Economic geology of the Todilto Formation
William R. Berglof and Virginia T. McLemore

Abstract:

The Jurassic Todilto Formation of northern New Mexico and southern Colorado is a distinctive lithostratigraphic unit in the San Juan Basin. It consists mostly of carbonates and evaporites in a thick section otherwise dominated by siliciclastic eolianites. The Todilto has broad and diverse economic importance in New Mexico. Limestone of the lower Luciano Mesa Member is the host for important uranium deposits, mostly north and west of Grants. Uranium was also produced from the Todilto near Laguna, with extremely minor production from elsewhere in the San Juan Basin. The Todilto uranium deposits are the largest known uranium deposits in limestone in the world, and appear to refl ect a rare combination of circumstances. Intraformational folds in the Todilto, many of which localize uranium deposits, also appear to represent a somewhat unlikely combination of multiple origins; it is diffi cult to establish the relative importance of each process. Other commodities are produced from the Todilto Formation. Gypsum is produced from the upper Tonque Arroyo Member of the Todilto, which is more restricted in its occurrence than the limestone member. It has been quarried at several locations, with current production at White Mesa, near San Ysidro. At Cedar Crest, east of Albuquerque, the gypsum is suffi ciently massive to be used as a raw material for sculpture, and is known to sculptors as Cedar Crest alabaster. Another product is limestone, produced from the lower Luciano Mesa Member. Most limestone quarries are in the Todilto outcrop belt between Gallup and Grants, with intermittent current production. The Todilto is believed to be the source rock for petroleum produced from the Entrada Sandstone in the San Juan Basin. Geologic hazards associated with mining in the Todilt Formation are not well documented, but presumed minimal, with the exception of local surface land subsidence in the Ambrosia Lake area. Indoor radon associated with uranium deposits in the Todilto is a potential hazard, but most of the known deposits and mines are in sparsely populated areas.


Citation:

  1. Berglof, William R.; McLemore, Virginia T., 2003, Economic geology of the Todilto Formation, in: Geology of the Zuni Plateau, Lucas, Spencer G.; Semken, Steven C.; Berglof, William R.; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 54th Field Conference, pp. 179-189.

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