A method for in-situ microscale determination of silver isotopes in silver gold ore samples

Abstract

This invention belongs to the field of solid sample isotope analysis technology, specifically relating to a method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area. This application proposes a method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area. By correcting the silver isotope ratio of the sample using standard materials, the silver content of the sample can be obtained. This method is simple, efficient, and easy to operate. It can identify the silver isotope composition characteristics within mineral particles, reflect isotope changes at the microscale, and has the advantage of high spatial resolution (12-30 μm). This method uses silver-gold ore samples as an example only, but it can also be extended to archaeological samples, environmental samples, and biological materials. Simultaneously, it solves the problem of the scarcity of natural matrix-matched standard materials, allowing for the preparation of standard materials with different silver contents to analyze silver-gold ore samples with varying silver contents.

Description

Technical Field

[0001] This invention belongs to the field of solid sample isotope analysis technology, specifically relating to a method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area. Background Technology

[0002] Existing silver isotope analysis methods are mainly divided into bulk analysis methods, also known as solution nebulization-multiple-collector inductively coupled plasma mass spectrometry (SN-MC-ICP-MS). The specific steps involve chemically digesting the sample, followed by column chromatography to purify the target element Ag, and finally using a multiple-collector inductively coupled plasma mass spectrometer for isotope analysis. The entire process is cumbersome and complex, often taking a week or more from sample preparation to data acquisition, significantly reducing analytical efficiency and making data acquisition time-consuming and tedious. Furthermore, the sample digestion and chromatographic separation processes are quite complex, requiring operators with high levels of expertise, making silver isotope analysis a high-barrier-to-entry method. On the other hand, these bulk analysis methods only provide mixed information and cannot effectively identify differences in isotopic composition at the microscopic scale of the sample. However, in-situ silver isotope analysis methods in micro-areas are currently lacking. To improve analytical efficiency and identify the microscale (~10 μm) silver isotope composition characteristics of silver-gold ore samples, this invention provides a micro-area in-situ silver isotope analysis method based on fsLA-MC-ICP-MS.

[0003] In laser ablation mass spectrometry (LAMS), matrix effects, mass discrimination effects, and instrument drift are several major factors affecting analytical accuracy. In practical analytical testing, the standard-sample interpolation (SSB) method is typically used to correct for mass bias and matrix effects; standard materials are the cornerstone of micro-area analysis. Minerals of the same species with similar physical properties and chemical compositions are the preferred choice for calibration standards. However, natural silver-gold mines with uniform silver isotope compositions and varying silver contents are extremely rare, and no publicly available silver isotope standards for silver-gold mines have been published. This severely hinders the promotion and application of in-situ silver isotope analysis of silver-gold mines in micro-areas. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention aims to provide a method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area, providing technical support for deep mineral exploration (especially gold and silver ore) and solving the problem of scarce standard materials.

[0005] The technical solution of this application discloses a method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area, comprising the following steps:

[0006] S1. After mixing silver powder and gold powder in a known proportion, the mixture is sintered and quenched to obtain a solid silver-gold standard sample.

[0007] S2. Cut the test sample and the solid silver-gold standard sample into fine particles with a diameter ≤1cm, cure them with epoxy resin and polish them to obtain the sample targets of the test sample and the standard sample.

[0008] S3. The sample targets of the test sample and the standard sample are ablated using laser to generate sample aerosol particles;

[0009] S4. After determining the homogeneity of the isotopic composition of the standard sample by random in-situ analysis, micro-copper-solution analysis was performed to obtain the silver isotope determination results, which were used as reference values ​​for the standard material.

[0010] S5. Subsequently, the standard sample and the sample target of the test sample were analyzed sequentially on the aerosol particles using a multi-receiver inductively coupled plasma mass spectrometer in the order of standard sample-test sample-standard sample. 109 Ag and 107 Ag, respectively, to obtain the silver isotope ratio of the standard sample target and the silver isotope ratio of the sample to be tested before the sample to be tested and after the sample to be tested.

