New Mexico Geological Society Annual Spring Meeting — Abstracts

The San Juan Basin of northwest New Mexico hosts economically significant organic energy resources that have been developed and studied since the early 1900’s (Shomaker. et. al., 1971; Alamito Coal Company, 1980; Beaumont and Speer, 1981; Reddy, 1981; Hoffman, 2017), including coal from the late-Cretaceous Fruitland Formation - a sequence of mostly siliciclastic sedimentary rocks laid down along a shifting shoreline as the shallow epicontinental sea finally regressed from North America (Shomaker, et. al., 1971; Beaumont and Speer, 1981). The lithostratigraphic subunits of the Fruitland Formation exhibit significant variability in their occurrence, thickness, and arrangement. This variability is directly attributable to complex interplay between the erosive capacity of the sedimentological processes in this marginal-marine depositional system. Fruitland coals are mostly of subbituminous A rank, have low sulfur content, and are highly weatherable (Beaumont, 1981; Hoffman, 2017). These coals were laid down intermittently with a sequence of sandstones, siltstones, shales, claystones and other sediments across a spatially dynamic shoreline. The well-established geometry of the Fruitland Formation along the Chaco Slope provides a solid basis to analyze diagenetic processes (and their respective energetic capacities) controls on the occurrence and distribution of rare earth elements within the associated depositional sequences. Our primary research focus is to quantify these relationships, between the lithological, geochemical, and geophysical character of the coal-bearing Fruitland Formation and to determine the critical minerals potential.

The NM Bureau of Geology has obtained core samples from many drillholes intersecting into the Fruitland Formation in the San Juan Basin. To date, geochemical samples collected as a function of depth were taken from only one Fruitland drillhole (E-61) situated a few miles basinward to the north of the Chaco Slope where the formation is buried more deeply. Though E-61 was sampled in detail across its entire cored interval, challenges arise due to the absence of corresponding geophysical well-log data for this BLM-funded drillhole. Correlation of the lithologic units with their geochemical and geophysical properties requires new samples to be sent for geochemical analyses from drillholes with both core and the accompanying well-preserved, high-resolution wireline geophysical surveys. This poster presents detailed analysis of the Fruitland Formation’s geometry and stratigraphy using this sample selection process.

Acknowledgement: Our research benefited immensely from the stewardship of Amy Trivett and Annabelle Lopez, who manage the records and physical samples at the subsurface library. Their efforts have been crucial to our investigation, providing access to invaluable resources that continue to underpin our work.

References:

1. Alamito Coal Company, 1980, Gallo Wash Mine, Surface Mine Permit Application and Mine Plan: submitted to the Mining and Minerals Division, State of New Mexico, Santa Fe, New Mexico. *no doi*
2. Beaumont, E., and Speer, W., 1981, Coal Resources of the San Juan Basin, supplement to Chaco Energy Company's Gallo Wash Mine Surface Mine Permit Application and Mine Plan: submitted to the Mining and Minerals Division, State of New Mexico, Santa Fe, New Mexico. *no doi*
3. Hoffman, G.K., 2017, Coal Resources, in McLemore V.T., Timmons, S., and Wilks, M., eds., Energy and Mineral Resources of New Mexico: New Mexico Bureau of Geology and Mineral Resources, Memoir 50B, and New Mexico Geological Society, Special Publication 13B. 80 p. ISBN: 978-1-883905-38-5, https://doi.org/10.58799/M-50B
4. Reddy, M. R., 1981, in Carbon Coal Company: Strip Coal Resources Report of the PRLA Region, San Juan Basin KCRCA, New Mexico * no doi*
5. Shomaker, J.W.; Beaumont, E.C; and Kottlowski, F.E., 1971, Strippable Low-Sulfur Coal Resources of the San Juan Basin in New Mexico and Colorado in New Mexico Bureau of Mines & Mineral Resources Memoir 25. https://doi.org/10.58799/M-25