Transformation of S-Bearing Minerals in Organic Matter-Rich Sediments from a Saline Lake with Hydrothermal Inputs

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.

Low Temperature Illitization through Illite-Dioctahedral Vermiculite Mixed Layers in a Tropical Saline Lake Rich in Hydrothermal Fluids (Sochagota Lake, Colombia)

“…This evidence and our results on the distribution of illite and I-DV in the sediments of the Sochagota Lake indicate that the interaction of the hydrothermal waters of the lake, enriched in K an Fe (see [15,27,28]), and the organic matter-rich sediments promoted changes in the chemistry of clays from the sediments studied. In the central and northern parts of the lake, a significant enrichment of I-DV mixed-layer minerals and an Fe-bearing illite can be observed, which is absent in the southern sediments feeding the Sochagota Lake (and in the eastern floodplains of the Chicamocha River Basin before the Sochagota Lake).…”

“…Sedimentary rocks of Cretaceous and Paleogene ages and the outcrops of acidic vulcanites are the main geological materials in the surrounding areas of the Sochagota Lake (Figure 2) [15], which develop highly weathered soils that are rich in kaolinite and quartz, as expected for soils weathered under a subtropical highland oceanic climate. Quevedo et al [21] showed that very fine particles of I-DV minerals were formed in the materials draining the Chicamocha River Basin (which also includes the Sochagota Lake Basin) as a consequence of weathering transformations under the high humidity and moderate climate in the Tunja region of Colombia.…”

“…Quevedo et al [21] showed that very fine particles of I-DV minerals were formed in the materials draining the Chicamocha River Basin (which also includes the Sochagota Lake Basin) as a consequence of weathering transformations under the high humidity and moderate climate in the Tunja region of Colombia. These materials also feed the Sochagota Lake [15,28].…”

“…Kaolinite is the prevalent clay from the floodplains of the global Chicamocha River Basin and the Sochagota Lake Basin [25]. In fact, the Sochagota Lake drains to the Chicamocha River [15,25]. FESEM and HRTEM images as well as the sharp XRD peaks of the Sochagota Lake sediments clearly indicate that kaolinite is the main detrital mineral of the clay assemblage, especially in the zones of higher hydraulic energy, such as the southern part of the lake characterized by the presence of sediments enriched in coarse grain size fraction due to the prevalence of transport for the fine size fraction enriched in I-DV.…”

“…Deocampo [7] suggested that the interaction of clays with K-rich waters can yield sedimentary illitization. In this paper, we study the illite formation process in the Sochagota Lake (Paipa Colombia), a saline lake located in a geothermal area [15].…”