New Mexico Geological Society Annual Spring Meeting — Abstracts

New Mexico lies at the eastern edge of a well-known metal-bearing province, hosting numerous Laramide and Paleogene mineral deposits. Southwestern New Mexico contains two spatially overlapping mineralization events: the Laramide porphyry copper (±Mo, Au) and Paleogene Mo-W deposits. However, little work has been done to properly characterize and decipher the differences in these mineralization events. Further study is
required better to understand their timing, size, and mineral potential.

Recent work has placed these deposits into three mineral-producing pulses:
~78-71 Ma Laramide pulse 1; Piños Altos, 78.55±1.75 Ma, Copper Flat, Hillsboro district, 75.9±0.66 Ma, and Oro, Eureka district 71.4±0.19 Ma.

~59-50 Ma Laramide pulse 2; Lordsburg, 59.25-57 Ma, Santa Rita, 59.05±0.36 Ma, Hanover-Hermosa Mountain, Fierro-Hanover district, 58.3±0.7 Ma, McGhee Peak, Peloncillo Mountains, 57.28±0.65 Ma, Tyrone, 55.2±0.6 Ma, Lone Mountain, 50.6±1.9 Ma.

~40-30 Ma Paleogene pulse; Mo-W deposits. The Camel Mountain, Eagle’s Nest, and Tres Hermanas districts.

Cu-porphyry deposits are generally large, low-grade deposits containing Cu, Fe, Mo, and Au sulfides (and other metal sulfides). They are associated with porphyritic intrusions exhibiting characteristic alteration styles such as propylitic, phyllic, and potassic. These porphyry deposits can also be spatially and temporally associated with skarn, carbonate replacement, and polymetallic vein deposits. Laramide deposits, especially porphyry Cu deposits, are often large-scale, low-grade deposits. Paleogene Mo-W deposit scale and grades have not yet been thoroughly evaluated, and there is potential for porphyry Mo-W and periphery skarn deposits during the younger extensional period. This is especially exciting given the unique suite of critical commodities in the MoW deposits compared to the Laramide porphyry copper deposits. Alas, these deposits all have the potential to host various critical minerals, including Cu, Zn, Bi, Co, Ni, rare earth elements (REE), Te, and W, along with hosting significant gold, molybdenum, and other commodities according to their unique geochemistry and genesis of mineralization. Critical minerals may be found as substitutions within diffuse gangue minerals or concentrated as mineralized veins. Hence, their mineralization versatility is essential for the future economy of the United States.

New whole-rock geochemical data have highlighted areas within Southwestern New Mexico where the critical minerals potential requires further study. Geochemical studies have shown Laramide porphyry copper deposits to have higher anomalous copper concentrations above the average composition of the upper continental crust. For example, Piños Altos, a Laramide copper porphyry deposit, has moderate copper potential and high Pb-Zn potential, with values of Zn >1%, Bi >1000 ppm, Co to ~1000 ppm, and Te to 13 ppm in the drill core. Tungsten concentrations within Paleogene Mo-W deposits are more elevated compared to the Laramide porphyry copper deposits. Districts like Tres Hermanas, a suggested Paleogene Mo-W deposit, have tungsten concentrations up to 10,000 ppm hosted in minerals like scheelite.

Although previous studies have started to characterize and decipher the differences in these mineralization events, further study is required to understand better their timing, size, and mineral potential, especially for the younger Paleogene Mo-W deposits. Previous dating attempts of these intrusions have produced conflicting ages. Imprecise K-Ar age determination appears to be much older than expected. For example, the current geochronology from the 40Ar/39Ar dating method suggests both Laramide and Paleogene magmatism in the McGhee Peak, Eureka, and Sylvanite districts. New geochronology is ongoing, dating the host plutons and their mineralization pulses. This research aims to further characterize the timing and mineral potential of these mineral-producing pulses. New emplacement ages of the host plutons will create a more coherent history of magmatism and mineralization in Southwestern New Mexico.