Method for deep solid potash exploration prediction by using brine hydrogeochemistry simulation

Abstract

This invention provides a method for predicting deep solid potash deposits using brine hydrogeochemical simulation. The core of this method lies in using brine to locate potash. By simultaneously collecting surface saline spring water and deep borehole brine from the same target area, the method calculates and compares the brine characteristic coefficients of both. Based on this invention, a quantitative relationship of brine coefficient thresholds is proposed to determine the brine's formation, evaporation rate, and the influence of atmospheric precipitation. Brine samples indicating favorable deep potash-forming environments are screened. Then, a hydrogeochemical model is constructed and corrected, and the simulated evaporation mineral precipitation sequence is performed on the screened samples. The saturation indices of target minerals such as halite and carnallite are calculated. The core criterion is that the SI value of halite approaches -0.5 to +0.5, combined with the fact that halite is unsaturated and carnallite is nearly saturated. The exploration target area is delineated using a comprehensive multi-indicator approach. This invention aims to significantly improve the prediction accuracy and exploration efficiency of deep solid potash deposits under complex geological conditions.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, specifically providing a method for predicting deep solid potassium salt exploration using brine hydrogeochemical simulation. Background Technology

[0002] The Sichuan Basin is a famous large superimposed artesian basin in China, covering an area of ​​over 20 × 10⁻⁶. 4 km 2 The sedimentary strata are distributed across various formations from the Sinian to the Cretaceous, exhibiting a multi-yielding characteristic. The basin is generally subsided, with a complete sedimentary cover layer, totaling 6000-12000m in thickness. Basin water is distributed across 9 major halide-bearing rock systems and 21 regional brine layers, including 15 carbonate brine layers below the Upper Triassic and 6 clastic brine layers above the Middle Triassic.

[0003] The potassium, strontium, and magnesium-rich components in much of the ancient seawater in the Sichuan Basin primarily originated from the large-scale eruptions of the potassium-rich basalts of Mount Emei during the Late Permian. The pre-Middle Triassic sedimentary layers consisted of marine platform deposits dominated by carbonate rocks, 4000-7000 m thick, while the post-Middle Triassic layers were dominated by lacustrine-continental sediments, 2000-5000 m thick. Over its long geological evolution, the Sichuan Basin underwent multiple marine transgressions and regressions. During the Early to Middle Triassic, the basin was a semi-enclosed sea basin. The intrusion and retreat of ancient seawater, along with the large amounts of salt-bearing weathered material transported by surface runoff from the surrounding ancient landmasses, formed numerous salt lakes. Intense evaporation continuously concentrated the seawater in these ancient salt lakes, forming ancient brine. After the Late Triassic, thick layers of terrigenous clastic rocks formed a well-sealed layer, allowing the ancient brine to accumulate and be preserved. During the Indosinian and Himalayan orogenies, the Sichuan Basin underwent a transformation from a west-high to an east-high to a west-low pattern. Brine formation in the west occurred later than in the east, and the western part experienced a longer period of evaporation and concentration, resulting in a relatively higher degree of influence. The Caledonian and Early Indosinian orogenies formed paleo-uplifts in central Sichuan and the Luzhou-Kaijiang area, respectively, while the brine-bearing structures were finalized during the Himalayan orogeny. Because the Sichuan Basin is a complex basin composed of multiple tectonic systems, including compressional and compressional-shear structures, the burial conditions and formation / evolutionary experiences of the various brine layers differ, leading to variations in hydrochemical and isotopic geochemical characteristics and genetic types.

[0004] In mountainous areas, such as steep fold belts, the complex terrain and diverse geological structures make traditional prospecting methods difficult to implement. However, brine hydrogeochemical prospecting methods can analyze the content and distribution characteristics of elements in brine resources in mountainous areas, identifying geochemical anomalies related to ore bodies and thus providing clues for mineral exploration. In overburdened areas, ore bodies are often obscured by thick overburden layers, making direct detection difficult using traditional methods. Brine can penetrate overburden, carrying information about ore bodies. By analyzing the geochemical characteristics of the brine, ore bodies beneath overburdened areas can be effectively identified, providing new ideas and methods for mineral exploration in overburdened areas.

[0005] Traditional mineral exploration methods are often limited in detecting deep ore bodies, while brine can serve as a carrier of information about deep ore bodies. By analyzing the geochemical characteristics of exposed salt springs (salty springs) on the surface, relevant information about deep ore bodies can be obtained. Traditional mineral exploration methods, such as geological mapping, geophysical exploration, and drilling, are costly, inefficient, and have limited effectiveness in exploring deep or concealed deposits. Brine is an important ore-forming fluid, and its geochemical characteristics are closely related to mineral formation. Therefore, by simulating the geochemical evolution of brine, the distribution and enrichment patterns of solid potassium salts can be effectively predicted. In deep mineral exploration, brine hydrogeochemical prospecting has unique advantages. For example, in the exploration of some deep copper deposits, brine hydrogeochemical prospecting methods have successfully discovered deep copper ore bodies by analyzing the copper content and related geochemical indicators in deep brine, breaking through the depth limitations of traditional prospecting methods. Ore-forming elements in deep ore bodies can enter the brine through the circulation of groundwater, causing changes in the element content and distribution in the brine and creating geochemical anomalies. By identifying and analyzing these anomalies, the existence and location of deep ore bodies can be inferred.