[0011] S6. Correct the silver isotope ratio of the test sample using the silver isotope ratio of the target sample of the standard sample before and after the test sample analysis, and obtain the silver isotope ratio of the test sample relative to the reference value of the standard material mentioned in S3. Convert it to the value relative to the international standard NIST 978a, which is the silver isotope value of the test sample.

[0012] Furthermore, the silver powder and gold powder mentioned in S1 are both nanospheres with a particle size distribution of 100-400 nm.

[0013] Furthermore, the known proportions of silver powder and gold powder composition are such that the mass of silver powder accounts for 2%, 5%, or 10% of the mass of the silver powder and gold powder mixture.

[0014] Furthermore, the sintering temperature is 1064-1100℃, and the temperature is maintained for 3 minutes after reaching the melting point of the gold powder.

[0015] Furthermore, the laser ablation described in S3 is femtosecond laser ablation, and the ratio of silver isotope signal intensity between the test sample and the standard sample is adjusted by adjusting the laser ablation parameter intensity to ensure that the deviation is ≤20%.

[0016] Furthermore, in step S5, the following formula is used for correction:

[0017]

[0018] Where, δ 109 Ag represents the silver isotope ratio of the sample to the reference value of the standard substance;

[0019] 109 Ag / 107 Agsam represents the sample to be tested. 109 Ag / 107 The value of Ag;

[0020] 109 Ag / 107 Ag std-A This indicates the standard sample target for analysis before the sample to be tested. 109 Ag / 107 The value of Ag;

[0021] 109 Ag / 107 Ag std-A This indicates the standard sample target for analysis after the sample to be tested. 109 Ag / 107 The value of Ag.

[0022] Furthermore, the transformation described in S6 is performed according to the following formula:

[0023] δ 109 Ag NIST978a =δ 109 Ag std-NIST978a +δ 109 Ag sam-std ;

[0024] Where, δ 109 Ag std-NIST978a This indicates the value of the sample relative to the international Ag isotope standard NIST SRM 978a; δ 109 Ag sam-std This indicates the sample's value relative to the reference standard described in S4; δ 109 Ag NIST978a This indicates the value of the silver isotope in the sample to be tested.

[0025] Beneficial effects: 1. A micro-area in-situ method for determining silver isotopes in silver-gold ore samples is proposed, greatly improving analytical efficiency, saving time, and reducing costs. Furthermore, the method provided by this invention can identify the silver isotopic composition characteristics within mineral grains, reflecting isotopic changes at the microscale and possessing the advantage of high spatial resolution (12-30 μm). This method is only used as an example of silver-gold ore samples; it can also be extended to archaeological samples, environmental samples, and biological materials.

[0026] 2. The proposed method for preparing silver-gold ore standard materials is simple, efficient, and easy to operate. The silver isotope composition is uniform, and the physicochemical properties are similar to those of natural minerals. It solves the problem of the scarcity of natural matrix-matching standard materials and can prepare standard materials with different silver contents according to needs to analyze silver-gold ore samples with different silver contents. Attached Figure Description

[0027] Figure 1 This is an example of the analytical process, i.e., the standard substance preparation process, of the present invention;

[0028] Figure 2 This invention demonstrates the uniformity of the synthesized standard substances and the solution determination.

[0029] Figure 3 This invention provides the results of analyzing the silver isotope composition of natural samples. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0032] Unless otherwise specified, the technical terms in this specification have the same meaning as those generally understood by those skilled in the art; however, in case of any conflict, the definitions in this specification shall prevail.

[0033] The term "silver-gold ore" as used in this application refers to minerals primarily composed of gold, silver, and other trace elements. While classified as silver-gold ore or gold-silver ore due to differences in silver content, their essence remains largely the same. For ease of description, this invention will uniformly refer to them as silver-gold ore. In nature, silver-gold ore is mostly found in silver and gold mineralization belts. In mineralogy, silver isotopes are an emerging tracer that can trace the origin of ore-forming materials, clarify mineralization patterns, and establish mineralization models, providing a theoretical basis for deep mineral exploration.

