Minerals and Microbes in Lehman Caves

Written from an article by Zoë Havlena, researcher at the New Mexico Institute of Mining and Technology, for The Midden (Great Basin National Park), Vol. 24, No. 1, Summer 2024.

The Gypsum Annex of Lehman Caves, whose white walls hold clues to how the cave formed. NPS / G. Baker.

Lehman Caves, in Great Basin National Park, is famous for its shields and other spectacular speleothems. Its less showy minerals also hold clues to the cave's history. In 2018 and 2019, researchers sampled many mineral deposits in a collaboration with cave expert Dr. Louise Hose of the University of Nevada, Reno.

A cave made from below

Hose showed that many features of the cave, especially in the protected Gypsum Annex, point to a rare origin: hypogene speleogenesis. The cave was dissolved by deep groundwater rising from below, not by rain seeping down. When that water is rich in hydrogen sulfide, the process is sulfuric acid speleogenesis (SAS), which often leaves plenty of the sulfate mineral gypsum (CaSO₄·2H₂O). Hose described it in The Midden, Summer 2018.

Where did the gypsum come from?

The Gypsum Annex is named for its white minerals, but no one had measured how much was gypsum or what else was there. Was the gypsum left by the original acid phase — which Hose suggests may have been more than 10 million years ago — or laid down later?

The team used powder X-ray diffraction, electron microprobe analysis and scanning electron microscopy to identify the minerals. Many samples held gypsum, but not all. Then stable sulfur isotopes — ratios that different biological and physical processes shift in telltale ways — pointed to the sulfur's source.

The answer: the gypsum does not seem to date from the cave's earliest hypogene phase. More likely it was deposited later, during one or more periods when surface water seeped in.

A gypsum flower in the Gypsum Annex. NPS / G. Baker.

A surprise mineral: traces of metatyuyamunite, a yellow uranium–vanadium mineral crust, Ca(UO₂)₂(VO₄)₂·3–5H₂O, known from other ancient hypogene caves around the world.

Life on almost nothing

DNA sequencing reveals the microbes living in places like caves. Little is known about life on mineral surfaces in caves like Lehman, which are dry and extremely low in nutrients (oligotrophic).

• Very little life: every Gypsum Annex sample had very low biomass — even bacteria and archaea struggle to find energy there.
• Different communities: the gypsum, dark "corrosion residues" and soft "punk" rock hosted different microbes from surfaces along the tour route, perhaps because the route is nearer the entrance and more affected by people.
• Unusual residents: groups such as Nitrosococcales and Thaumarchaeota, which may live on inorganic nitrogen compounds.

Why it matters

The work adds to what is known about ancient hypogene caves and how microbes colonize cave minerals — and shows why caves like Lehman must stay protected for future discoveries. The results appear in Geobiology (2024).

Sources

Written from "Minerals and Microbes in Lehman Caves," by Zoë Havlena, published by the National Park Service in The Midden and in the public domain; rewritten in hubnx's own words. The study: Havlena, Z. E., L. D. Hose, H. R. DuChene, G. M. Baker, J. D. Powell, A. L. Labrado, B. Brunner and D. S. Jones, 2024, "Origin and modern microbial ecology of secondary mineral deposits in Lehman Caves, Great Basin National Park, NV, USA," Geobiology 22(3): e12594, doi:10.1111/gbi.12594 (preprint).