[0006] The water in the brine originates from ancient seawater and the dehydration of minerals during salt formation. The hydrogen and oxygen isotopes in seawater are roughly consistent; the hydrogen isotope in potassium-rich brine is slightly lower than in seawater, while the oxygen isotope is higher, showing a close match. Seawater from different areas within the basin mixes and undergoes intense evaporation and concentration, remaining in sediments as crystal water, pore water, and fissure water. This process, combined with the long water-salinization process of later diagenesis and hydrocarbon accumulation, evolves into the present-day potassium-rich brine. Surface water dissolves and filters through pores or fissures into saline strata or mixes with other brines within the strata. Under gravity, it seeps downwards and migrates. The deeper the brine is deposited, the higher its concentration and density. Under the influence of high underground temperature and pressure, groundwater vaporizes, and deep brine concentrates due to evaporation, increasing its mineralization and leading to salinization and metamorphism.

[0007] In mineral exploration applications, the study of brine geochemical characteristics has identified several geochemical anomalies associated with mineralization. The Sichuan Basin has well-developed Mesozoic rock salt deposits and numerous saline springs exposed in the Triassic, exhibiting high total dissolved solids (TDS). The complexity of geological conditions presents numerous challenges to brine hydrogeochemical mineral exploration. Significant differences in geological structure, rock type, and stratigraphic conditions across different regions complicate the migration, enrichment, and transformation patterns of elements in the brine. In areas with well-developed fault structures, the flow path and chemical composition of the brine are affected, making the interpretation of geochemical anomalies difficult. Differences in rock type also influence the water-rock interaction between the brine and rocks, thus affecting the content and distribution of elements in the brine. The geochemical characteristics of brine differ significantly between igneous and sedimentary rock regions, requiring targeted analysis and research. Furthermore, stratigraphic variations and discontinuities further complicate the interpretation of brine geochemical characteristics, posing even greater challenges to mineral exploration. Summary of the Invention

[0008] The purpose of this invention is to provide a method for predicting solid potassium salts by using brine to locate potassium under complex geological conditions, based on a combination of brine characteristic coefficients and geochemical simulation evaporation experiments.

[0009] This invention provides a method for predicting deep solid potassium salt exploration using brine hydrogeochemical simulation, comprising the following steps: Surface saline spring water samples and borehole brine samples were collected and tested from the same target area, including: The surface saline spring water samples and borehole brine samples were analyzed. Both surface saline spring water samples and borehole brine samples underwent major and trace element analysis (K). + Na + Ca 2+ Mg 2+ Cl - SO4 2- CO3 2- HCO3 - ,Br - The test should simultaneously test the content of high-value elements such as B, Li, Rb, and Cs; hydrogen and oxygen isotope testing should only be performed on natural brine, and not on artificially dissolved brine.

[0010] Calculate three sets of indicator coefficients for the saline spring water sample and the borehole brine sample, respectively. The coefficients include the potassium chloride coefficient of 1000K / Cl and the bromine chloride coefficient of 1000Br / Cl. By comparing the corresponding values ​​of the potassium-finding indicator coefficient with those of the brine spring sample and the borehole brine sample, the formation of the brine can be determined to include primary and secondary processes. Furthermore, the formation of the brine can be determined to include sedimentary and leaching types. Finally, the potassium enrichment is analyzed. If so, it is determined that the borehole brine indicates the presence of a potassium-rich fluid environment at depth that is conducive to the formation and preservation of solid potassium salt deposits; Based on the constructed hydrogeochemical model, the saturation index of the target potassium salt minerals was calculated for borehole brine samples in potassium-rich fluid environments conducive to the formation and preservation of solid potassium salt deposits. Hydrogeochemical simulation was then conducted to establish an evaporation and precipitation sequence. The exploration target area is delineated based on whether the saturation index and evaporation precipitation sequence contain potassium salt.

[0011] Preferably, the target area for collecting surface salt spring water samples is determined based on at least one of the following geomorphological or geological features: the core of a steep anticline, a fault fracture zone or intersection zone, a stratigraphic contact zone, or the area surrounding an ancient salt well site.

[0012] Preferably, the at least one set of potassium-finding indicator coefficients further includes: bromine-chlorine coefficient 1000Br / Cl, sodium-chlorine coefficient nNa / nCl, magnesium-chlorine coefficient nMg / nCl, potassium-bromine coefficient K / Br, and potassium salt coefficient 1000K / nsalt; The sodium-chlorine ratio nNa / nCl is used to preliminarily identify the origin of brine: when the sodium-chlorine ratio of the borehole brine sample is between 0.85 and 0.87, it indicates that the brine has undergone strong dissolution and filtration; when the sodium-chlorine ratio is less than 0.85, it indicates that the brine has undergone positive metamorphism and is of sedimentary origin, and it is preliminarily judged that it is conducive to deep potassium formation.