[0034] The first embodiment of this application discloses a method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area, such as... Figure 1As shown, it includes the following steps:

[0035] S1. After mixing silver powder and gold powder in a known proportion, the mixture is sintered and quenched to obtain a solid silver-gold standard sample.

[0036] S2. Cut the test sample and the solid silver-gold standard sample into fine particles with a diameter ≤1cm, cure them with epoxy resin and polish them to obtain the sample targets of the test sample and the standard sample.

[0037] S3. The sample targets of the test sample and the standard sample are ablated using laser to generate sample aerosol particles;

[0038] S4. After determining the homogeneity of the isotopic composition of the standard sample by random in-situ analysis, micro-copper-solution analysis was performed to obtain the silver isotope determination results, which were used as reference values ​​for the standard material.

[0039] S5. Subsequently, the standard sample and the sample target of the test sample were analyzed sequentially on the aerosol particles using a multi-receiver inductively coupled plasma mass spectrometer in the order of standard sample-test sample-standard sample. 109 Ag and 107 Ag, respectively, to obtain the silver isotope ratio of the standard sample target and the silver isotope ratio of the sample to be tested before the sample to be tested and after the sample to be tested.

[0040] S6. Correct the silver isotope ratio of the test sample using the silver isotope ratio of the target sample of the standard sample before and after the test sample analysis, and obtain the silver isotope ratio of the test sample relative to the reference value of the standard material mentioned in S3. Convert it to the value relative to the international standard NIST 978a, which is the silver isotope value of the test sample.

[0041] In this embodiment, the silver powder and gold powder are high-purity materials with a purity of 99.99%, and both are nanospheres with a particle size distribution of 100-400 nm. The sintering temperature is 1064-1100℃, and the temperature is maintained for 3 minutes after reaching the melting point of the gold powder. Subsequently, the molten mixed powder is removed and quenched in deionized water to obtain solid silver-gold particles. It should be noted that the standard sample mentioned in this application is a synthetic particle with a uniform Ag isotopic composition and different silver contents; the reference value is -0.24±0.02‰ (2sd, n=3). To avoid matrix effects caused by excessive differences in silver content between the standard sample and the test sample, an Ag content close to that of the test sample is generally selected as the configuration ratio of the standard sample. The silver content of natural silver-gold ore is generally 2%, 5%, or 10%. Therefore, the preferred Ag mass fraction in the standard sample of this application is 2%, 5%, or 10%.

[0042] In this embodiment, the preferred method for curing and polishing the sample particles with epoxy resin is as follows: the cut sample particles are placed inside a plastic ring with a diameter of 1 cm or 1 inch, and the plastic ring and sample particles are fixed on double-sided tape to ensure their relative positions. After this, an appropriate amount of epoxy resin is poured into the plastic ring that is fixed in the relative position. After the epoxy resin cures, the sample particles are fixed in the resin. The plastic ring is then removed, and the resin surface is polished until the sample particles are exposed. Subsequently, a finer polishing liquid is used for fine polishing to obtain a mineral surface close to a mirror finish, which is ready for laser ablation.

[0043] In this embodiment, the laser ablation described in S3 is femtosecond laser ablation. By adjusting the parameters of laser ablation (such as frequency, energy, beam spot, etc.), the deviation of the silver isotope signal intensity ratio between the sample to be tested and the standard sample is ≤20%.

[0044] In this embodiment, the laser ablation needs to achieve the following effects: ① The laser focus is on the sample surface to ensure that the area to be analyzed can be effectively ablated; the sample aerosol particles generated by ablation have the smallest possible particle size and uniform particle size distribution to obtain stoichiometric sample injection, while enabling the plasma part of the mass spectrometer to effectively ionize the sample aerosol particles; ② On the basis of ensuring the accuracy of mass spectrometer analysis, the area of ​​the ablation region should be minimized as much as possible to improve the spatial resolution of the sample.

