Sinter deposits
Sinters are sedimentary, siliceous deposits commonly found in geothermal areas. The formation occurs in two steps: hot water circulates underground, and dissolves silica from the host rock; then, silica 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. They provide a guide for geothermal and epithermal ore deposit exploration. Fluid geochemistry, microbial communities, and environmental conditions of deposition determine the texture of sinter.
Radiocarbon dating of sinter deposits
Mid-to-low temperature sinter facies host and preserve a large diversity of organisms, including remains of plants and animals, providing an opportunity for collecting organic matter for radiocarbon dating.
SEM images of organic material in sinter (a) grass fiber, (b,c) pollen grains, (d) bacterial filament, (e) diatom, (f) grass cross section
I found that bacteria can contaminate radiocarbon measurements leading to old radiocarbon ages. The stable carbon isotope 13C of the dated carbon helps us to infer if the dated organic matter is contaminated or not, and thus provides reliable ages. Reliable ages are usually associated to near vent and distal deposits.
Physical properties and porosity of sinter rocks
Fluid geochemistry, microbial communities, and environmental conditions of deposition determine the texture of sinter and pore framework. Porosity strongly influences physical and hydraulic properties of rocks.
Individual pores resemble spherical to elongated bubbles, consistent with effective medium models for the measured seismic velocity of opal containing moderate aspect ratio penny-shaped cracks. Porosity and permeability in sinter are different than clastic sedimentary rocks, and more similar to vesicular volcanic rocks (e.g., pumice). However, permeability shows a directional dependence with higher values in the direction parallel to the layering than in the orthogonal direction, similar to other layered sedimentary rocks.
(a, b) Micro X-ray tomography of a sinter rock and it pore structure, and (b,c) statistics of pores volumen
Microscopic distribution and pore structure in sinter rocks