New Mexico Geological Society Annual Spring Meeting — Abstracts

Sulfuric acid karst should be considered as an integral part of the evolution of petroleum-evaporite basins. In the Delaware Basin, New Mexico and Texas, sulfuric acid karst is related to hydrocarbons, native sulfur, and Mississippi Valley-type (MVT) ore deposits through a series of sulfur redox reactions:

Stage 1 in the above redox-reaction diagram represents the microbial (Desulfo-x) production of isotopically-light H₂S from hydrocarbons in the basin. Stage 2 represents the non-microbial production of economic native sulfur deposits in the basin (e.g., Culberson sulfur mine). Stage 3 represents H₂S that migrated from basin to reef to form MVT ore deposits (metal sulfides), located in the same structural and stratigraphic traps as the caves. Stages 4 and 5 represent the migration of H₂S into the Capitan reef complex and the dissolution of cave passages by a sulfuric acid mechanism, with gypsum forming as a by-product. Thiobacillus could have been involved in the reactions of these two stages. Stage 6 represents the formation of cave sulfur from H₂S in the zone of aeration, and Stage 7 represents the oxidation of this sulfur to gypsum within the cave environment.