Synthetic standard sample suitable for in-situ pyrrhotite Fe-S isotope analysis and preparation method and application thereof

Abstract

The invention relates to a synthetic standard sample suitable for in-situ pyrrhotite Fe-S isotope analysis and a preparation method and application thereof, and belongs to the technical field of geological analysis and material analysis. The particle size of the synthesized standard sample is 100-150 microns, and the interior of the particle is compact and free of holes; delta 34S is equal to-1.16 + / -0.22 per mill, and delta 56Fe is equal to 0.39 + / -0.03 per mill; the delta 34S in the synthesized standard sample is detected by SIMS, and the standard deviation 2SD of the delta 34S is 0.53%. The delta 56Fe in the synthesized standard sample is detected by LA-MC-ICPMS, and the standard deviation 2SD of the delta 56Fe is equal to 0.47 per mill. The method has the advantages that the pyrrhotite is synthesized in a laboratory, the reproducibility of the synthesized standard sample is realized, and the problems that the original in-situ pyrrhotite Fe-S isotope standard sample is natural in source, very few in available quantity and non-reproducible are solved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of geological analysis and material analysis, and particularly relates to a synthetic standard sample suitable for in-situ Fe-S isotope analysis of pyrrhotite, a preparation method thereof, and an application thereof. Background Art

[0002] Sulfides are common minerals formed during various processes such as magmatic activity, hydrothermal activity, and chemical sedimentation. The Fe-S isotope geochemistry of sulfides has now become a powerful tool for studying various geological processes, including magmatic, metamorphic, sedimentary, and biological processes. Pyrrhotite (Fe 1-x S, 0 ≤ x ≤ 0.125) is the most common iron sulfide in magmatic deposits and meteorites. The Fe-S isotope characteristics in pyrrhotite help to trace the sources of Fe and S in magmatic deposits, the formation, evolution, and ore-forming material sources of magmatic sulfides.

[0003] Traditionally, the method of solution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is often used to measure the Fe isotope composition of pyrrhotite, and the analysis precision (2SD) is better than 0.03‰; the S isotope composition of pyrrhotite is measured by isotope ratio gas mass spectrometry (IRMS), and the analysis precision (2SD) is better than 0.20‰. Although the above analysis techniques have high precision, there are problems of complex sample preparation and time consumption. In addition, pyrrhotite usually forms a complex symbiotic structure with other sulfides, such as the lodestone structure in Cu-Ni sulfide deposits. Therefore, the Fe-S isotope results of pyrrhotite obtained by traditional bulk analysis methods may be mixed values of Fe-S isotopes of multiple generations of pyrrhotite. With the development of modern test and analysis techniques, in-situ laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) and secondary ion mass spectrometry (SIMS) have greatly improved the spatial resolution of analysis and can accurately determine the Fe-S isotope composition of different regions at the micron scale of single-grain pyrrhotite. However, LA-MC-ICPMS and SIMS still have inherent instrumental fractionation and matrix effect problems, which limit the accurate determination of Fe-S isotope ratios. The previous research results have proved that using matrix-matched standard samples can effectively eliminate the matrix effect and instrumental fractionation generated during the analysis process.

