The geochemistry of El Misti volcano,Peru fumaroles

El Misti is a 5822 m strato volcano in southern Peru. The mineralogy of the fumaroles is essentially sulfur, anhydrite, gypsum and ralstonite which are precipitated by acid vapors at 100°C–125°C. There are 2 to 6 parts per thousand chloride concentrations and several parts per million sodium, potassium, magnesium, calcium, iron and zinc concentrations in the condensed vapors. Elemental ratios indicate near complete leaching of the wall rock by the vapors. Arsenic and selenium are contaminants of the sulfur but are absent from the other minerals. Both the gypsum and anhydrite contain strontium and lead and show no tendency to fractionate these metals. The anhydrite alone contains significant thallium and bismuth. Bromine, strontium, thallium and lead are present in the ralstonite. The average δ D and δ O¹⁸ ratios from the fumarolic condensates are ?31.4 ‰ and +4.8 ‰ respectively. A marine contaminated heavy water source at depth is indicated as the parent water for the vapors.