[0013] Preferably, the potassium-finding indicator value of the borehole brine sample is compared with the corresponding value of the saline spring water sample to comprehensively judge and analyze the potassium-richness: The potassium-bromine coefficient K / Br value of the brine sample obtained from the borehole should be greater than 5.8.

[0014] Preferably, the method further includes the step of: calculating the desulfurization coefficient of the borehole brine sample; if the desulfurization coefficient of the borehole brine sample is close to 0, then it is confirmed that the sample is stored in a closed reducing environment. Furthermore, the borehole brine sample was diluted for verification: the borehole brine sample was mixed with fresh water until the mineralization was reduced by one order of magnitude, and its potassium-bromine coefficient was recalculated. If the change in the coefficient was less than 20%, it was confirmed that the potassium-bromine coefficient was not affected by atmospheric precipitation dilution and the obtained data was reliable.

[0015] Preferably, the process of constructing a hydrogeochemical model includes: establishing a regional geological concept model of the target area, wherein the model needs to clearly define the controlling factors of fluid sources, migration channels, reservoir space and enrichment mechanisms; Based on the measured chemical data of the borehole brine sample, the brine formation type and concentration stage parameters of the model were corrected by combining the values ​​of the sodium chloride coefficient nNa / nCl and the magnesium chloride coefficient nMg / nCl. When the measured bromine-chlorine coefficient 1000Br / Cl value of the borehole brine sample deviates from the brine type characteristics predicted based on the geological concept model, the parameter settings in the geological concept model regarding the formation dissolution intensity or fluid migration path are adjusted based on the deviation. When the hydrogen and oxygen isotope measurements of the natural brine do not match the predicted water source range based on the geological concept model, the constraints on the water source in the model shall be supplemented, and the constraints shall be at least the local atmospheric precipitation line. When performing hydrogeochemical simulations, the chemical data input into the model must include at least: K + Na + Ca 2+ Mg 2+ Cl - SO4 2- CO3 2- HCO3 - ,Br - The content of substances such as pH value and temperature.

[0016] Preferably, the target potassium salt minerals include potassium halite (KCl) and carnallite (KMgCl3·6H2O); The basic criterion for delineating exploration target areas based on saturation index is that the saturation index of potash is within the equilibrium range of -0.5 to +0.5.

[0017] Preferably, the basic criterion also needs to be satisfied together with the following conditions to constitute a higher-order comprehensive criterion: The saturation index of halite (NaCl) is less than 0; the saturation index of carnallite is greater than -1.0.

[0018] Preferably, before delineating the target area, the reverse simulation function of PHREEQC software is used to simulate the dissolution path of the borehole brine components and potential solid potassium salt minerals. If the simulation results are feasible, the reliability of the target area is verified in reverse.

[0019] The beneficial effects of this invention are as follows: by utilizing the hydrogeochemistry of brine in mountainous areas and covered areas, the characteristic properties of brine are determined by establishing the element content and characteristic coefficients of brine in adjacent salt springs and boreholes, evaporation crystallization salt precipitation law and evolution process of evolution crystallization route, and the distribution and enrichment areas of potential minerals are predicted, thereby improving the efficiency and success rate of mineral exploration. Attached Figure Description

[0020] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Furthermore, similar numbers in the drawings are used to denote similar components, wherein: Figure 1To determine the potassium enrichment level using the ion ratio coefficient in one embodiment of the present invention; Figure 2 This is a simplified diagram illustrating the differentiation between sedimented brine and dissolved brine according to an embodiment of the present invention; Figure 3 This is a pipe diagram illustrating the composition of deep brine in a certain region according to an embodiment of the present invention; Figure 4 This is a simulation of the evolution of brine at 25°C in a closed system according to an embodiment of the present invention. Detailed Implementation

[0021] Some embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0022] like Figure 1-4 As shown, this invention provides a method for predicting deep solid potassium salt exploration using brine hydrogeochemical simulation, comprising: Step S1, Data Acquisition or Collection and Analysis: The geological features of eastern Sichuan are characterized by "barrier folds," consisting of a series of parallel, steep anticlines (mountains) alternating with broad, gentle synclines (valleys). Considering that the formation of saline springs in the Sichuan Basin involves atmospheric precipitation infiltration, groundwater runoff, and eventual emergence as springs in suitable terrain, the focus of spring location should be concentrated in anticline mountain areas. Generally, highly mineralized brine springs are historically known by place names such as "Yanjin" or "Yantan." Here, our sampling criteria are based on the presence of a salty taste, regardless of mineralization. Sampling includes both surface and underground brine. Detailed geological, hydrogeological, and geochemical data for the study area are collected, including but not limited to: the chemical composition of the brine (major cations, anions, trace elements, etc.); the mineral composition and chemical composition of rocks and minerals; and hydrogeological parameters (such as permeability and porosity). Advanced analytical techniques such as inductively coupled plasma mass spectrometry (ICP-MS) are used to accurately determine the chemical composition of the brine and rocks (Table 1).