[0004] Internationally reported natural pyrrhotite S isotope analysis reference materials include Po-10 (Reference 1: Gilbert, S. E., Danyushevsky, L. V., Rodemann, T., Shimizu, N., Gurenko, A., Meffre, S., Thomas, H., Large, R. R., and Death, D., 2014, Optimisation of laser parameters for the analysis of sulphur isotopes in sulphide minerals by laser ablation ICP-MS: Journal of Analytical Atomic Spectrometry, v. 29, no. 6, p. 1042-1051.), Alexo (Reference 2: LaFlamme, C., Martin, L., Jeon, H., Reddy, S. M., Selvaraja, V., Caruso, S., Bui, T. H., Roberts, M. P., Voute, F., Hagemann, S., Wacey, D., Littman, S., Wing, B., Fiorentini, M., and Kilburn, M. R., 2016, In situ multiple sulfur isotope analysis by SIMS of pyrite, chalcopyrite, pyrrhotite, and pentlandite to refine magmatic ore genetic models: Chemical Geology, v. 444, p. 1-15.), YP136 (Reference 3: Li, R., Xia, X., Yang, S., Chen, H., and Yang, Q., 2019, Off-Mount Calibration and One New Potential Pyrrhotite Reference Material for Sulfur Isotope Measurement by Secondary Ion Mass Spectrometry: Geostandards and Geoanalytical Research, v. 43, no.1, p. 177-187.) and JC-Po (Reference 4: Chen, L., Liu, Y., Li, Y., Li, QL, and Li, XH, 2021, New potential pyrrhotite and pentlandite reference materials for sulfur and iron isotope microanalysis: Journal of AnalyticalAtomic Spectrometry, v. 36, no. 7, p. 1431-1440.), and its Fe isotope analysis standards include JC-Po (Reference 4: Chen et al., 2021) and Ll-Po (Reference 5: Feng, Y., Zhang, W., Hu, Z., Luo, T., Li, Q., and Liu, J., 2024, New Potential Sulfide Reference Materials forMicrobeam S-Fe-Cu Isotope Measurements: Geostandards and GeoanalyticalResearch, v. 48, no. 1, p. 227-244.). The only pyrrhotite Fe-S isotope standard reported internationally that can simultaneously test pyrrhotite is JC-Po (Reference 4: Chen et al., 2021). Obviously, the available amount of natural pyrrhotite Fe-S isotope analysis standard is very small and non-renewable, which is difficult to meet the growing needs of existing micro-area in-situ analysis instruments for pyrrhotite Fe-S isotope composition analysis. Therefore, it is urgent to develop sufficient and renewable pyrrhotite standards. .

[0005] Therefore, this method will provide a reproducible and sufficient synthetic standard suitable for in situ pyrrhotite Fe-S isotope analysis to meet the needs of existing micro-area in situ analysis such as LA-MC-ICPMS and SIMS. Summary of the invention

[0006] Since the in-situ pyrrhotite Fe-S isotope standards in the past were all from natural sources, the available quantity was very small and non-renewable, which made it difficult to meet the needs of today's high-resolution instrument testing process. This application can synthesize pyrrhotite in the laboratory, achieve the regeneration of the synthetic standard, and then use multi-collector inductively coupled plasma mass spectrometry to determine the δ 56 Fe value determination and isotope ratio gas mass spectrometry determination of δ 34The S value is determined, and then a large number of in-situ Fe-S isotope analyses are carried out on synthetic pyrrhotite to determine the homogeneity of the synthetic pyrrhotite standard sample. This synthetic substance is a potential standard sample for in-situ pyrrhotite Fe-S isotope analysis in the latest artificial synthesis in this field.

[0007] Currently, the commonly used methods for in-situ sulfur isotope analysis of pyrrhotite are mainly ion probe (SIMS) and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS). The beam spot diameter of SIMS is generally 25 μm, and that of LA-MC-ICPMS is generally 35 μm (Literature 6: Chen Lei, Li Xianhua, Li Jianwei, Li Qiuli, and Liu Yu, 2019, In-situ sulfur isotope analysis technology of pyrite microarea by ion probe and research on ore deposit genesis: The 9th National Academic Symposium on Metallogeny Theory and Prospecting Methods, Nanjing, Jiangsu, China, 2019, p. 1); while the beam spot diameter of LA-MC-ICPMS for Fe isotope of pyrrhotite is generally above 35 μm (Literature 4: Chen et al., 2021). At the same time, when testing the homogeneity of the pyrrhotite standard sample, two points need to be selected on the same particle, so it is necessary to ensure that the particle size of the synthetic pyrrhotite is at least above 100 μm.

[0008] The first object of the present invention is to disclose a synthetic standard sample suitable for in-situ pyrrhotite Fe-S isotope analysis.

[0009] The second object of the present invention is to disclose a preparation method of the above synthetic standard sample.

[0010] The third object of the present invention is to disclose the application of the above synthetic standard sample.

