EXPLORING MINERALOGICAL AND MICROBIOLOGICAL EVIDENCE FOR A HYPOGENIC ORIGIN OF LEHMAN CAVES, GREAT BASIN NATIONAL PARK

Lehman Caves is set in mylonitic marble in the Southern Snake Range of eastern Nevada, USA, and is part of Great Basin National Park. It is the longest cave in Nevada, and consists of a single cavern with several branching passages, one known as the Gypsum Annex. Recent morphological evidence described by Hose et al.¹ indicate abundant features within the Gypsum Annex consistent with a hypogenic, sulfuric acid speleogenetic origin, in contrast to earlier and limited descriptions of the cave. They propose a two-stage speleogenetic model, with initial sulfuric acid speleogenesis as the main dissolution event, followed by a later stage of meteoric water overprinting most of the cave.

Here we examined deposits throughout both the Gypsum Annex and the rest of the cave to evaluate the origin of gypsum and other sediments within. We used microbiological analyses to probe the geomicrobiological processes that might be present in the modern cave. Microbial biomass in most of the sediments is very low, although preliminary data suggest segregation of microbial species within different passages of the cave, and a potential use of N as an energy source for growth. Bulk mineralogical composition was determined with powdered X-ray Diffraction (pXRD), and for select samples, scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) were used for further visualization and quantitative elemental analysis. White floor and wall deposits in the Gypsum Annex contained appreciable levels of gypsum in several locations. Two floor deposits in the Gypsum Annex were observed during sampling to contain some very small deposits of a yellow mineral which indicated under SEM a platey structure consistent with descriptions of a uranyl-vanadate mineral known as metatyuyamunite. Metatyuyamunite has been described in several other hypogene SAS caves and is theorized to be related to the migration of hydrothermal waters during speleogenesis. Petrographic analysis of thin sections, currently in progress, will be used to evaluate diagenetic processes in the white deposits and look for potential traces of past life.

1. Hose LD, Duchene HR, Jones DS, Baker G, Havlena ZE, Sweetkind D, Powell JD (in review) Hypogenic karst of the Great Basin. (Fieldtrip Guidebook for the 2021 Cordilleran Section of GSA, submitted to GSA Field Guides).