Method for measuring element distribution coefficient and isotope fractionation value between fluid and melt
By conducting isotope exchange reactions in a high-temperature, high-pressure autoclave and combining them with liquid nitrogen cryogenic separation technology, the problem of determining the elemental partition coefficient and isotope fractionation value between fluids and silicate melts has been solved, achieving efficient separation and accurate measurement, and supporting magma-fluid research.
Patent Information
- Application Number
- CN202610011509.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-06
- Publication Date
- 2026-03-27
AI Technical Summary
Existing technologies are difficult to efficiently determine the elemental partition coefficients and isotopic fractionation values between fluids and silicate melts, especially under high temperature and high pressure conditions, where sample separation and measurement are challenging.
A salt solution was prepared as the initial fluid, and a silicate melt with added metal elements was used as the initial solid phase. A high-temperature and high-pressure isotope exchange reaction was carried out. The experiment was conducted in a quenched and cold-sealed autoclave. Combined with liquid nitrogen freezing separation and multi-step deionized water washing, the fluid phase and melt phase were accurately separated. The elemental content and isotopic composition were determined by inductively coupled plasma mass spectrometry.
It achieves efficient separation and accurate measurement of fluid and melt phases, with a sample recovery rate of ≥95% and long-term accuracy of isotopic composition analysis better than ±0.05‰, supporting the development of magma-fluid related research.
Smart Images
Figure CN121740549A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of stable isotope geochemistry, and specifically relates to a method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a silicate melt. Background Technology
[0002] There are differences in nuclear mass between isotopes. Through physical, chemical, or biological processes, the stable isotopic composition of a system (e.g., 18 O / 16 The abundance ratio of O will undergo a slight change, known as isotopic fractionation. Stable isotope geochemistry, which focuses on stable isotope analysis methods, compositional characteristics, fractionation mechanisms, and tracer applications, is one of the important cornerstones of modern earth science.
[0003] Stable metal isotopes are a novel approach for studying magmatic-hydrothermal systems, contributing to an understanding of the genetic link between fluid-related mineral deposits and magmatic-hydrothermal processes. The fractionation coefficients of stable metal isotopes between fluids and silicate magmas are a prerequisite for related research, and high-temperature, high-pressure (HTHP) experiments are currently almost the only method for determining isotopic fractionation coefficients in magma-fluid systems. HTHP studies are technically very challenging, requiring the determination of magma-fluid isotopic equilibrium, overcoming the complexation of metal and precious metal reaction vessels in the sample, effective separation of the two phases after experimental quenching, and precise measurement of the isotopic composition of the fluid and the quenched melt.
[0004] Therefore, it is necessary to provide a method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a silicate melt. Summary of the Invention
[0005] To address the aforementioned problems, this application provides a method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt, comprising: preparing a salt solution as the initial fluid; The silicate melt with added metal elements was used as the initial solid phase; The initial fluid and initial solid phase are welded and sealed in a sample tube, which is then placed in a quenched and cold-sealed autoclave for isotope exchange reaction. The reaction is carried out for 1-40 days at a temperature of 700-900℃ and a pressure of 1.8-2.2kbar. The sample tube after the reaction was quenched and frozen in sequence and then restored to room temperature. The sample tube was opened and the solution inside was taken out. The inside of the sample tube was washed with deionized water to obtain a cleaning solution. The cleaning solution was mixed with the taken-out solution as the experimental fluid phase. The remaining solid in the sample tube was collected as the experimental melt phase. The metal element content and stable isotope composition of the experimental fluid phase and experimental melt phase were determined, and the metal element partition coefficient and its isotope fractionation value between the experimental fluid phase and the experimental melt phase were calculated.
[0006] Furthermore, the molar ratio of NaCl to KCl in the salt solution is (0.5-1.5):(0.5-1.5), and the total concentration of Na and K in the salt solution is 0.5-1.5 mol / L.
[0007] Furthermore, the metallic elements include Ba, Sr, and Mg.
