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... These theoretical and experimental results consistently approved that during the concentration process of brine and seawater, δ 37 Cl values of brine and precipitates drop off gradually from halite to potash stage. This conclusion has been verified from δ 37 Cl values of geological samples (Xiao et al. 1994;Eggenkamp et al. 1995;Liu et al. 1995;Sun et al. 1998;Eastoe et al. 2007;Luo et al. 2012Luo et al. , 2016. Due to that the chemical compositions and precipitated mineral assemblages of brine and modern seawater are obviously different with those (enriched in Ca 2+ and depleted in Mg 2+ , SO 4 2− , MgSO 4 -poor salts) of Cretaceous seawater (Hardie 1996;Lowenstein et al. 2001;Horita et al. 2002;Demicco et al. 2005;Timofeeff et al. 2006), δ 37 Cl evolution curves of Cretaceous seawater should be discussed. ...
Late Cretaceous evaporite in the Khorat Plateau (KP) is one of the largest potash deposits in the world. Previous researches reported that the origin of potash deposits in the KP is controversial; however, recent studies emphasized non-marine fluids (hydrothermal fluid or meteoric water) influenced geochemical behaviors of potash deposits. Eleven halite samples from halite and potash layers in a drilling core (NS007) in southwestern KP were collected and analyzed for δ³⁷Cl values, Br⁻ and Cl⁻ concentrations in this study. The results show that (1) low δ³⁷Cl values (− 1.31‰ ~ + 0.14‰) of halite from halite layer, combining with reported isotopic (δD and δ¹⁸O) values of fluid inclusions in halite in corresponding layer, suggest possible influence of hydrothermal fluid; (2) positive correlation between δ³⁷Cl values and Br × 10³/Cl ratios, high δ³⁷Cl values (− 0.48‰ ~ + 0.41‰) and previous high ⁸⁷Sr/⁸⁶Sr values of halite from potash layer indicate meteoric water inputs into this layer. These comparisons demonstrate that hydrothermal or meteoric waters (non-marine fluids) influenced potash deposits in northeastern Thailand.
The salt lake of Sua Pan, one of the largest salt lakes in Botswana, is important resources of natural alkali. To identify the sources and genesis of subsurface brine in this salt lake, groundwater and surface water near this lake, in addition to subsurface brine water in the lake and salt crystals from solar salt field were collected and determined. The contents of major cation and anion, the isotope compositions of D, 18O and 37Cl, and the 14C age of groundwater were calculated. It is found that the subsurface brine is characterized by enriched Na and K, and depleted Ca and Mg. Results of D, 18O and 37Cl show that surface water is closely connected with subsurface brine in Sua Pan, while the role of groundwater recharge on it is weak (the difference of 37Cl is 0.04‰-0.06‰). Relationships of TDS-γNa/γCl indicate that leaching of halite affects the formation of this subsurface brine (γNa/γCl≈1), and the age of 14C (about 20 000 years ago)indicates that the fluctuation of ancient climate is considered to be an important factor of the formation of Sua Pan. Based on the above knowledge, inverse simulation of subsurface brine in Sua Pan is modeled by PHREEQC software, which further verifies that salt lake of Sua Pan is mainly the result of strong evaporation and concentration of surface water and halite leaching by groundwater.
Salt rock is mostly developed in Dongpu sag in Bohai Bay Basin, of which the Paleogene Shahejie Formation has mainly developed four sets of salt rocks with thickness of more than 1000 meters. However, there are many disputes on the origin of salt rock. Preliminary studies have been carried using sedimentological and geochemical methods. The salt rock has alternately developed with mud shale of layered sedimentary structure, and the average V/(V+Ni) ratio of mud shale is 0.736 (basically distributed within 0.64-0.81), which has developed halite hopper crystals mixed with sandy debris-flow massive sandstone; these features indicate the mud shale with layered sedimentary structure has been deposited in the strong reducing environment of deep to semi-deep lake. There is no exposed surface eroded between the salt rock and mud shale, and no mud crack structure in the mud shale layer; the salt rock is relatively pure with large thickness. Therefore, it can be concluded that the sedimentary environment of salt rock is the same as the adjacent mud shale, i. e., the strong reducing environment of deep to semi-deep lake. Vertically, the salt rock is developed in the lacustrine transgressive system tract and high stand system tract of sequence, and the development period of salt rock is also the main chasmic and expanding stage of Dongpu sag; horizontally, it is distributed in the center of the sag and has a reciprocal relationship with the sandstone deposited in the margin of the sag, whereas the mud shale is mainly distributed in the broad area between the sandstone and salt rock, i. e., depocenter of the salt rock is basically identical with deposition center and subsidence center of the sag. The development period of salt rock is also a peak period of the development of lake basin. Sedimentary evidences support the viewpoint of “salt deposited in deep water” for the salt rock of Dongpu sag. In the continuously deposited section of salt rock, δ37Cl values is not gradually decreasing from the old strata to the new, but showing irregular changes. These illustrate the salt rock of Paleogene Shahejie Formation of Dongpu sag should have developed in an environment with deep water under warm and wet weather, i. e., “salt deposited in deep water”. Moreover, it is illustrated through comparison with modern canyon lakes and artificial river reservoirs that Dongpu sag is obviously characterized by lake stratification during the development period of salt rock, providing the basis and basic form for “salt deposited in deep water”, and theoretically supporting the viewpoint of “salt deposited in deep water” for salt rock of Dongpu sag.
Brine from the saline Qarhan Lake was evaporated at 28±2°C in a clean environment. Two groups of experiments were conducted; one with complete separation of precipitate and brine at different stages of evaporation, and the other with continuous precipitation during the evaporation. Seventy-nine precipitate and brine samples were collected during the experiments, and the δ
37Cl values were determined using an improved thermal ionization mass spectrometry procedure for precise measurement of chlorine isotopes based on Cs2Cl+ ions. Based on the concentrations of Na+, K+, and Mg2+, evaporation was divided into three main precipitation stages as follows: halite dominant, carnallite dominant, and bischofite dominant. The δ
37Clsolid and δ
37Clliquid values of the precipitate and coexisting brine samples at different stages showed the following characteristics. The precipitates were enriched with 37Cl relative to the coexisting brine samples, and the δ
37Cl of both the precipitate and brine samples decreased gradually during evaporation. The fractionation factors (α
h) between halite and brine were the highest, followed by that (α
c) between carnallite and brine, and then that (α
b) between bischofite and brine. The α
c and α
b values of less than one, which indicate the precipitate is enriched in 35Cl, were found when the evaporation process entered a new stage. However, the δ
37Cl values of carnallite, bischofite, and the coexisting brine samples decreased during evaporation. The residual brine is a 35Cl reservoir. The experimental phenomena were consistent with the δ
37Cl values in saline deposits in the literature. δ
37Cl can be used as an indicator of brine evaporation processes, which is important in the exploration of sylvinite deposits.
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