A Multi–fluid Constrain for the Forming of Potash Deposits in the Savannakhet Basin: Geochemical Evidence from Halite

Abstract

The Khorat Plateau on the Indochina Terrane is known to have formed during the closure of the Tethys Ocean, although the origin of its potash mineral deposits is a topic of current debate. Data from a borehole on Savannakhet Basin is used in this study to re‐define the evaporation processes of the study area. Geochemical analyses of halite from various borehole‐derived evaporite strata have elucidated the fluid sources from which these ores formed. Measured δ11B indicated that ore deposits formed primarily due to evaporation of seawater, although non‐marine fluids affected the later stages of the evaporation process. Fluctuations in B and Br concentrations in carnallite‐ and sylvite‐rich strata indicate the influence of fresh water. Boron concentration in carnallite unit indicated the influence of hydrothermal fluids. From the relative timings of these various fluid influxes, the evolution of these evaporates can be divided into four stages: (1) an initial marine evaporation at the beginning of the deposit's formation, where seawater (and minor fresh water) trapped on the uplifted Khorat Plateau produced sediments and salts with Br contents lower than those of normal marine‐derived evaporites; (2) a transgression stage, where seawater recharged the basin; (3) a hydrothermal infiltration stage, which was coeval with the late Yanshan movement; and (4) a stage of fresh water supply, as recorded by fluctuations in B and Br contents, inferring intermittent fresh water influx into the basin. Thus, although evaporites on the Savannakhet Basin primarily formed via marine evaporation, they were also influenced to a significant degree by the addition of non–marine fresh water and hydrothermal fluids.

Origin and evolution of intercrystalline brine in the northern Qaidam Basin based on hydrochemistry and stable isotopes

“…Natural boron exists as either tetrahedral (i.e., B (OH) 3 ) or trigonal complexes (i.e., B(OH) 4 − ) (Barth, 1993). Differences in their reduced partition function ratios and relative masses result in two stable isotopes, B 11 and B 10 , showing significant isotopic fractionation (Ren et al, 2018), leading to considerable variations in natural δ 11 B (Figure 7). Thus, boron isotopes can readily distinguish the evolution of brines.…”

Stratigraphy and geochemistry of rock salt from Maha Sarakham formation in changwat Chaiyaphum, northeastern Thailand

“…Table 1 Sequence of precipitation of evaporitic rocks ................... Taylor and McLennan (1985) Figure 7 Lithostratigraphy "A" (see figure 7) showing complete lithostratigraphic sequence discovered three salt beds Figure 10 Lithostratigraphy "B" (see figure 7) showing incomplete lithostratigraphic sequence discovered two salt beds Figure 11 Lithostratigraphy "C" (see figure 7) showing incomplete lithostratigraphic sequence discovered one salt bed Figure 16 The direction of paleoseawater from Shan Boundary ocean inflow into the Lanping-Simao basin and the Sakon Nakhon and Khorat basins respectively Swihart et al, 1986;Vengosh et al, 1992) Swihart (1996); Swihart et al (1986); Vengosh et al (1992). the δ 11 B ranges of marine evaporitic rocks compares with previous studies from the Sakon Nakhon xiv Basin (Ren et al, 2018;Tan et al, 2010;Zhang et al, 2013) and the Khorat Basin (Qin et al, 2020) The Khorat plateau of northeastern Thailand, as a part the Indochina microplate, has been formed by continuous uplift for a long period of time probably throughout the Late Cenozoic (Bunopas et al, 2001;Metcalfe, 2017;Sone & Metcalfe, 2008;Sone et al, 2012).…”

“…Geochemistry data was interpreted by bromine concentration and isotopic compositions of boron, strontium and sulphur these data are identified the marine origin (El Hite & Japakasetr, 1979;Qin et al, 2020;Ren et al, 2018;Tan et al, 2010;Zhang et al, 2013). Secondly, the non-marine origin is identified by characteristic of continental clastic unit (Utha-Aroon, 1993) and the result of Bromine concentration in halite samples (Sun et al, 2019).…”

“…Boron isotope analysis can be used to distinguished between marine and non-marine evaporate settings (Fan et al, 2015;Liu et al, 2000;Palmer & Swihart, 1996;Swihart et al, 1986;Vengosh et al, 1992). For Suvannakhet basin in Laos, extending part of the Sakon Nakhon basin from NE Thailand, Tan et al (2010) and Ren et al (2018) analyzed boron isotope in halite.…”

“…Secondly, the non-marine origin is identified by characteristic of continental clastic unit (Utha-Aroon, 1993) and the result of Bromine concentration in halite samples (Sun et al, 2019). Next, the parent rocks from hydrothermal identified by borate minerals (El Tabakh et al, 1999) and the geochemistry data of rock salt (Li et al, 2018;Ren et al, 2018). Finally, the other studies were represented the influence of mixing fluids as the consisted of different provenances fluids to forms the evaporitic rocks such as mainly marine with hydrothermal (El Timofeeff et al, 2006), mainly marine with hydrothermal and fresh water respectively (Ren et al, 2018) and hydrothermal or meteoric fluids in potash minerals of the lower salt unit (Li et al, 2020).…”