[0011] The object of the present invention is achieved by the following technical solutions: A synthetic standard sample suitable for in-situ pyrrhotite Fe-S isotope analysis, characterized in that: the particle size of the synthetic standard sample is 100 μm - 150 μm, the interior of the particle is dense and has no holes; its δ 34 S = -1.16 ± 0.22‰, δ 56 Fe = 0.39 ± 0.03‰; in the synthetic standard sample, δ 34 S is detected by SIMS, and the standard deviation 2SD of δ 34 S is 0.53‰. After being tested by the F test method, the F value is less than the F α value, and the F α value is obtained from the F distribution critical value table at a significance level α = 5%; in the synthetic standard sample, δ 56Fe was detected by LA-MC-ICPMS, δ 56 The standard deviation of Fe is 2SD = 0.47‰. F Testing method for testing, F Value less than F α value, F α When the significance level is α=5%, F The distribution critical value table is obtained; The synthetic standard was prepared by the following method: (1) Take FeSO4·7H2O and CH3CSNH2 and place them in volumetric flasks to prepare FeSO4·7H2O solution and CH3CSNH2 solution respectively, and place them in a beaker. According to the amount of substance, Fe:S=1:3, and stir with a glass rod to mix thoroughly; (2) Take the reactor and add the solution mixed in the first step so that the solution occupies 60% of the volume of the reactor; (3) The temperature was controlled at 200°C and heated for 24 hours; (4) After heating, the reactants in the reactor were taken out, cooled and filtered to obtain a gray-black solid; (5) The gray-black solid part was washed three times with alcohol in an ultrasonic cleaner by repeated shaking, and naturally dried. Particles with a particle size of 100 μm-150 μm were selected as synthetic standards.

[0012] The method for preparing the synthetic standard sample described in the above technical solution comprises the following steps: (1) Take FeSO4·7H2O and CH3CSNH2 and place them in volumetric flasks to prepare FeSO4·7H2O solution and CH3CSNH2 solution respectively, and place them in a beaker. According to the amount of substance, Fe:S=1:3, and stir with a glass rod to mix thoroughly; (2) Take the reactor and add the solution mixed in the first step so that the solution occupies 60% of the volume of the reactor; (3) The temperature was controlled at 200°C and heated for 24 hours; (4) After heating, the reactants in the reactor were taken out, cooled and filtered to obtain a gray-black solid; (5) The gray-black solid part was washed three times with alcohol in an ultrasonic cleaner by repeated shaking, and naturally dried. Particles with a particle size of 100 μm-150 μm were selected as synthetic standards.

[0013] Application of the synthetic standard sample described in the above technical solution in in-situ pyrrhotite Fe-S isotope analysis.

[0014] The present invention has the following beneficial effects: 1. The technical solution of the present invention can synthesize pyrrhotite in the laboratory, realizing the regeneration of synthetic reference samples, and solving the problem that the previous in-situ pyrrhotite Fe-S isotope reference samples were all of natural origin, with very few available quantities, non-renewable, and difficult to meet the requirements of current high-resolution instrument testing processes.

[0015] 2. For the synthetic reference sample (synthetic pyrrhotite) suitable for in-situ pyrrhotite Fe-S isotope analysis prepared by the present invention, first use the multi-collector inductively coupled plasma mass spectrometry solution method to determine the δ 56 Fe value of the synthetic pyrrhotite, and use the isotope ratio gas mass spectrometry method to determine the δ 34 S value of the synthetic pyrrhotite. Then, conduct a large number of in-situ Fe-S isotope analyses on the synthetic pyrrhotite to determine the homogeneity of the synthetic pyrrhotite reference sample. This synthetic substance is a potential reference sample for the latest artificial synthesis of in-situ pyrrhotite Fe-S isotope analysis in this field. Description of the Drawings

[0016] Figure 1 It is the resin target sample effect diagram of the synthetic reference sample (synthetic pyrrhotite) particles in Example 1; Figure 2 It is the product diagram of the resin target sample of the synthetic reference sample (synthetic pyrrhotite) particles in Example 1; Figure 3 It is the morphology and structure photo of the synthetic pyrrhotite taken by FESEM in Example 3; Figure 4 It is the iron isotope composition of the synthetic pyrrhotite measured by the solution method in Example 4; Figure 5 It is the sulfur isotope composition of the synthetic pyrrhotite measured by the isotope ratio mass spectrometry method in Example 5; Figure 6 It is the backscattered image of the synthetic pyrrhotite particles in Example 6; Figure 7 It is the sulfur isotope composition of the synthetic pyrrhotite measured by secondary ion mass spectrometry in Example 7; Figure 8 It is the iron isotope composition of the synthetic pyrrhotite measured by LA-MC-ICP-MS in Example 8. Detailed Embodiments

[0017] To facilitate the understanding of the technical solution of the present invention, the following further describes a synthetic reference sample suitable for in-situ pyrrhotite Fe-S isotope analysis, its preparation method and application of the present invention with specific examples.

