DuCHENE, HARVEY R.
Cody Energy, Inc., Denver, CO
Abstract: Origin and Mineralogy of Lechuguilla Cave, Carlsbad Caverns National Park, New Mexico
Lechuguilla Cave is within the Guadalupe Mountains in Carlsbad Caverns National Park, New Mexico. The cave is 160 km long with a vertical relief of 478 m and is comprised of passages ranging from pinpoint solution cavities to large rooms and galleries. It is developed in the Permian Capitan, Yates, Seven Rivers and Queen formations.
Lechuguilla contains abundant carbonate and sulfate speleothems, as well as rare oxides and halides. Calcite is found in areas where meteoric water flows along joints and fractures. In drier areas, gypsum, aragonite, celestite, barite, alunite and native sulfur occur. Tyuyamunite, and rare fluorite are associated with drusy quartz and opal in wall crusts and coatings.
Lechuguilla is a hypogenic cave formed by acids originating in the subsurface. It was formed by the oxidization of hydrogen sulfide (HS) released from connate water at the water table. This HS was absorbed into oxygenated water on bedrock surfaces where it oxidized to sulfur and sulfuric acid. Where bedrock is limestone, sulfur reacted with calcite to form gypsum. Where bedrock is silica sandstone, no calcite was available to form gypsum and sulfur is preserved.
Hydrogen sulfide in the Delaware basin is derived from the reduction of sulfate by bacteria in the presence of hydrocarbons. Biological reduction of sulfate results in enrichment in the light isotope of sulfur. Hydrogen sulfide gas in the Delaware basin is isotopically light as are sulfate and sulfur deposits in Lechuguilla. Fluid inclusions in sulfur contain trace amounts of hydrocarbons. This suggests that acid that dissolved Lechuguilla Cave is derived from hydrocarbons in the Delaware basin.
AAPG Search and Discovery Article #90918©1999 AAPG Southwest Section Meeting, Abilene, Texas