SINTER DEPOSITS RECORDING THE EVOLUTION OF HYDROTHERMAL SYSTEMS (Invited Presentation)

Siliceous sinter are sedimentary deposits that form as subterranean hot fluids dissolve silica from the surrounding rock at temperatures >170^oC. Silica precipitates at the surface around boiling hot springs and geysers as water cools down and evaporates. Sinter deposits can guide geothermal and mining exploration. Additionally, sinter can help us understand early life on Earth and other planets since they can preserve information about bacterial communities and their ecosystems. To improve the interpretation of sinter deposits, and understand the evolution of hydrothermal systems, we need to establish accurate chronologies and differentiate the role of biota, environmental conditions, and hydrodynamics. El Tatio, in the Chilean Altiplano, is an excellent natural laboratory to understand the formation of silicious sinters. The preservation of original chemical and textural patterns is exceptional due to the arid conditions of the Atacama Desert. According to two independent dating techniques, ¹⁴C and U-Th, El Tatio has been actively depositing sinter since the Late Pleistocene/Holocene. However, not all sinter facies are suitable for dating. The extension and distribution of ages indicate vigorous activity in the past that has been waning over time. Although there are no recent volcanic eruptions in the area, a large body of cooling magma is necessary to sustain this long-lived hydrothermal system. In situ experiments of silica precipitation indicate that cooling patterns and biota affect the precipitations rates of silica. The fractionation of trace elements depends on distance from the vent. The content of trace elements in sinter suggests that significant amounts of metals have been discharged by El Tatio waters since the onset of hydrothermal activity. These results highlight the important role of hydrothermal systems in transporting heat and metals toward the surface. Sinter deposits provide important records that can be used to understand the evolution of hydrothermal.