[0018] Example 1: A synthetic reference sample (pyrrhotite particles) suitable for in-situ pyrrhotite Fe-S isotope analysis: 1. This patent synthesizes pyrrhotite samples by the hydrothermal method. The specific steps are as follows: (1) Take ferrous sulfate heptahydrate (FeSO4·7H2O) and thioacetamide (CH3CSNH2) and place them in volumetric flasks respectively to prepare FeSO4·7H2O solution and CH3CSNH2 solution. Put them in a beaker so that Fe:S = 1:3 (amount of substance), and stir with a glass rod to mix well. (2) Take a reaction kettle and add the mixed solution in the first step so that the solution accounts for 60% of the volume of the reaction kettle. (3) Control the temperature at 200 °C and heat for 24 h. (4) After heating, take out the reactants in the reaction kettle, cool and filter to obtain a grayish-black solid. (5) Wash the grayish-black solid part repeatedly in an ultrasonic cleaner with alcohol for 3 times, dry it naturally, and select particles with a particle size of 100 μm - 150 μm as the synthetic standard sample (hereinafter referred to as: synthetic pyrrhotite). The function of washing with alcohol in the ultrasonic cleaner is to shake off the fine pyrite particles adhering to the large particle synthetic pyrrhotite, retain the large particles, and the small particles can be suspended in the alcohol solution and poured out. Alcohol is volatile and can be quickly dried.

[0019] 2. The backscattered images of the synthetic pyrrhotite (synthetic standard sample) crystals prepared in step 1 taken by a field emission scanning electron microscope show that the particle size can reach 100 μm - 150 μm, and the interior of the particles is dense without pores, meeting the requirements of microbeam analysis, as Figure 6 shown.

[0020] 3. Select synthetic pyrrhotite crystal particles with a particle size of 100 μm - 150 μm and divide them into two parts. One part is synthetic pyrrhotite particle powder, and the other part is made into a resin target sample according to the method in step 4 below; 4. Select 30 - 40 synthetic standard sample (synthetic pyrrhotite) particles with a particle size of 100 - 150 μm, 10 - 15 natural pyrrhotite standard sample JC-Po with a particle size of 100 - 300 μm, and 7 - 10 pyrite standard sample Sonora with a particle size of 100 - 300 μm and embed them in a circular resin sheet with a diameter of about 2.5 cm and a thickness of 1 - 2 cm, so that the synthetic standard sample, natural pyrrhotite standard sample, and pyrite standard sample are all exposed on one side surface of the thin slice. The resin target sample effect diagram of the synthetic standard sample (synthetic pyrrhotite) particles is as Figure 1 shown, and the product diagram is as Figure 2 shown.

[0021] Example 2: Quantitative analysis of synthetic pyrrhotite using an electron probe: 2.1 Coating with conductive material: (1) Paste the synthetic pyrrhotite target sample prepared in Example 1 onto the sample stage with conductive glue, and then blow away impurities with an ear bulb. (2) Using a JEC-3000FC automatic vacuum coating instrument, coat a continuous carbon film on the surface of the target sample on the above sample stage. To ensure that the sample to be measured can conduct electricity and does not affect the observation of the sample, the thickness of the carbon film layer needs to be controlled within 10nm - 20nm. For example, it can be 10nm, or 15nm, etc.