[0045] The above-mentioned effect is achieved by adjusting the laser ablation parameters. For example, when ablating the sample target of the sample to be tested, in order to achieve the above-mentioned effect, it is preferable to focus the energy density on the sample surface at 1.5 joules / square centimeter, the laser beam spot size at 12 to 30 micrometers, and the laser repetition frequency at 4 to 6 Hz. At the same time, in order to obtain accurate analytical results, when ablating the standard sample, it is necessary to adjust the laser ablation parameters so that the signals of the standard sample and the sample to be tested are basically consistent, that is, the ratio of the intensity of the standard sample signal to the silver isotope signal of the sample to be analyzed is close to 1, and the deviation should not exceed 20%.

[0046] In a further embodiment, the random in-situ analysis of the standard sample described in S4 specifically involves: randomly selecting micro-area analysis sites and determining the uniformity of its silver isotope composition through a large number of random micro-area analysis results. Taking a silver-gold standard sample with a silver content of 2% as an example (total amount 1g, Ag / Au = 1:49), such as... Figure 2 As shown, the values ​​of the in-situ micro-area analysis were calculated to the international standard NIST 978a, and the overall result was -0.23±0.08‰ (2sd, n=82), which is consistent with the value determined by the solution chemical method. This proves that the standard material has a uniform silver isotope composition and is stable and reliable. It is suitable as a standard material for in-situ micro-area silver isotope analysis of silver-gold mines, and -0.24±0.02‰ (2sd, n=3) is used as its reference value.

[0047] It should be noted that in the analysis method described in S5, which follows the sequence of "standard sample - test sample - standard sample" (i.e., the SSB method), the same standard sample target is used. This standard sample is analyzed once before the test sample analysis to obtain the silver isotope ratio of the standard sample target analyzed before the test sample. After the test sample analysis, the same standard sample is analyzed again to obtain the silver isotope ratio of the standard sample target analyzed after the test sample. 109 Ag / 107 Ag value).

[0048] Furthermore, in step S6, the following formula is used for correction:

[0049]

[0050] Where, δ 109 Ag represents the silver isotope ratio of the sample to the reference value of the standard substance;

[0051] 109 Ag / 107 Agsam represents the sample to be tested. 109 Ag / 107 The value of Ag;

[0052] 109 Ag / 107 Ag std-B This indicates the standard sample target for analysis before the sample to be tested. 109 Ag / 107 The value of Ag;

[0053] 109 Ag / 107 Ag std-A This indicates the standard sample target for analysis after the sample to be tested. 109 Ag / 107 The value of Ag.

[0054] Furthermore, the correction yields δ 109 The Ag value is then converted to a value relative to the international standard NIST 978a using the following formula:

[0055] δ 109 Ag NIST978a =δ 109 Ag std-NIST978a +δ 109 Ag sam-std ;

[0056] Where, δ 109 Ag std-NIST 978a This indicates the value of the sample relative to the international Ag isotope standard NIST SRM 978a; δ109 Ag sam-std This indicates the sample's value relative to the reference standard.

[0057] The technical effects of the method of this application will be described in detail below through specific embodiments.

[0058] Example 1: A method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area

[0059] This embodiment uses silver-gold ore samples from the Xigou Gold-Copper Mine in Shanxi, China; the Qiyugou Gold Mine in Henan, China; the Qianhe Gold Mine in Henan, China; and the Baolun Gold Mine in Hainan, China as the samples to be tested.

[0060] 1. Each sample to be tested is cut using a diamond wire cutter to prepare fine particles with a diameter not exceeding 1 cm. The cut particles are then placed in a plastic ring with a diameter of 1 cm or 1 inch. The plastic ring and the sample particles are fixed on double-sided tape to ensure their relative positions. After completion, an appropriate amount of epoxy resin is poured into the plastic ring that is fixed in the relative position. After the epoxy resin cures, the sample particles are fixed in the resin. The plastic ring is removed and the resin surface is polished until the sample particles are exposed. Then, a finer polishing fluid is used for fine polishing to obtain a mineral surface close to a mirror finish, ready for laser ablation.

