and December 1944. The urgent need for information regarding fluorspar resources, the large number of deposits to be investigated in a short time, and shortages of personnel made it necessary to confine the greater part of the work to studies of small areas along veins and to the preparation of vein and mine maps. For short periods, as many as three field parties employing eight geologists were simultaneously engaged in the work, but usually there were no more than three geologists working on the project.

All the known fluorspar deposits in NM are in mountainous regions. The southwestern region, which is the oldest and the most consistently productive, includes Grant, Lune, Catron, and Hidalgo Counties. It is characterized by intense volcanism of Cretaceous and Tertiary ages. Most of the fluorspar deposits lie within an elliptical area 70 mi long and 55 mi wide, with the Burro Mountains uplift at its center. The northwestern region includes the deposits within the core of the Zuni Mountains, Valencia County. In recent years this region has become one of the most important sources of fluorspar in the state. The south-central region includes Doña Ana, Otero, Sierra, Socorro, Lincoln, and Bernalillo Counties, in the southern part of the Rio Grande valley. It is characterized by a belt of north-trending valleys between block-faulted mountains, and contains two large intrusive masses- the Gallinas Mountains laccolith in Lincoln County and the Organ Mountains batholith in Doña Ana County. The fluorspar deposits in this region are in sedimentary rocks or in igneous rocks close to their contacts with sedimentary rocks. In the early days of fluorspar mining this region was very important; the fact that little fluorspar came from it during the period 1942–1944 is not a measure of its potentialities.