[0008] Furthermore, the silicate melt includes at least one of pure silicate melt, fluorinated silicate melt, and sulfur-containing silicate melt.
[0009] Furthermore, the pure silicate melt is prepared by grinding and mixing analytically pure SiO2, Al(OH)3, Na2CO3, K2CO3 and nitrates corresponding to metal elements, heating to decarburize, and melting and quenching, with an aluminum saturation index of 0.8-1.2. Fluorosilicate melts are prepared by grinding and mixing analytically pure SiO2, Al(OH)3, Na2CO3, K2CO3, and nitrates corresponding to metal elements, followed by heating to decarburize, melting and quenching, and then mixing in NaF. The aluminum saturation index is 0.8-1.2, and the mass percentage of fluorine in the fluorosilicate melt is 1-5%. The sulfur-containing silicate melt is prepared by grinding and mixing analytically pure SiO2, Al(OH)3, Na2CO3, K2CO3 and nitrates corresponding to metal elements, heating and decarburizing, melting and quenching, and then mixing in Na2SO4. The aluminum saturation index is 0.8-1.2, and the mass percentage of sulfur in the sulfur-containing silicate melt is 1-5%.
[0010] Furthermore, the initial fluid and initial solid phase are welded and sealed in a sample tube, which is then placed in a cold-sealed autoclave for isotope exchange reaction, including: Monitor the temperature and pressure during the isotope exchange reaction process, controlling the temperature uncertainty to within 5℃ and the pressure uncertainty to within 30 bar.
[0011] Furthermore, by measuring the metal element content and stable isotope composition of the experimental fluid phase and experimental melt phase under different isotope exchange reaction times, it was determined whether the isotope exchange reaction reached element / isotope exchange equilibrium, and the isotope exchange reaction time was optimized.
[0012] Furthermore, the metal element content and stable isotopic composition of the experimental fluid phase and experimental melt phase were determined, including: After the experimental fluid phase was evaporated to dryness, it was dissolved in acid to prepare a fluid phase solution. A portion of the solution was then taken out and the metal element content was determined by inductively coupled plasma mass spectrometry. A portion of the experimental melt phase was used to make a target with epoxy resin. After grinding and polishing, the metal element content was determined by laser ablation inductively coupled plasma mass spectrometry. The other portion was crushed, washed with deionized water and dried, and then dissolved in acid to prepare a melt phase solution. The metal elements in the residual fluid phase solution and the melt phase solution are separated from other matrix elements by using a cation exchange resin to obtain a first pure metal element solution in the residual fluid phase solution and a second pure metal element solution in the melt phase solution. The stable isotopic composition of the first and second pure metal solutions was determined by multi-receiver inductively coupled plasma mass spectrometry.
[0013] Furthermore, the mass fractionation caused by multi-receiver inductively coupled plasma mass spectrometry was corrected using a double diluent method.
[0014] Furthermore, the metal element partition coefficients and their isotopic fractionation values between the experimental fluid phase and the experimental melt phase are calculated, including: Divide the measured concentration of metal elements in the fluid phase solution by the concentration of metal elements in the experimental melt phase to obtain the metal element partition coefficient between the experimental fluid phase and the experimental melt phase. The isotopic fractionation values between the experimental fluid phase and the experimental melt phase are obtained by subtracting the measured values of the stable metal isotopic composition of the first and second pure metal solutions.
[0015] Compared with the prior art, this application has the following advantages: This application involves separating the fluid phase and silicate phase by liquid nitrogen freezing after isotope exchange equilibrium in a rapidly quenched, cold-sealed autoclave, followed by multi-step deionized water washing. The fluid phase and silicate phase are then precisely separated and recovered, and their elemental content and isotopic composition are accurately analyzed. This has positive implications for the development of isotope geochemistry.