[0022] 2.2 Use an electron probe to perform quantitative analysis on synthetic pyrrhotite: (1) Place the above carbon-coated sample stage into a JEOL JXA-8100 microprobe equipped with a full-automatic X-ray WDS ray. After evacuating, adjust its working distance to 15mm and adjust the focal length. (2) Switch the electron probe to the point analysis mode and sequentially select 40 points on the surface of the synthetic pyrrhotite. (3) Under the working conditions of an electron beam current of 20nA, an acceleration voltage of 15kV, and a beam diameter of 5μm, perform chemical composition analysis on the synthetic pyrrhotite. The average value of the Fe content is 60.21wt%, the average value of the S content is 39.51wt%, and the chemical formula is Fe 0.125 S, confirming that the synthetic sample is pyrrhotite and the chemical composition is uniform.

[0023] Example 3: Use a field emission scanning electron microscope to photograph the morphology and structure of synthetic pyrrhotite: 3.1 Sample preparation: (1) Directly sprinkle the synthetic pyrrhotite particle powder prepared in Example 1 on the double-sided carbon conductive glue of the sample stage, press it tightly with a glass plate, and then blow away the particles that are not firmly adhered with an ear bulb. (2) Using a JEC-3000FC automatic vacuum coating instrument, coat a continuous carbon film on the surface of the synthetic pyrrhotite particles on the above sample stage. To ensure that the sample to be measured can conduct electricity and does not affect the observation of the sample, the thickness of the carbon film layer needs to be controlled within 10nm - 20nm. For example, it can be 10nm, or 15nm, etc.

[0024] 3.2 Use a field emission scanning electron microscope to photograph the morphology and structure of synthetic pyrrhotite: (1) Place the sample in a Zeiss Supra 55 type field emission scanning electron microscope equipped with an Oxford X-act energy spectrometer. After evacuating, adjust its working distance to 15mm and adjust the focal length. (2) Locate the position of the synthesized pyrrhotite sample under FESEM. Under the conditions of an acceleration voltage of 20 kV, a magnification of 200 times, and both the input count rate and output count rate exceeding 10,000 cps, different mineral phases are distinguished by scanning the gray scale of the sample image. (3) Utilize the semi - quantitative elemental analysis function of the energy spectrometer to preliminarily determine that the found mineral is synthesized pyrrhotite. (4) Under the conditions of an electron beam current of 20 nA and a working distance of 12.3 mm, observe the morphological characteristics of the synthesized pyrrhotite at a magnification of 8000 times. The morphology is plate - shaped, as Figure 3 shown.

[0025] Example 4: Determine the iron isotope composition of synthesized pyrrhotite using the solution method: (1) Select 8 mg of the synthesized pyrrhotite particles prepared in Example 1 and place them in a beaker. (2) Purify iron using an anion resin (Bio - Rad AG1 - X8) under the condition of 6N HCl. The 6N HCl can remove matrix elements. (3) First, elute Fe with 0.4N HCl and H2O, and then with 6N HCl. (4) All mineral isolates need to be processed twice to finally obtain a high - purity iron solution. (5) Place the above - mentioned high - purity iron solution in a Thermo Fisher Scientific Neptune - Plus MC - ICP - MS instrument to determine the iron isotope composition of the synthesized pyrrhotite. (6) It needs to be repeatedly tested 3 times by the same experimenter in the same time period and the same laboratory using the same method. The results are as Figure 4 shown. The iron isotope composition of the synthesized pyrrhotite δ 56 Fe = 0.39 ± 0.03‰.

[0026] Example 5: Determine the sulfur isotope composition of synthesized pyrrhotite using isotope ratio mass spectrometry: (1) Combine 8 mg of the pyrrhotite sample prepared in Example 1 with Cu2O and grind it in an agate mortar. (2) Burn the sample under vacuum at 900 °C to produce SO2 gas. (3) Purify SO2 at low temperature and perform mass spectrometry analysis using the standard sample double - inlet scheme on a MAT 253 mass spectrometer to determine the sulfur isotope composition of the synthesized pyrrhotite. (4) It needs to be repeatedly tested 11 times by the same experimenter in the same time period and the same laboratory using the same method. The results are as Figure 5 shown. The sulfur isotope composition of the synthesized pyrrhotite δ 34 S = - 1.16 ± 0.22‰.