[0023] Table 1. Methods for collecting and collecting potentially potassium-rich brine samples

[0024] Step S2: Analysis of brine characteristic coefficients (1) Establish a geological conceptual model. First, a clear geological conceptual model is needed. Then, the geochemical model is corrected using measured brine chemical composition data to ensure that the model can accurately reflect the actual situation of the study area.

[0025] There are also cases where the potassium ion content, potassium-chlorine coefficient, and bromine-chlorine coefficient of brine are much lower than those of borehole water, while the mineralization is basically the same. If we do not consider the origin of the brine, we will conclude that the possibility of finding potassium is not as good as that of borehole water (Table 2).

[0026] Table 2. Degree of brine concentration

[0027] First, a clear geological conceptual model is needed. Then, measured brine chemical composition data are used to calibrate the geochemical model to ensure that the model accurately reflects the actual situation of the study area. The construction of the geological conceptual model needs to take into account the regional tectonic evolution, stratigraphic development characteristics, fluid migration channels, and mineralization environment background, and clarify the core controlling factors of each link of "source-migration-reservoir-enrichment". For the Tianxingqiao tectonics in northeastern Sichuan, a geological conceptual model of "atmospheric precipitation-tectonic fracture migration-Cambrian saline strata dissolution-anticline tectonic reservoir" needs to be constructed. For the Lower Yangtze Block, a marine model framework of "sedimentary sequestration-atmospheric precipitation mixing-evaporation concentration-porosity reservoir enrichment" needs to be established.

[0028] (2) Determine the hydrochemical characteristic coefficients of brine formation.

[0029] Direct indicators of potassium richness in brine include the 1000K / η coefficient and the 1000K / Cl coefficient, while indirect indicators of potassium richness include the 1000Br / Cl, nNa / nCl, nMg / nCl, and K / Br coefficients. Figure 1 (See Table 3). These characteristic values ​​may decrease in surface salt springs due to long-distance brine transport. The characteristic values ​​are mainly determined based on seawater evaporation and artificial brine filtration experiments, and should only be used as a reference.

[0030] Different coefficients require comprehensive analysis to draw scientific conclusions. Most coefficients revolve around Cl. - Use Cl as the denominator because -The brine evolution is the most conservative (almost never entering the solid phase). Based on these characteristic coefficients and other geological data, it is inferred that the salt source depression may contain abundant salt mineral deposits, and the salt spring water samples may be peripheral salt spring water from deep potassium-magnesium salt deposits, with the deep salt material likely originating from Cambrian rock salt layers. Based on the geological conceptual model, an initial geochemical model was constructed using brine hydrogen and oxygen isotopes and the 1000Br / Cl value as core indicators, integrating auxiliary indicators such as 1000K / Cl and isotopes to clarify the response relationship between each indicator and the mineralization process. Subsequently, the parameters in the initial model were iteratively corrected using measured brine chemical composition data collected by the system. If the measured 1000Br / Cl value deviates from the model's predicted characteristics of leaching brine, it is necessary to retrospectively examine the settings for strata leaching intensity in the geological conceptual model and adjust the fluid transport path parameters in conjunction with tectonic history. If the hydrogen and oxygen isotope plots do not match the model's predicted water source range, it is necessary to re-examine the impact of paleoclimate evolution on precipitation replenishment and supplement the constraints on potential water sources such as magmatic hydrothermal fluids and paleoseawater.

[0031] Table 3 Characteristic coefficients and anomaly level index system of Haiyuan brine

[0032] *Ⅰ - Abnormal (halite), Ⅱ - Obvious abnormal (potassium-containing halite), Ⅲ - Reached the potassium-magnesium salt deposition stage First, it is necessary to determine whether the brine is of primary or secondary origin, either sedimentary or leached ①②③, and then use coefficients ①⑥⑦ for further judgment. Then, use ⑧ and commonly used potassium-finding indicators ①⑥ for verification. For closed-loop utilization ④, the influence of atmospheric precipitation desalination on utilization ⑤ is also considered. The comprehensive and coordinated use of core indicators ultimately forms a multi-indicator cross-verified mineralization model, which can achieve full-chain constraints of "genesis-evolution-mineralization," significantly improving the reliability of target area delineation.

[0033] ① The bromine-chlorine coefficient is 1000 (Br / Cl or Cl / Br weight ratio). This is indicative of brine formation and can distinguish between dissolved brine and sedimentary brine. It is the ratio of bromide ions (Br⁻) in the brine. - ) and chloride ions (Cl - The ratio of bromine content (bromine content multiplied by 1000) to chlorine content is an important indicator in the fields of hydrogeochemistry and resource exploration.

