New Mexico Geological Society Annual Spring Meeting — Abstracts

We are resampling geologic material, including stream sediments, mineralized rocks, mine wastes, and host rocks, in the Zuni Mountains, west of Grants in Cibola and McKinley Counties as part of a project with the U.S. Geological Survey’s Earth MRI program. The purpose of this sampling is to assess the critical minerals potential of this area, as well as to train the next generation of geologists and engineers in modern exploration techniques.

Critical minerals are mineral commodities that are essential to the economic and national security of the U.S., and are from a supply chain that is vulnerable to global and national disruption. In the mining industry, minerals refer to any rock, mineral, or other naturally occurring material of economic value, including metals, industrial minerals, energy minerals, gemstones, aggregates, and synthetic materials sold as commodities, including critical minerals. In many cases, mineral deposits are available in the world for specific critical minerals, but the real challenge for the U.S. economy and security is potential supply disruptions of these essential commodities.

Re-examination of the Zuni Mountains for critical minerals is important because of the diverse geology in the area as well as the need for critical minerals in the U.S. Most of the exposed rocks in the Zuni Mountains consist of Proterozoic granites, pegmatites, and metavolcanic rocks. Permian sedimentary rocks consist primarily of the Abo Formation, Yeso Group, Glorieta Sandstone, and San Andres Formation. Quaternary basalt flows and cinders are found throughout the southern portion of the area. The major types of mineral deposits in the Zuni Mountains include 1) veins and replacements in Proterozoic rocks, 2) stratabound, sedimentary-copper deposits, 3) fluorite veins, 4) episyenites (REE-Th-U metasomatic bodies), 5) high-calcium limestone, 6) volcanic cinders (scoria), and 7) iron deposits. Potential deposits are cobalt-nickel-platinum group metals in ultramafic rocks and pegmatites. Base and precious metals were found in the Zuni Mountains mining district circa 1900 and at least one metal mill was built in the district. Total reported production from the district amounts to more than 30,000 lbs copper, 260 oz silver, and 2 oz gold from 1923 to 1965; additional copper, gold, and silver production probably occurred during the late 1800s.

In order to train the next generation of geologists and engineers, a graduate-level exploration geochemistry class was taught by the lead author during the fall semester of 2023. Sampling in the Zuni Mountains was conducted primarily by class members, which allowed 17 students with varying field experience to learn how to plan and execute a geochemical sampling program. The students were split into five groups to sample different areas within the Zuni Mountains. Approximately 90 samples have been collected in the Zuni Mountains. Unfortunately, the chemical analyses were not received in time for the class to interpret the data before the end of the semester, but a graduate student and some of the students will continue with the project.

The class learned valuable lessons in team work, field safety and the importance of good communication during this project. Some groups experienced muddy roads, even getting a truck stuck on one occasion. Satellite communicators were used to inform the instructor of the situation and retrieve everyone, including the truck, safely.

Preliminary results indicate that some areas near the stratabound, sedimentary-copper deposits have elevated heavy rare earth elements (REE), vanadium, cobalt, and arsenic. The northern Zuni Mountains also appear to have elevated REE, probably associated with the granitic rocks and pegmatties. Quartz Hill and Copper Hill areas in central Zuni Mountains have elevated arsenic anomalies surrounding those areas of known Cu-Ag veins and stratabound, sedimentary-copper deposits. Additional sampling in the Zuni Mountains is warranted as geochemical data are analyzed. Petrographic investigations also will be conducted on thin sections prepared from hand samples collected in the district using optical microscopy and electron microprobe analytical methods.