Manifestations of sulfuric acid speleogenesis in the Mulapampa travertine, Central Andes of Peru: evidence from the Gruta con Lago

Sulfuric acid speleogenesis (SAS) is a form of hypogene speleogenesis characterized by the formation of caves in carbonate rocks due to the presence of sulfuric acid. This study focuses on the Gruta con Lago, one of three caves identified in the Mulapampa travertine, located in the central Andes of Peru. These caves are accessed through collapse sinkholes, and much of their morphology results from roof breakdown. The bottom of the studied cave is situated at the current water table. Despite the absence of typical solutional features associated with SAS caves, mineralogical and geochemical evidence of speleogenesis involving H2SO4 has been found in Gruta con Lago. Significant accumulations of gypsum deposits on the cave floor and replacement gypsum crusts on walls – both considered by-products of SAS – are present. Cave gypsum samples exhibit negative sulfur isotopic composition (ranging from -19.4 to -8.2‰) and oxygen (ranging from -9.0 to -1.3‰), which are indicative of sulfide (H2S) oxidation. This article discusses potential scenarios of SAS events in the evolution of hypogene karst in the Mulapampa travertine. It also considers the significance of the proximity of the active volcanoes of the Ampato-Sabancaya Volcanic Complex (ASVC) and seismogenic crustal faults in the formation of a thick travertine cover and the potential for SAS processes.