[0027] Example 6: Taking backscattered electron images (BSE) of synthetic pyrrhotite using a field emission scanning electron microscope: 6.1 Coating with a conductive material: (1) Paste the target sample prepared in Example 1 onto the sample stage with conductive glue, and then blow away impurities with an ear syringe; (2) Using a JEC-3000FC automatic vacuum coating instrument, coat the surface of the target sample on the above sample stage with a continuous carbon film. To ensure that the sample to be measured can conduct electricity and does not affect the observation of the sample, the thickness of the carbon film layer needs to be controlled within 10 nm - 20 nm. For example, it can be 10 nm or 15 nm, etc.

[0028] 6.2 Taking backscattered electron images (BSE) of synthetic pyrrhotite crystal grains using a field emission scanning electron microscope: (1) Place the above sample target into the sample chamber of a Zeiss Supra 55 field emission scanning electron microscope equipped with an Oxford X-act energy spectrometer. After evacuating, adjust its working distance to 15 mm and adjust the focal length; (2) Locate the position of synthetic pyrrhotite in the backscattered electron mode. Under the conditions of an acceleration voltage of 20 kV, a magnification of 200 times, and both the input count rate and output count rate exceeding 10,000 cps, distinguish different mineral phases by scanning the gray scale of the sample image; (3) Use the elemental semi-quantitative analysis function of the energy spectrometer to preliminarily determine that the found mineral is synthetic pyrrhotite; (4) Take a backscattered electron photo of synthetic pyrrhotite at a magnification of 760 times under the conditions of an electron beam current of 20 nA and a working distance of 5 mm. The backscattered electron photo is as Figure 6 shown. The crystal grain size of the synthetic sample is 100 μm - 150 μm, and the interior of the grains is dense without pores.

[0029] Example 7: Verifying the sulfur isotope homogeneity of synthetic pyrrhotite using secondary ion mass spectrometry: 7.1 Coating with a conductive material: (1) Paste the resin target sample prepared in step 4 of Example 1 onto the sample stage with conductive glue, and then blow away impurities with an ear syringe; (2) Using a JEC-3000FC automatic vacuum coating instrument, coat the surface of the target sample on the above sample stage with a continuous carbon film. To ensure that the sample to be measured can conduct electricity and does not affect the observation of the sample, the thickness of the carbon film layer needs to be controlled within 10 nm - 20 nm. For example, it can be 10 nm or 15 nm, etc.

[0030] 7.2 Testing the sulfur isotope composition of synthetic pyrrhotite in a secondary ion mass spectrometer: (1) Place the above sample target into the sample chamber of the secondary ion mass spectrometer. First, locate the position of synthetic pyrrhotite on the target and mark it as (X1, Y1), the position of JC-Po as (X2, Y2), and the position of Sonora as (X3, Y3). (2) Adopt the standard sample - sample - standard sample method (SSB) to sequentially select synthetic pyrrhotite particles and standard samples, and use the standard samples to verify the stability of the instrument. The results are as Figure 7 shown. The standard deviation of the δ 34 S value of the sample is 0.53‰ (2SD). Use the F test method for inspection, and prove that the δ 34 S value of synthetic pyrrhotite is uniform.

[0031] 7.3 Test method for the uniformity of sulfur isotope composition: According to the general principle of standard substance value determination in the National Metrology Technical Specification of the People's Republic of China, the test method for the uniformity of sulfur isotope composition in this patent adopts the one-way analysis of variance method. The specific content is as follows: (1) To evaluate the sample uniformity, it is necessary to extract m ( m ≥ 9) units from the overall unit of the standard substance, and select a measurement method that is not lower than the precision and sensitivity of the value determination method; (2) In this study, 15 synthetic pyrrhotite particles were randomly selected to determine the uniformity of the δ 34 S value of synthetic pyrrhotite, and two sub-samples were extracted from each particle, and each sub-sample was regarded as an independent sample; (3) Under the same conditions, obtain m groups ( m is 15) of equal-precision measurement steps as follows. In the following formulas, x the value is the sulfur isotope ratio measured in step 7.2, m represents the number of selected data groups, and n represents the number of data in each group: x 11 , x 12 , the average value ; x 21 , x 22 , the average value ; …………… x m1 , x m2 , the average value ; Let (1) (2) Sum of squares between groups (3) Sum of squares within groups (4) (5) (6) Variance between groups (7) Variance within groups (8) This method can be used to determine whether the data are of equal precision - namely F - test method; Use as a statistic F : (9) Therefore, this statistic is a v 1, v 2) F distribution variable.

