New Mexico Geological Society Annual Spring Meeting — Abstracts

Exploration geochemistry is important for locating critical minerals resources that are crucial to meeting the demand placed by a variety of industries, and stream sediment sampling is often the first step towards achieving this goal. This exploration technique has been shown to be a reliable way of locating deposits in the early stages of exploration over large areas. In the past, the Zuni Mountains have been mined for their deposits of copper, fluorite, and barite, although obsidian, turquoise, azurite, malachite, and copper have been (and continue to be) mined by the Zuni people and later prospectors. The Zuni Mountains are a small mountain range located in northwest New Mexico, near Grants. These mountains were formed during the Laramide orogeny and lie along the Jemez Lineament. While much of the lithology of the Zuni Mountains is sedimentary, there are units of Precambrian basement rock, some of which have been metamorphosed. With the demand for critical minerals increasing, the NMBGMR has been contracted by the USGS to evaluate the critical minerals potential of the Zuni Mountains through stream sediment sampling and chip sampling. From the data that were received from USGS (all stream sediment and chip sample data from the August 2023 field trips), there are some key differences between the initial NURE (National Uranium Resource Evaluation) data and the Zuni Mountains project data.

Though the Zuni Mountains project is mainly focused on sampling new locations and evaluating the critical minerals potential of the district, there are some key details that are different between the original NURE data taken in 1970s and the newly generated data. The first key difference between the two projects is the mesh size of stream sediment samples. The original NURE sampling project used a 150-micron mesh, while this project used a 2 mm mesh to sample stream sediments. This creates differences in the data due to the properties of different critical minerals. For example, the original NURE data had higher concentrations of vanadium when compared to Fe₂O₃ than the new data collected in late 2023. This is due to vanadium having the tendency to be absorbed into clay structures or iron oxide coatings, and the original NURE sampling procedures collected clay-sized stream sediments. Another key difference is what elements the two projects analyzed. The original NURE program did not analyze for elements such as Cd, Cs, Rb, Sb, and Y, all current critical minerals. This is possibly due to what the laboratory could analyze for at that time. Given the two key differences, the current data can now be evaluated based on what was not evaluated in the previous NURE data. New geochemical data may help gain a better understanding of critical minerals behavior in coarser size fractions. When looking at the current data from the Zuni Mountains district on a chondrite normalized graph (McDonough and Sun, 1995), both show an enrichment in REEs, and the datasets correlate similarly even though some REEs weren’t analyzed for in the NURE data. Anomalies of REEs are above 150 ppm and are found within the granitic gneisses, the Paleoproterozoic rhyolite and felsic volcanic units, along faults in the southeast portion of the district, and few along the shear zone. Anomalies of Cu (>22 ppm) were found along the shear zone and in the granitic gneisses and red sandstones. Sb anomalies (>3.8 ppm) were found mainly along a fault in the northwest part of the district and only two were located in the granitic gneiss unit. Ba (>850 ppm) anomalies were found along faults, the shear zone, granitic gneisses, and the Paleoproterozoic rhyolite and felsic volcanic units. Zn anomalies (>16 ppm) were found in the Paleoproterozoic rhyolite and felsic volcanic units, granitic gneisses, along the shear zone, with some found along the faults in the southeast area of the district.