[0016] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1A flowchart illustrating a method for determining the elemental distribution coefficient and isotopic fractionation value between a fluid and a melt, according to an embodiment of this application, is shown. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0020] Example 1 like Figure 1 As shown, a method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt includes the following steps:
[0021] S1: The hydrothermal fluids that are in direct equilibrium with magma in nature are mainly aqueous solutions containing NaCl and KCl. The initial fluids in the initial materials of the high temperature and high pressure experiment were prepared using deionized water and analytical grade NaCl and KCl. The total concentrations of Na and K in the salt solution were 0.5 mol / L, 1 mol / L and 1.5 mol / L, respectively, and the molar ratio of NaCl to KCl was 1:1.
[0022] Since the temperature limit of the quenched and sealed high-pressure autoclave is 900℃, and most of the fluid exsolution is related to felsic melt in the late stage of magma evolution, a synthetic silicate melt with a composition similar to "light granite" was used as the initial solid phase.
[0023] Silicate melts include pure silicate melts, fluorinated silicate melts, and sulfur-containing silicate melts.
[0024] Pure silicate melt containing Ba was prepared by grinding and mixing analytically pure SiO2, Al(OH)3, Na2CO3, K2CO3, and Ba(NO3)2 powders in an agate mortar, followed by decarburization at 1100℃, melting at 1600℃, and quenching. Using the same components of the pure silicate melt, fluorine-containing silicate melt and sulfur-containing silicate melt were obtained as the initial solid phase by adding analytically pure NaF or Na2SO4 powder, respectively. In a pure silicate melt raw material with an aluminum saturation index (ASI) of 0.8, the mass of the above components is 7.000 g, 0.933 g, 0.953 g, 1.244 g, and 0.019 g, respectively; in a pure silicate melt raw material with an aluminum saturation index (ASI) of 1.0, the mass of the above components is 7.000 g, 1.166 g, 0.794 g, 1.036 g, and 0.019 g, respectively; and in a pure silicate melt raw material with an aluminum saturation index (ASI) of 1.2, the mass of the above components is 7.000 g, 1.816 g, 0.514 g, 0.67 g, and 0.019 g, respectively.
[0025] In a fluorinated silicate melt raw material with an aluminum saturation index (ASI) of 1.0, the masses of SiO2, Al(OH)3, Na2CO3, K2CO3, Ba(NO3)2, and NaF are 7.000 g, 1.656 g, 0.082 g, 0.738 g, 0.019 g, and 0.443 g, respectively. In a fluorinated silicate melt raw material with an aluminum saturation index (ASI) of 1.0, the masses of SiO2, Al(OH)3, Na2CO3, K2CO3, Ba(NO3)2, and Na2SO4 are 7.000 g, 1.660 g, 0.075 g, 0.732 g, 0.019 g, and 0.880 g, respectively.
[0026] Table 1
[0027] S2: High-temperature and high-pressure experiments were conducted on three systems: fluid-pure silicate melt, fluid-fluorinated silicate melt, and fluid-sulfur-containing silicate melt. Initial fluid and initial solid phase, in a mass ratio of approximately 1:1, were sealed in gold sample tubes, weighed, and then placed in a quenched and cold-sealed autoclave. Fluid-melt isotope exchange reactions were carried out under set temperature and pressure. During the experiment, NiCr-Ni (K-type) thermocouples were used to measure the reaction temperature, and pressure sensors were used to monitor the reaction pressure. The uncertainty in temperature was within 5°C, and the uncertainty in pressure was within 30 bar. Oxygen fugacity was not specifically controlled, but because the autoclave material was a nickel-based alloy, the oxygen fugacity of the system after reaction with water under high-temperature and high-pressure conditions was approximately 0.5-1 log units higher than the Ni-NiO oxygen fugacity buffer pair. The high-temperature and high-pressure experiments could be run at 700-900°C and 2 kbar for 1 to 40 days. The experimental conditions for the isotope exchange reaction in this embodiment are shown in Table 1.