[0034] Tracing the origin and source of brine: Brine from different sources has characteristic bromine-chlorine coefficient ranges; the ratio of dissolved brine will show a specific range depending on the type of dissolved minerals (such as halite, potassium-containing halite), which can be used to distinguish primary sedimentary brine, dissolved brine, etc. Indicating the brine evolution process: This ratio reflects the degree of brine evaporation and concentration, the intensity of water-rock interaction, and the mixing process. For example, when extreme evaporation does not reach halite saturation, the ratio is relatively stable; if formation leaching, hydrothermal doping, or other effects occur, the ratio will show abnormal fluctuations.

[0035] Auxiliary resource exploration is a key indicator for the exploration of brine resources such as salt and potash mines. For example, in the search for potash in marine evaporite basins, the 1000Br / Cl value, together with indicators such as 1000K / Cl and K / Br, constitute a potash-finding indicator system, which can determine whether the brine dissolves potassium-containing minerals and provide a basis for the search for solid potash salt mines.

[0036] ② nNa / nCl molar ratio. Used to identify the origin of brine. The normal nNa / nCl molar ratio of seawater is approximately 0.85-0.87. This ratio can be used to distinguish brines of different origins. If the ratio is significantly higher than 0.86, it often indicates that the brine has undergone intense leaching, such as the leaching-type potassium-rich brine of the Tianxingqiao structure in northeastern Sichuan. This high ratio can corroborate its origin as "leaching of saline strata by atmospheric precipitation." If the ratio is lower than 0.86, it may be due to Na concentration during evaporation. + Through cation exchange (such as with Ca in the formation) 2+ (Exchange) loss, or contamination with Cl-rich substances - The deep hydrothermal fluids can help rule out the possibility of marine primary sedimentary brine as the cause.

[0037] Reversing the brine evolution process. During the evaporation and concentration stage, as the evaporation intensity increases, Cl... - The enrichment rate is faster than that of Na + The ratio will gradually decrease. Combined with the evaporation-concentration mineralization model of lithium-rich brines in the Lower Yangtze Block, the fluctuation of this ratio can be used to determine the strength and stage of evaporation, thus identifying key areas of evaporation enrichment. Regarding water-rock interaction, if cation exchange occurs between the brine and clay minerals during brine migration, Na... + Adsorption causes a decrease in the ratio, which can be used to trace the migration path of the brine.

[0038] ③ The magnesium-chlorine coefficient, nMg / nCl molar ratio. Mg 2+ The nMg / nCl molar ratio exhibits strong stability during brine evaporation, with characteristic ranges observed at different evaporation stages. The ratio remains relatively stable in the early evaporation stages; a sudden drop in the ratio may indicate the precipitation of minerals such as gypsum and esperidium, which can help determine the paleothermal aridity of mineralization. The magnesium-chlorine coefficient of seawater is 0.13, while the coefficient of brine is 0.16 when gypsum begins to deposit. As seawater concentrates, the magnesium-aluminum coefficient continuously increases, reaching 0.75 when potassium salts begin to deposit. This ratio shows significant differences between terrestrial salt lakes and marine sedimentary brines, which can be further differentiated from terrestrial dissolution and marine sedimentary origins by combining the 1000Br / Cl value.

[0039] ④ Desulfurization coefficient (DSC) = SO42- ×100 / Cl. The smaller the desulfurization coefficient, the better the environmental enclosure and the stronger the reducing power of the brine. This is because in a closed reducing environment, sulfates are reduced to hydrogen sulfide (H2S) by desulfurization bacteria, leading to SO42-. 2- Reduce reaction equation: SO4 2- +2C+ 2H2O→H2S + 2HCO3 - The conditions for saving are: DSC<1: This indicates that the formation water is completely reduced and well sealed, which is beneficial to the preservation of minerals such as oil and gas. DSC>1: This indicates that the reduction process was incomplete and may be affected by shallow oxidation. DSC≈0: This indicates a highly enclosed environment with extremely strong reducing properties, commonly found in deep brine.

[0040] ⑤ δ D and δ 18 The main functions of hydrogen and oxygen isotopes in brine include: tracing the source of brine, distinguishing whether it originates from atmospheric precipitation, ancient seawater, magmatic water, or formation water; reflecting the brine formation environment, such as the temperature of the sedimentary environment, evaporation intensity, and recharge and discharge conditions; tracing the evolution of brine, revealing its mixing, evaporation and concentration, and water-rock interaction processes in geological history; and guiding resource exploration, assisting in the search for brine-related mineral resources such as potash and oil and gas.

[0041] The hydrogen and oxygen isotopes in the Middle and Lower Triassic brine of the Sichuan Basin are respectively δ D = -119.5‰ δ 18 O = -15.2‰, indicating that its water source is mainly rainfall and the flow process is relatively long. The hydrogen and oxygen isotopes of atmospheric precipitation in the Sichuan Basin are... δ D=-57‰, δ 18 O = -8.7‰. Global precipitation line. δ 2 H=8 δ 18 O+10; Chongqing Atmospheric Precipitation Line δ 2 H=8.73 δ 18 O+15.73; China's atmospheric precipitation line δ 2 H= δ 18 O+10.

