Geology and mineral resources of the Cornudas Mountains, New Mexico

Abstract

At the request of the BLM, over 100 square miles (260 square kilometers) in the Comudas Mountains of southern Otero County, New Mexico, were evaluated for their potential for undiscovered mineral resources. There are three BLM-designated study areas in the Cornudas Mountains: Alamo Mountain, Wind Mountain, and Comudas Mountain Areas of Critical Environmental Concern (ACEC). All three ACECs include scenic peaks comprised mainly of Tertiary alkaline igneous rocks that rise above the surrounding gently rolling topography. This report incorporates geological, geochemical, and geophysical data collected in 1996 by the authors as well as compilation of existing data. The Comudas Mountains are at the eastern edge of the Basin and Range Province and within the Tertiary Trans-Pecos magmatic belt. The area is underlain by easily eroded Permian carbonate rocks and Cretaceous clastic rocks that are intruded by more resistant alkaline plugs and sills. Permian rocks exposed are, from oldest to youngest, the Hueco, Yeso, and San Andres Formations. Outcrops of Lower Cretaceous rocks are restricted to areas near intrusions, and much of the exposed Cretaceous occurs as blocks in landslide deposits along the edges of intrusions. Intrusion of the plugs and sills caused folding and warping of the Paleozoic and Cretaceous rocks; fold axes are predominantly east-trending. Surface folding, as well as geophysical data, indicate unexposed intrusive rock underlying the Comudas Mountains. The Comudas Mountains have been explored for nepheline syenite for industrial use and a resource is identified at Wind Mountain for industrial grade glass. No other exposed intrusion has potential for industrial grade glass. The area has been explored for metallic deposits associated with alkaline igneous rocks-uranium, beryllium, rare-earth elements, niobium, and gold and silver but has low potential for these deposit types. The geochemical environmental consequences of future mining would have minimal impact on the water chemistry of subsurface waters. Nepheline syenite in the Comudas Mountains, if mined, has a limited buffering capacity and contains little or no pyrite or other sulfide minerals that generate acid and degrade the water. Previous Investigations U.S. Bureau of Mines (USBM) geologists, at the request of the BLM, independently conducted an examination of identifiable mineral occurrences in the Wind and Alamo Mountains ACECs in 1992 and 1993 (Korzeb and Kness, 1994) and in the Chess Draw area northwest of Wind Mountain in 1992 (Schreiner, 1994). The only potential mineral resource identified in these evaluations was industrial grade nepheline syenite that underlies Wind Mountain. Previous investigations by the U.S. Geological Survey in this area are restricted to reconnaissance mapping by G.O. Bachman and associates during the compilation of the Geologic Map of New Mexico (Dane and Bachman, 1965).

Geology and Mineral Deposits of the Cornudas Mountains, Otero County, New Mexico

“…A number of types of potential economic commodities, including REE, have been examined in the Cornudas Mountains in Trans-Pecos area, southern New Mexico and Texas. Of most interest to this study are potential economic deposits of REE, Zr, Nb, and Be (Schreiner, 1994;Nutt et al, 1997;McLemore, 2018). REE, Zr, Nb, and Be minerals are found in phonolite dikes, skarns, and the lower unit (PEnsp2) of the Wind Mountain nepheline syenite laccolith.…”

“…Other dikes, sills, and plugs are buried by sedimentary cover as indicated by subsurface drilling (King and Harder, 1985;Scaar, 1986), geophysical surveys (Bultman, 2021(Bultman, , 2022, and suggested by structural anomalies (i.e. folds, synclines, faults; U.S. Borax, 1986;Nutt et al, 1997;O'Neill and Nutt, 1998) in the overlying sedimentary rocks.…”

Rare Earth Elements (REE) Deposits Associated with Great Plain Margin Deposits (Alkaline-Related), Southwestern United States and Eastern Mexico

“…Detailed geologic mapping of several districts in the GPM portion of the North American Cordilleran alkaline-igneous belt have documented evidence of local structural control of intrusive rocks and mineral deposits [78][79][80]87,108,122,170]. REE deposits are typically found along local faults (Figures 3, 7 and 9).…”

“…Other analyses [168] also are low and subeconomic: as much as 3790 ppm total REE, 2332 ppm Nb, 92 ppm Be, and 3137 ppm F. Reconnaissance mapping of the area reveals no additional deposits and the limited geophysical surveys are inconclusive [170], but detailed mapping of the areas surrounding Wind Mountain is required to properly assess the economic potential. Still, additional mineral-resource potential in the Cornudas Mountains is probably limited [168,170], but detailed geochemical, geophysical, and other exploration techniques are required to properly evaluate this area, especially in dikes and along intrusive contacts with the limestones. In the Chess Draw area (northwest of Wind Mountain), a few radioactive dikes and Th-REE-fluorite (±U, Nb) epithermal veins and breccias have been examined for mineral-resource potential.…”

“…The host igneous rocks exhibit typical light REE-enriched chondrite-normalized REE patterns of alkaline-igneous rocks with no europium anomaly (Figure 17c). The Cornudas Mountains have been examined for potential deposits of Th-REE-fluorite (±U, Nb) epithermal veins and breccias (with associated REE, Au, Ag) and nepheline syenite as specialty, dimension and crushed stone [167][168][169][170]; but there has been no production except for test shipments of nepheline syenite for use as sand-blasting material in 1995. Table 3 for a summary of their lithology and age.…”