[0028] Groups 1-3 were time-series experiments, and the results showed that after 10 days of exchange reaction at 800℃, the fluid and melt phases reached elemental distribution and isotopic fractionation equilibrium. Groups 3-5 were temperature-based experiments; groups 1, 6, and 7 were experiments with different fluid concentrations; groups 1, 8, and 9 were experiments with different initial solid phase conditions (ASIs); and groups 1, 10, and 11 were experiments with three different silicate melt composition conditions: pure silicate melt, fluorinated silicate melt, and sulfur-containing silicate melt. After the fluid-melt isotopic exchange reaction, the gold sample tube was rapidly dropped into a water-cooling zone within 2 seconds using an external magnet to complete the quenching. The outer wall of the quenched gold sample tube was cleaned, dried, and weighed again to check for leakage during the experiment. Product extraction was performed on gold sample tubes with no significant weight change. The extraction process begins by immersing the gold sample tube in liquid nitrogen to freeze the fluid. After a few minutes, a small hole is cut in the tube, and once it returns to room temperature, the solution is slowly aspirated using a micropipette. The tube is then rinsed three times with deionized water at 78-82°C. The rinsing solution is collected together with the previously aspirated solution as the experimental fluid phase. The cleaned gold sample tube is dried and weighed again; the difference between the two weights is the weight of the extracted fluid. Finally, the gold sample tube is completely cut open, and the remaining solid is collected as the experimental melt phase. This combination of liquid nitrogen freezing separation technology and multi-step deionized water washing achieves efficient separation of the fluid and melt phases, with no significant cross-contamination during the separation process and a sample recovery rate of ≥95%.
[0029] S3: After evaporating the experimental fluid phase to dryness, dissolve it in acid to prepare a fluid phase solution. Take a portion of the solution and determine the Ba element content using inductively coupled plasma mass spectrometry. A portion of the experimental melt phase was used to make a target with epoxy resin. After grinding and polishing, the Ba element content was determined by laser ablation inductively coupled plasma mass spectrometry. The other portion was crushed, washed with deionized water and dried, and then dissolved in acid to prepare a melt phase solution. Ba was purified from the residual fluid phase solution and the melt phase solution using cation exchange resin, and Ba was separated from other matrix elements to obtain a first pure metal element solution from the residual fluid phase solution and a second pure metal element solution from the melt phase solution. The mass fractionation caused by multi-receiver inductively coupled plasma mass spectrometry was corrected by using a double diluent method, and the Ba isotope composition of the first and second pure metal element solutions was determined.
[0030] Divide the measured Ba concentration in the fluid phase solution by the Ba concentration in the experimental melt phase to obtain the Ba partition coefficient between the experimental fluid and melt phases. Then, calculate the δ0 values for the first and second pure metal element solutions. 138 / 134 Subtracting the Ba values yields the Ba isotope fractionation values between the experimental fluid phase and the experimental melt phase.
[0031] In summary, this application utilizes a dual verification system where elemental content / isotopic composition stabilizes over time to ensure isotopic exchange equilibrium between the fluid and silicate systems during experiments. By combining liquid nitrogen freezing separation technology with multi-step deionized water washing, efficient separation of the fluid and melt phases is achieved, with a sample recovery rate ≥95%. Through multi-step chemical purification and separation, and Ba isotopic composition determination using a double diluent method on a multi-receiver inductively coupled plasma mass spectrometer, the standard sample's δ¹⁸O₅... 138 / 134 Ba's long-term accuracy is better than ±0.05‰ (2SD).
[0032] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt, characterized in that, include: Prepare a salt solution as the initial fluid; The silicate melt with added metal elements was used as the initial solid phase; The initial fluid and initial solid phase are welded and sealed in a sample tube, which is then placed in a quenched and cold-sealed autoclave for isotope exchange reaction. The reaction is carried out for 1-40 days at a temperature of 700-900℃ and a pressure of 1.8-2.2kbar. The sample tube after the reaction was quenched and frozen in sequence and then restored to room temperature. The sample tube was opened and the solution inside was taken out. The inside of the sample tube was washed with deionized water to obtain a cleaning solution. The cleaning solution was mixed with the taken-out solution as the experimental fluid phase. The remaining solid in the sample tube was collected as the experimental melt phase. The metal element content and stable isotope composition of the experimental fluid phase and the experimental melt phase are determined, and the metal element partition coefficient and its isotope fractionation value between the experimental fluid phase and the experimental melt phase are calculated.
2. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 1, characterized in that, The molar ratio of NaCl to KCl in the salt solution is (0.5-1.5):(0.5-1.5), and the total concentration of Na and K in the salt solution is 0.5-1.5 mol / L.
3. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 1, characterized in that, The metallic elements include Ba, Sr, and Mg.
4. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 1, characterized in that, The silicate melt includes at least one of pure silicate melt, fluorinated silicate melt, and sulfur-containing silicate melt.
5. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 4, characterized in that, The pure silicate melt with added metal elements is prepared by grinding and mixing analytical grade SiO2, Al(OH)3, Na2CO3, K2CO3 and the corresponding nitrates of the metal elements, heating to decarburize, and melting and quenching, with an aluminum saturation index of 0.8-1.
2. The fluorinated silicate melt with added metal elements is prepared by grinding and mixing analytically pure SiO2, Al(OH)3, Na2CO3, K2CO3 and the corresponding nitrates of the metal elements, heating and decarburizing, melting and quenching, and then mixing in NaF. The aluminum saturation index is 0.8-1.
2. The sulfur-containing silicate melt with added metal elements is prepared by grinding and mixing analytically pure SiO2, Al(OH)3, Na2CO3, K2CO3 and the corresponding nitrates of the metal elements, heating and decarburizing, melting and quenching, and then mixing in Na2SO4. The aluminum saturation index is 0.8-1.
2.
6. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 1, characterized in that, The process of sealing the initial fluid and initial solid phase in a sample tube and then loading it into a cold-sealed autoclave for isotope exchange reaction includes: Monitor the temperature and pressure during the isotope exchange reaction process, controlling the temperature uncertainty to within 5℃ and the pressure uncertainty to within 30 bar.
7. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 1, characterized in that, By measuring the metal element content and stable metal isotope composition of the experimental fluid phase and the experimental melt phase at different isotope exchange reaction times, it is determined whether the isotope exchange reaction has reached element / isotope exchange equilibrium, and the isotope exchange reaction time is optimized.
8. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 1, characterized in that, The determination of the metal element content and stable metal isotope composition of the experimental fluid phase and the experimental melt phase includes: The experimental fluid phase was evaporated to dryness and then dissolved in acid to prepare a fluid phase solution. A portion of the solution was taken out and the metal element content was determined by inductively coupled plasma mass spectrometry. A portion of the experimental melt phase was used to make a target with epoxy resin. After grinding and polishing, the metal element content was determined by laser ablation inductively coupled plasma mass spectrometry. The other portion was crushed, washed with deionized water and dried, and then dissolved in acid to prepare a melt phase solution. The metal elements in the remaining fluid phase solution and the melt phase solution are separated from other matrix elements using a cation exchange resin to obtain a first pure metal element solution in the remaining fluid phase solution and a second pure metal element solution in the melt phase solution. The stable isotopic composition of the first and second pure metal solutions was determined by multi-receiver inductively coupled plasma mass spectrometry.
9. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 8, characterized in that, The mass fractionation caused by multi-receiver inductively coupled plasma mass spectrometry was corrected using a double diluent method.
10. The method for determining the elemental partition coefficient and isotopic fractionation value between a fluid and a melt according to claim 8, characterized in that, The calculation of the metal element partition coefficients and isotopic fractionation values between the experimental fluid phase and the experimental melt phase includes: Divide the measured concentration of metal elements in the fluid phase solution by the concentration of metal elements in the experimental melt phase to obtain the metal element partition coefficient between the experimental fluid phase and the experimental melt phase. The isotopic fractionation values between the experimental fluid phase and the experimental melt phase are obtained by subtracting the measured values of the stable metal isotopic composition of the first and second pure metal solutions.