| The clay minerals occurring in caves of the Guadalupe Mountains of New Mexico include kaolinite, dickite, hydrated halloysite, illite, montmorillonite, trioctahedral smectite (saponite and stevensite), and palygorskite. Minerals found to be associated with these clays include aluminite, alunite, natroalunite, jarosite, calcite, dolomite, aragonite, huntite, magnesite, gibbsite, nordstrandite, goethite, gypsum, hydrobasaluminite, metatyuyamunite, tyuyamunite, quartz, todorokite, and rancieite. The clay minerals found to be authigenic in the caves are hydrated halloysite, montmorillonite, saponite, stevensite, and palygorskite. Hydrated halloysite and alunite are by-products of the sulfuric acid-related speleogenesis that formed many of the larger caves; they formed through alteration of montmorillonite and illite. Montmorillonite has formed in moistened floor and ledge sediments, but these occurrences are not common. Trioctahedral smectite precipitates in association with Mg-carbonates such as dolomite and huntite. Evolution of the formation of these silicates follows the sequence of carbonate mineral formation. Amorphous silica and poorly formed silicates precipitate with Mg-calcite and aragonite in stalagmites and crusts, and trioctahedral smectite forms with dolomite, huntite, and magnesite in moonmilks and crusts. Palygorskite forms in smectite-rich sediments such as the laminated silt and clay deposits and fracture filling sediments of Carlsbad Cavern. Dickite and illite are inherited in wall residues from the dissolution of the cave-wall bedrock by condensate or carbon dioxide of the cave air, and/or by biochemical breakdown. Dickite and illite are not cave-authigenic.; {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} dating of alunite from these caves have yielded the formation age of five caves in the Guadalupe Mountains. The ages ranged from 11.3 million years ago for Virgin Cave located at the higher elevations (2000 meters) to 3.9 million years ago for the Green Clay Room of Carlsbad Cavern at an elevation of 1090 meters. An apparent water table decline in the Capitan aquifer of approximately 1000 meters is shown to have occurred between 11 million years ago and the present. Speleogenesis, occurring along the water table, migrated from the southwest to the northeast as the water table decline and/or as the mountains were uplifted. |