[0032] According to the degrees of freedom ( v 1, v 2) and the given significance level α (α = 5%), from the F distribution critical value table, we obtain F α value. The F value calculated in this study is 1.00, which is much smaller than F α (2.42), indicating that this synthetic reference sample can be used as a reference sample for micro-area in-situ analysis methods.

[0033] Example 8: Use LA-MC-ICPMS to verify the iron isotope homogeneity of synthetic pyrrhotite: 8.1 Clean the sample: (1) First, polish the surface of the resin target sample prepared in step 4 of Example 1 with 0.25um polishing paste; (2) Clean the surface of the sample with clean water; (3) Place the sample in a beaker filled with alcohol and ultrasonically clean the sample for three minutes using an ultrasonic instrument; (4) Air dry naturally.

[0034] 8.2 Test the iron isotope composition of synthetic pyrrhotite in LA-MC-ICPMS: (1) Place the above sample target into the sample chamber of a laser ablation multiple collector inductively coupled plasma mass spectrometer. First, locate the position of synthetic pyrrhotite on the target and mark it as (X1, Y1), the position of JC-Po as (X2, Y2), and the position of Sonora as (X3, Y3). (2) Under the conditions of an ablation pit diameter of 20 μm, an ablation time of 10 s, a repetition frequency of 6 Hz, and a laser beam energy density of 2 J / cm 2 , the synthetic pyrrhotite particles and the standard sample were sequentially selected using the standard sample-sample-standard sample method (SSB). The stability of the instrument was verified using the standard sample, and the standard deviation of the δ 56 Fe value of the sample was 0.47‰ (2SD). The F test method was used for inspection, proving that the δ 56 Fe value of the synthetic pyrrhotite was uniform.

[0035] 8.3 Test method for the homogeneity of iron isotope composition: According to the general principle of standard material value determination in the "National Metrology Technical Specification of the People's Republic of China", the homogeneity test method for the iron isotope composition of this patent adopts the one-way analysis of variance method, and the specific content is as follows: (1) To evaluate the sample homogeneity, it is necessary to extract m ( m ≥ 9) units from the overall unit of the standard material, and select a measurement method that is not lower than the precision and sensitivity of the value determination method; (2) In this study, 15 pyrrhotite particles were randomly selected to determine the homogeneity of the iron isotope ratio of synthetic pyrrhotite, and two sub-samples were extracted from each particle, and each sub-sample was regarded as an independent sample; (3) The m groups ( m is 15) of equal-precision measurement steps are as follows. In the following formula, x is the iron isotope ratio measured in step 8.2, m represents the number of selected data groups, and n represents the number of data in each group: x 11 , x 12 , average value ; x 21 , x 22 , average value ; …………… x m1 , x m2 , average value ; Let (10) (11) Sum of squares of differences between groups (12) Sum of squares of differences within groups (13) (14) (15) Variance between groups (16) Variance within groups (17) This method can be used to determine whether the data has equal precision - that is F - test method; Take as the statistic F : (18) Therefore, this statistic is a v 1, v 2) F distribution variable.

[0036] According to the degrees of freedom ( v 1, v 2) and the given significance level α (α = 5%), from the F distribution critical value table, we find F α value. The F value calculated in this study is 1.51, which is much smaller than F α (2.42), indicating that this synthetic standard sample can be used as the standard sample for the micro-area in-situ analysis method.

[0037] Example 9: Expression of Fe-S isotope composition of synthetic pyrrhotite: 9.1 34 S / 32 The S / S ratio uses the composition of Vienna-Cañon Diablo troilite (V-CDT) as the standard, and the formula is as follows: δ 34 S 测试值 = ( 34 S / 32 S 测试值 ÷ 0.044163 - 1) × 1000 (19) 9.2 56 Fe / 54 The Fe / Fe ratio uses the composition of IRMM-014 as the standard, and the formula is as follows: δ 56Fe 测试值 = ( 56 Fe / 54 Fe 测试值 ÷ 15.6929 - 1) × 1000 (20) The Fe-S isotope composition of synthetic pyrrhotite is well uniform. As Figure 7 and Figure 8 shown, the δ 56 Fe value of synthetic pyrrhotite is 0.39 ± 0.03‰ and the δ 34 S value is -1.16 ± 0.22‰, which is suitable as a standard sample for micro-area in-situ analysis methods.

