New Mexico Geological Society Annual Spring Meeting — Abstracts

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There are 24 coal fields in the San Juan Basin, northwestern New Mexico. Clinkers are found near the coal beds and are former sedimentary rocks that were baked by coal fires. When coal catches fire through various causes (wildfires, lightning strikes, spontaneous combustion through pyrite breakdown) it spreads underground and burns at high temperatures, heating up and baking the surrounding rock layers. These high temperatures cause organic materials to be removed from the sedimentary rocks that surround the coal layer. This causes the iron minerals in the sedimentary rocks to oxidize, changing the rock coloration to a deep orange-dull yellow. Clinkers can vary in durability and hardness depending on the mineral structure present in the original sedimentary rock, as well as the temperature they were exposed to during pyro-metamorphosis.

The purpose of looking at clinkers within the San Juan Basin is to examine them for critical minerals and rare earth elements as part of the DOE Core-CM project. Clinkers have not undergone drastic geochemical changes during the pyro-metamorphism process; however, some new mineral phases were formed as a result of the high temperatures. The highest detected REE concentrations are 323 ppm. However, some clinkers do contain high levels of Al₂O₃, up to 40% in some cases. While low in other critical minerals, clinkers may have potential as aluminum resources in the future.