APPLYING U-TH DISEQUILIBRIUM FOR DATING SILICEOUS SINTERS

Hydrothermal systems are vital to the crustal transport of heat used for geothermal energy and thus, understanding their long-term evolution is important for resource characterization. Meteoric water is an important source of hydrothermal fluid, therefore, climate acts as one of the primary controls on the evolution of these systems. Although modern systems have been dated to the Pleistocene/Holocene using ¹⁴C dating, bacterial mats present in hydrothermal deposits can contribute old carbon, generating a reservoir effect. High temperature (>170℃) hydrothermal systems are commonly marked by deposits of micro-laminated siliceous sinter, which have the potential to provide independent means for dating hydrothermal histories via the U-Th disequilibrium method. While U-Th dating was utilized in previous studies, it was not applied systematically. A refined dating methodology of sinters could offer more reliable ages, and potentially provide insights into the climatic impacts on groundwater and geothermal circulation. For this project, we perform U-Th dating via TIMS analysis on samples collected from El Tatio Geyser Field in the altiplano of northern Chile. TIMS provides a detailed chronology and requires less material than ¹⁴C, meaning finer layers can be sampled. By comparing existing ¹⁴C ages with U-Th results, El Tatio serves as an independent constraint for testing this methodology, with certain sampling characteristics, such as high fluorescence and low porosity, providing promising initial results. This preliminary data includes U-Th ages consistently trending younger than our ¹⁴C ages, possibly supporting the presence of an old carbon influence. Distal facies containing the highest U content show the least effect from detrital Th, but often show open-system behavior. Near-vent facies tend to date most consistently, with repeat age results on one sample even producing a statistically significant isochron.