Hydraulic and Physical properties of modern sinter deposits: El Tatio, Atacama

Abstract:

Sinters are sedimentary, siliceous deposits, and are common in geothermal areas. Formation occurs in two steps. Hot water circulates underground, and dissolves silica from the host rock. Silica then precipitates at the surface as water is discharged from hot springs. Extensive sinter formations are linked to up-flow areas of fluids originated in high temperature (>175 °C) reservoirs. Sinter samples provide a guide for geothermal and epithermal ore deposit exploration. Fluid geochemistry, microbial communities, and environmental conditions of deposition determine the texture of sinter. To better understand the water balance in geothermal systems, and interpret geophysical observations, we studied 21 samples of modern geyserite sinter deposits (<10,000 years) from an active geothermal field located in the north of Chile, El Tatio. We measured the physical properties (hydraulic, seismic, and electrical), and internal micro-structure (using X-Ray micro- tomography). The pore structure, and thus hydraulic and physical properties, are controlled by the distribution of microbial matter. Based on velocity-porosity relationships, permeability-porosity scaling, and image analysis of the 3D pore structure, we find that the sinter more closely resembles vesicular volcanic rocks than clastic sedimentary rocks.