[0038] Due to the extremely small quantity and non-renewability of available natural pyrrhotite Fe-S isotope standard samples for micro-area in-situ analysis in the past, it is difficult to meet the requirements of standard samples in the current in-situ geochemical analysis process. In this application, through a large number of analytical experiments on synthetic pyrrhotite, it has been proven that synthetic pyrrhotite has good uniformity and is suitable as a standard sample for micro-area in-situ pyrrhotite Fe-S isotope analysis, which can meet the shortage of existing pyrrhotite standard samples in the instrument analysis process. Moreover, synthetic pyrrhotite has repeatability, can ensure highly uniform composition, stable physical and chemical properties, low cost, high production rate, is relatively convenient to obtain, and does not require spending time on field sampling. This synthetic substance is a potential standard sample for the latest pyrrhotite Fe-S isotope analysis in this field.

[0039] The above is only a preferred embodiment of the present invention, and it does not impose any form and substantial limitations on the present invention. Those skilled in the art, within the scope of the technical solution of the present invention, when making some minor changes, modifications and equivalent variations of evolution using the technical content disclosed above, are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the substantial technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A synthetic standard sample applicable to in-situ pyrrhotite Fe-S isotope analysis, characterized in that: The particle size of the synthesized reference sample is 100 μm - 150 μm, and the interior of the particles is dense and pore-free; its δ 34 S = -1.16 ± 0.22‰, δ 56 Fe = 0.39 ± 0.03‰; In the synthesized reference sample, δ 34 S is detected by SIMS, and the standard deviation 2SD of δ 34 S is 0.53‰. After being tested by the F test method, the F value is less than the F α value. The F α value is obtained from the F distribution critical value table at a significance level of α = 5%; In the synthesized reference sample, δ 56 Fe is detected by LA-MC-ICPMS, and the standard deviation 2SD of δ 56 Fe is 0.47‰. After being tested by the F test method, the F value is less than the F α value. The F α value is obtained from the F distribution critical value table at a significance level of α = 5%; The synthetic reference sample is prepared by the following method: (1) Take FeSO4·7H2O and CH3CSNH2 and place them in volumetric flasks respectively to prepare FeSO4·7H2O solution and CH3CSNH2 solution. Place them in a beaker, and make the molar ratio of Fe:S = 1:

3. Stir with a glass rod to mix well; (2) Take a reaction kettle and add the mixed solution in the first step to make the solution account for 60% of the volume of the reaction kettle; (3) Control the temperature at 200 °C and heat for 24 h; (4) After heating, take out the reactants in the reaction kettle, cool and filter to obtain a grayish-black solid; (5) Wash the grayish-black solid part in an ultrasonic cleaner with alcohol by shaking repeatedly for 3 times, dry it naturally, and select particles with a particle size of 100 μm - 150 μm as the synthetic reference sample.

2. The preparation method of the synthetic reference sample according to claim 1, comprising the following steps: (1) Take FeSO4·7H2O and CH3CSNH2 and place them in volumetric flasks respectively to prepare FeSO4·7H2O solution and CH3CSNH2 solution. Place them in a beaker, and make the molar ratio of Fe:S = 1:

3. Stir with a glass rod to mix well; (2) Take a reaction kettle and add the mixed solution in the first step to make the solution account for 60% of the volume of the reaction kettle; (3) Control the temperature at 200 °C and heat for 24 h; (4) After heating, take out the reactants in the reaction kettle, cool and filter to obtain a grayish-black solid; (5) Wash the grayish-black solid part in an ultrasonic cleaner with alcohol by shaking repeatedly for 3 times, dry it naturally, and select particles with a particle size of 100 μm - 150 μm as the synthetic reference sample.

3. The application of the synthetic reference sample according to claim 1 in in-situ pyrrhotite Fe-S isotope analysis.

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