[0042] ⑥1000K / Cl and ⑦potassium salt coefficient K×10 3 / Ʃsalt (Ʃsalt is the total salt content) weight ratio. The potassium salt coefficient represents the percentage of potassium in the total salt content of brine, and it is the most direct mineral exploration indicator in dissolved brine. Analysis of potassium salt anomalies and brine concentration shows that a high potassium ion content in the water is a good indicator for potassium exploration. When using mineralization as a hydrochemical indicator for potassium exploration, it is generally believed that the higher the mineralization, the more favorable it is for potassium exploration. However, due to different hydrogeological conditions, sedimentary environments, and surrounding rocks, the potassium ion content in the water varies greatly, making it difficult to apply accurately.

[0043] ⑧ K / Br weight ratio coefficient. The lower limit of the K / Br anomaly value in seawater is 5.8. Desalination of highly mineralized water has virtually no effect on the potassium-bromine ratio. It is ideal as a marker for potassium in water chemistry, a particularly sensitive indicator for revealing dissolved potassium salts, unaffected by desalination, and can detect anomalies even when the origin is unclear. When brine evaporates and concentrates to the point where potassium salts begin to precipitate, potassium salts gradually precipitate from the brine. As a large amount of potassium salts precipitate, the K in the brine... + The content of potassium chloride decreases, while the content of bromine in the brine increases. Bromine does not form a separate mineral but rather precipitates as an isomorphous mixture with all chlorides. The partition coefficient of bromine between the crystals and solution is less than 1, meaning less bromine enters the solid phase than remains in the solution. The ratio K / Br only exceeds 5.8 after potassium salts are dissolved. Desalination of highly mineralized water has virtually no effect on the potassium-bromine ratio. For example, in a desalination experiment conducted on brine samples from a brine well in a region in Southwest China, the ratios of brine to fresh water were 1:1, 1:3, 1:7, 1:15, 1:31, 1:63, and 1:127 (Table 3).

[0044] Table 4. Experiments on mixing high-mineralized brine and fresh water at different ratios

[0045] Step S3: Determination of water chemistry type and saturation index In the practical application of "finding potassium through brine," potassium salt minerals (such as halite and carnallite) have extremely high solubility. The discrimination logic involves analyzing the chemical composition of deep brine samples and using thermodynamic data to calculate the saturation index (SI) of specific minerals.

[0046] The saturation index (SI) of various chemical substances was calculated using the geochemical simulation software PHREEQC. If the dissolution rate exceeds the diffusion migration from the interface into the water, saturation occurs near the interface, leading to an exponential decrease in saturation with increasing distance from the interface. This dissolution is considered to be controlled by the solubility product. If the dissolution rate is less than the diffusion migration, saturation is not reached, indicating diffusion-controlled dissolution.

[0047] The saturation index calculated using Phreeqc has a certain margin of error. Therefore, when the saturation index SI of a certain mineral is ±0.5, the mineral is considered saturated in solution. If SI < 0 (unsaturated): This indicates that the brine is in the dissolution stage, meaning that the minerals have not reached saturation in the aqueous solution and will continue to dissolve. The minerals may be located on the periphery or in the recharge zone of the potash ore body.

[0048] If SI≈0 (equilibrium state): This indicates that the brine and potassium salt minerals have reached a two-phase equilibrium, and the minerals are in equilibrium in the aqueous solution, indicating that there is a high probability of a hidden solid potassium salt mineral body near the sampling point.

[0049] When SI > 0, it indicates that the mineral is in a supersaturated state in the aqueous solution and the mineral will precipitate.

[0050] To further explain Ca 2+ Mg 2+ HCO3 - and SO4 2- The relationship between the minerals and the equilibrium state of other trace elements in aqueous solution was investigated. The saturation index (SI) of relevant minerals was determined using PHREEQC, and the results are shown in the table. The saturation indices of minerals such as calcite, dolomite, gypsum, anhydrite, halite, and potassium halite in the saline springs indicate that the minerals in the saline springs of the study area are in an unsaturated state, suggesting that the carbonate rock minerals in the solution are in equilibrium or undergoing sedimentation. Step S4: Hydrogeochemical EVP / EQL Evaporation Simulation Experiment Elements from brine springs and borehole brines are input in molar concentration units. The output of EVP / EQL focuses on intuitive predictions of mineral precipitation sequences and solute changes. Based on EQL / EVP, a program simulating water evaporation to high salinity is used, with isothermal evaporation experimental temperatures set at 25°C and 50°C; the system is configured as a closed system.

[0051] Step S5, Mineral Prediction and Exploration: Utilizing the fundamental principle that brine composition is unaffected by desalination, this study predicts mineral distribution and enrichment areas, and simulates the evolution of brine under different temperature conditions.

