New Mexico Geological Society Annual Spring Meeting — Abstracts

Karst terrains contain many types of mineral deposits by providing ideal deposition cavities for minerals. Minerals associated with karst have been exploited for many years. More than 80 mining districts in New Mexico are in carbonate rocks and most have some indication of karst prior to, during, or after mineral deposition. Many of these deposits could not have formed without some karstification. Mineralization and alteration are strongly controlled by secondary porosity such as faults, fractures, brecciation, and dissolution features produced as a result of karstification. Lead-zinc deposits hosted by carbonate rocks in New Mexico account for 37% of the lead and 56% of the zinc production from the state. Mines from the Todilto Limestone in the Grants district account of 2% of the total uranium production. Uraniferous collapse-breccia pipes in the Cliffside, Doris, and Jackpile-Paguate mines have yielded uranium ore as part of mining adjacent sandstone deposits. More than 600 collapse-breccia pipes are found in the Ambrosia and Laguna subdistricts, but only a few are uranium bearing. The pipes were probably formed by solution collapse of underlying limestone or evaporate.

Furthermore, the sedimentary rocks subjected to karst are potential commodities. New Mexico is knwon for large reserves of limesone, gypsum, potash, and halite. The Carlsbad potash district is the largest potash producing area in the U.S. New Mexico ranked 7% in gypsum production in the U. S. in 2001. Limestone is quarried throughout New Mexico for aggregate, cement, concrete, crushed stone, dimension stone, and specialty uses. More than 70% of crushed stone produced in the U. S. is from carbonate rocks. Guano (a source of nitrate) also was mined from caves throughout New Mexico in the late 1800a and early 1900s.

Geologic hazards related to mining of mineral deposits in karst terrains include removal of rock that results in subsidence (i.e. formation of induced sinkholes, caves), lowering of the ground water (locally resulting in subsidence), contamination of ground water (i.e. waste water discharge, acid mine drainage), and changing ground-water flow patterns (including increased mine water drainage). However, the effects of mining in karst in New Mexico are poorly documented. Future production of these resources can be accomplished with no significant impacts to the environment, if done carefully with a complete understanding of the geology.