Abstract
Geothermal systems can provide significant amounts of hydrothermal sulfur to surface waters, increasing salinity and avoiding some of the common anthropic uses. The objective of this study was to investigate the sedimentary neoformation of S-bearing phases in organic matter-rich sediments from a saline lake with hydrothermal inputs (Sochagota Lake, Colombia). Detrital kaolinite and quartz are the main minerals of the materials deposited in the Sochagota Lake. Neoformed clay minerals (illite and illite-dioctahedral vermiculite mixed layers) are concentrated in the central and northern part of the lake in sediments with high organic matter content. The most organic matter-rich materials are characterized by S-bearing minerals: mackinawite, pyrite, and elemental sulfur (S°). FESEM, high-resolution transmission electron microscopy (HRTEM), EDS, and Raman microspectrometry have revealed the presence of cell-shape aggregates of mackinawite nanoparticles filling the inner part of plant fragments, indicating that microorganisms were involved in the hydrothermal sulfur uptake. The alteration of mackinawite in free sulfide excess environment produced the formation of framboidal pyrite. The evolution to conditions with the presence of oxygen favored the formation of complex S° morphologies.
Highlights
The presence of sulfur as an important component is widely extended in many hydrothermal systems controlling the geochemistry and distribution of most of the trace elements in geothermal systems [1,2]
This study aims to investigate the sedimentary neoformation of S-bearing phases in organic techniques, as fieldfrom emission scanning microscopy (FESEM), high-resolution transmission matter-rich such sediments a saline lake electron with hydrothermal inputs
The results of this study revealed that the materials formed at the Sochagota Lake exhibited significant differences in the grain size, mineral assemblage, and organic matter content according to the distance from the entrance of the hydrothermal inputs (El Salitre)
Summary
The presence of sulfur as an important component is widely extended in many hydrothermal systems controlling the geochemistry and distribution of most of the trace elements in geothermal systems [1,2]. The presence of alkaline hot springs is very frequently found as surface waters, representing the composition of the geothermal reservoir [3]. The boiling of the reservoir can produce fluids enriched in volatile gases such as CO2 and H2 S, which proportion can change depending on the degree of boiling (H2 S content increases with increasing of boiling). H2 S hydrothermal fluids mix with non-thermal surface waters producing SO4 2− -rich waters due to the oxidation of the hydrothermal H2 S [1,4]. Spring discharges of SO4 2− -rich fluids may alter the surface waters, producing important environmental effects in downstream waters, e.g., increasing salinity and avoiding some of the anthropic uses of the waters. Strong eutrophication [5,6] favors the deposit of organic matter-rich materials where the Minerals 2020, 10, 525; doi:10.3390/min10060525 www.mdpi.com/journal/minerals
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