[0052] The following example, using the exploration of potash in an ancient salt lake in southwestern China, illustrates the specific implementation of this invention: Data Acquisition and Analysis: Hydrochemical composition data, rock and mineral data, geological parameters, and hydrogeological parameters were collected from the salt spring brine (CQLS-8) and artificially filtered brine (drill holes YZ1, YP1, Y5). The contents of elements such as Li, K, Mg, and Na in the brine were accurately determined using ICP-MS.

[0053] CQLS-8 Salt Spring ⑦ 1000K / Ʃ Salt Calculation Process: Mass of 1L solution: 1.0125 × 1000 = 1012.5 g / L·K + Concentration: 1012.5 × 0.09% ÷ 100 = 0.91125 g / L·ΣSalt (TDS) = (1012.5 × (0.09 + 0.002 + 0.41 + 0.003 + 0.0027 + 0 + 0.100 + 0.21)% ÷ 100) + (24 + 2.25 + 1.5 + 16.25) ÷ 1000 = 8.323 g / L·Potassium enrichment per thousand: 1000 × 0.91125 ÷ 8.323 ≈ 109.5 Judgment result: WLS salt spring is dissolved brine.

[0054] Table 5. Hydrochemical Analysis of Salt Spring Brine and Artificially Dissolved Brine

[0055] CQLS-8 is brine from a salt spring; YZ1, YP1, and Y5 are artificially filtered brine. The characteristic coefficients and saturation indices of the sedimentary evaporites CQLS-8, YZ1, YP1, and Y5 were calculated (Tables 2 and 3).

[0056] Table 2 Characteristic values ​​of salt spring brine and artificially dissolved brine

[0057] CQLS-8, YZ1, YP1, and Y5: ①③⑥⑦⑧ indicate the potassium-magnesium salt deposition stage; ④DSC<1 indicates that the formation water is completely reduced and well sealed, indicating that the brine is stored in a closed environment; ② is the discriminant value and is ignored.

[0058] Table 3 Saturation index of the main salt minerals in WLS brine

[0059] The basin's specific conditions for potassium preservation are highly favorable for the formation and enrichment of liquid potassium salts, providing excellent space for brine accumulation. Typically, in areas favorable for potassium formation, the uplifted parts of local structures and the fault zones of anticlines, with their well-developed fissures and pores, provide ideal spaces for brine accumulation, forming brine enrichment zones. Using measured brine chemical composition data, the geochemical model was corrected to predict the distribution and enrichment of solid potassium salts in this area.

[0060] According to the Piper diagram, the diamond-shaped areas represent predominantly cationic substances in the water, such as sodium, potassium, and calcium, while the triangular areas represent predominantly anionic substances. The brine's chemical characteristics are Cl-Na or Cl-Na·Ca type. This study used the EQL / EVP brine chemical equilibrium model in a closed system (CQLS-8). The simulation temperature was t=25℃; based on previous research, the partial pressure of carbon dioxide, P, was set. CO2 =10 -3,4 The simulated precipitated mineral sequence results are as follows, see below. Figure 3 .

[0061] 1 Calcite 2 Calcite + Magnesite 3 Calcite + Magnesite + Soda 4 Calcite + Magnesite + Sodastone + Lithium Carbonate 5 Calcite + Magnesite + Sodastone + Lithium Carbonate + Potassium salt 6 Calcite + Magnesite + Sodastone + Lithium Carbonate + Potassium salt Potassium bicarbonate Simulation results show that the minerals precipitated in this system mainly include calcite, magnesite, potassium mirabilite, halite, and potassium halite. The potassium-bearing minerals are primarily potassium halite; lithium carbonate and sodium lithium sulfate are also present. Based on a comprehensive assessment of regional geological and hydrogeological data, it is determined that solid potassium halite exists in this area.

[0062] Based on the potassium ion contents of the artificially dissolved brine boreholes YZ1, YP1, and Y5, which are 0.51%, 0.46%, and 0.49%, respectively, it is determined that there is solid potassium halite in the deep part of this area.

[0063] This invention provides a method for predicting deep solid potash exploration using brine hydrogeochemical simulation. This method can improve the efficiency and success rate of mineral exploration and has significant application value. Through geochemical simulation, enrichment areas of elements can be predicted, thereby guiding mineral exploration.

