Exceptional variety of baryte-celestine-series speleothems in Lechuguilla Cave (New Mexico, USA)

An inventory of speleothems primarily composed of the closely related sulfate minerals baryte (BaSO4) and celestine (SrSO4) in Lechuguilla Cave (New Mexico, USA) has revealed an extraordinary variety. This includes subaerial stalactites, stalagmites, flowstone, coralloids, wall crusts, floor crystals, snow, frostwork, and subaqueous pool crystals. Large baryte and celestine crystals have also been documented in hydrothermal veins in the host rock, predating the cave and truncated when intersected by it. The respective carbonate mineral phases witherite (BaCO3) and strontianite (SrCO3), in contrast, were found to be rare in the studied speleothem samples, representing the first confirmed records from this cave. Baryte speleothems are typically composed of pure baryte, whereas celestine is usually syntactically intergrown with small baryte crystals and forms part of the most diverse assemblages of secondary cave minerals recorded in the cave to date, including species of the following mineral groups: carbonates (calcite, dolomite, aragonite, huntite, hydromagnesite, strontianite, and witherite), sulfates (gypsum), oxides and hydroxides (undetermined Mn/Fe-oxides or hydroxides), silicates (quartz, chalcedony, opal/cristobalite/tridymite, and montmorillonite), halogenides (fluorite), and vanadates (metatyuyamunite). Based on 230Th/U-series dating of directly associated carbonate minerals and gypsum, the age of formation of the various types of baryte and celestine speleothems was constrained to a range from the Middle Pleistocene to the Holocene. This confirms a formation during the ongoing post-hydrothermal and post-SAS (sulphuric acid speleogenesis) phase of epigenic normal temperature cave development. Six samples fall outside the dating range with close to secular equilibrium isotope ratios and are thus likely older than ~600 ka. While baryte stalactites, stalagmites, flowstone, and pool crystals are still forming, celestine minerogenesis, except for some of the coralloids, appears to have largely ceased in Lechuguilla Cave.