[0064] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the original technical features, and the technical solutions resulting from these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for predicting deep solid potassium salt exploration using brine hydrogeochemical simulation, characterized in that, Includes the following steps: Surface saline spring water samples and borehole brine samples were collected and tested from the same target area, including: The surface saline spring water samples and borehole brine samples were analyzed. Both surface saline spring water samples and borehole brine samples underwent major and trace element analysis (K). + Na + Ca 2+ Mg 2+ Cl - SO4 2- CO3 2- HCO3 - ,Br - Test B should be tested simultaneously. 3+ Li + 、Rb + Cs + High-value element content; hydrogen and oxygen isotope testing is only performed on natural brine, and not on artificially dissolved brine. Calculate three sets of indicator coefficients for the saline spring water sample and the borehole brine sample, respectively. The coefficients include the potassium chloride coefficient of 1000K / Cl and the bromine chloride coefficient of 1000Br / Cl. By comparing the corresponding values ​​of the potassium-finding indicator coefficient with those of the brine spring sample and the borehole brine sample, the formation of the brine can be determined to include primary and secondary processes. Furthermore, the formation of the brine can be determined to include sedimentary and leaching types. Finally, the potassium enrichment is analyzed. If so, it is determined that the borehole brine indicates the presence of a potassium-rich fluid environment at depth that is conducive to the formation and preservation of solid potassium salt deposits; Based on the constructed hydrogeochemical model, the saturation index of the target potassium salt minerals was calculated for borehole brine samples in potassium-rich fluid environments conducive to the formation and preservation of solid potassium salt deposits. Hydrogeochemical simulation was then conducted to establish an evaporation and precipitation sequence. The exploration target area is delineated based on whether the saturation index and evaporation precipitation sequence contain potassium salt.

2. The method according to claim 1, characterized in that, The target area for collecting surface salt spring water samples is determined based on at least one of the following geomorphological or geological features: the core of a steep anticline, a fault fracture zone or intersection zone, a stratigraphic contact zone, or the area surrounding an ancient salt well site.

3. The method according to claim 1 or 2, characterized in that, The at least one set of potassium-finding indicator coefficients also includes: bromine-chlorine coefficient 1000Br / Cl, sodium-chlorine coefficient nNa / nCl, magnesium-chlorine coefficient nMg / nCl, potassium-bromine coefficient K / Br, and potassium salt coefficient 1000K / nsalt; The sodium-chlorine ratio nNa / nCl is used to preliminarily identify the origin of brine: when the sodium-chlorine ratio of the borehole brine sample is between 0.85 and 0.87, it indicates that the brine has undergone strong dissolution and filtration; when the sodium-chlorine ratio is less than 0.85, it indicates that the brine has undergone positive metamorphism and is of sedimentary origin, and it is preliminarily judged that it is conducive to deep potassium formation.

4. The method according to claim 3, characterized in that, The potassium-finding indicator coefficient value of the borehole brine sample is compared with the corresponding value of the saline spring water sample to comprehensively judge and analyze the potassium-richness: The potassium-bromine coefficient K / Br value of the brine sample obtained from the borehole should be greater than 5.

8.

5. The method according to claim 1, characterized in that, The method also includes the step of: calculating the desulfurization coefficient of the borehole brine sample; if the desulfurization coefficient of the borehole brine sample is close to 0, it is confirmed that the sample exists in a closed reducing environment. Furthermore, the borehole brine sample was diluted for verification: the borehole brine sample was mixed with fresh water until the mineralization was reduced by one order of magnitude, and its potassium-bromine coefficient was recalculated. If the change in the coefficient was less than 20%, it was confirmed that the potassium-bromine coefficient was not affected by atmospheric precipitation dilution and the obtained data was reliable.

6. The method according to claim 1, characterized in that, The process of constructing a hydrogeochemical model includes: establishing a regional geological concept model of the target area, which needs to clearly define the controlling factors of fluid sources, migration channels, reservoir space and enrichment mechanisms; Based on the measured chemical data of the borehole brine sample, the brine formation type and concentration stage parameters of the model were corrected by combining the values ​​of the sodium chloride coefficient nNa / nCl and the magnesium chloride coefficient nMg / nCl. When the measured bromine-chlorine coefficient 1000Br / Cl value of the borehole brine sample deviates from the brine type characteristics predicted based on the geological concept model, the parameter settings in the geological concept model regarding the formation dissolution intensity or fluid migration path are adjusted based on the deviation. When the hydrogen and oxygen isotope measurements of the natural brine do not match the predicted water source range based on the geological concept model, the constraints on the water source in the model shall be supplemented, and the constraints shall be at least the local atmospheric precipitation line. When performing hydrogeochemical simulations, the chemical data input into the model must include at least: K + Na + Ca 2+ Mg 2+ Cl - SO4 2- CO3 2- HCO3 - ,Br - The content of substances such as pH value and temperature.

7. The method according to claim 6, characterized in that, The target potassium salt minerals include potassium halite (KCl) and carnallite (KMgCl3·6H2O); The basic criterion for delineating exploration target areas based on saturation index is that the saturation index of potash is within the equilibrium range of -0.5 to +0.

5.

8. The method according to claim 7, characterized in that, The basic criterion must also satisfy the following conditions to constitute a higher-order comprehensive criterion: The saturation index of halite (NaCl) is less than 0; the saturation index of carnallite is greater than -1.

0.

9. The method according to claim 8, characterized in that, Before delineating the target area, the reverse simulation function of PHREEQC software is used to simulate the dissolution path of the borehole brine components and potential solid potassium salt minerals. If the simulation results are feasible, the reliability of the target area is verified in reverse.

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