[0061] 2. The above sample targets were ablated using a femtosecond laser, with the energy density focused on the sample surface at 1.5 joules / square centimeter, the laser spot size at 12–30 micrometers, and the laser repetition frequency at 4–6 Hz, to obtain aerosol particles of each sample.

[0062] 3. A solid silver-gold standard sample was obtained by sintering and quenching silver powder and gold powder with an Ag mass fraction of 2%. Multiple standard material sample targets were prepared according to the method described in 1, and laser ablation was performed according to the method described in 2. Subsequently, the isotopic composition homogeneity of the standard sample was determined by random in-situ analysis, followed by micro-drilling-solution analysis to obtain the isotopic determination results, which were used as reference values ​​for the standard material (e.g., ...). Figure 2 The solution values ​​shown in Figure 2 were then analyzed by ionization of the aerosol particles of each test sample and standard sample using a multi-receiver inductively coupled plasma mass spectrometry (SSB method). The ionization analysis was performed sequentially in the order of standard sample-test sample-standard sample. The signal detection system detected the concentration of aerosol particles in the aerosol particles. 109 Ag and 107Ag was used to obtain the silver isotope ratio of each sample to be tested, as well as the isotope ratio of the standard samples analyzed before and after the sample to be tested. The silver isotope ratio of the sample to be tested was corrected using the silver isotope ratio of the standard sample targets analyzed before and after the sample to be tested, so as to obtain the silver isotope ratio of the sample to be tested relative to the reference value of the standard material. This value was then converted to the value relative to the international standard NIST 978a, which is the silver isotope value of the sample to be tested.

[0063] 4. Results are as follows Figure 3 As shown: by Figure 3 Taking Xigou as an example, the silver isotope composition of the particle was analyzed at five sites. Using a standard material with an Ag content of 2%, the Ag isotope ratio relative to the reference material was -0.23‰. This was then converted to the σ value relative to the international standard NIST 978a. 109 The Ag value is -0.47‰; wherein, the standard substance developed in this invention has a σ value relative to the international standard NIST 978a. 109 The Ag value is -0.24‰; the values ​​for the other four points are -0.34‰, -0.29‰, -0.39‰, and -0.43‰, respectively. This demonstrates that the method disclosed in this application can accurately identify minute changes in silver isotopes in a micro-region, with changes as small as 0.1‰ being effectively detected.

[0064] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A method for in-situ determination of silver isotopes in silver-gold ore samples in a micro-area, characterized in that, Includes the following steps: S1. After mixing silver powder and gold powder in a known proportion, the mixture is sintered and quenched to obtain a solid silver-gold standard sample. S2. Cut the test sample and the solid silver-gold standard sample into fine particles with a diameter ≤1cm, cure them with epoxy resin and polish them to obtain the sample targets of the test sample and the standard sample. S3. The sample targets of the test sample and the standard sample are ablated using laser to generate sample aerosol particles; S4. After determining the homogeneity of the isotopic composition of the standard sample by random in-situ analysis, micro-copper-solution analysis was performed to obtain the silver isotope determination results, which were used as reference values ​​for the standard material. S5. Subsequently, the standard sample and the sample target of the test sample were analyzed sequentially on the aerosol particles using a multi-receiver inductively coupled plasma mass spectrometer in the order of standard sample-test sample-standard sample. 109 Ag and 107 Ag, respectively, to obtain the silver isotope ratio of the standard sample target and the silver isotope ratio of the sample to be tested before the sample to be tested and after the sample to be tested. S6. Correct the silver isotope ratio of the test sample using the silver isotope ratio of the target of the standard sample before and after the test sample analysis, and obtain the silver isotope ratio of the test sample relative to the reference value of the standard material described in S3. Convert it to the value relative to the international standard NIST 978a, which is the silver isotope value of the test sample. In step S6, the following formula is used for correction: ； in, This indicates the silver isotope ratio of the sample to the reference value of the standard substance; Indicates the sample to be tested 109 Ag / 107 The value of Ag; This indicates the standard sample target for analysis before the sample to be tested. 109 Ag / 107 The value of Ag; This indicates the standard sample target for analysis after the sample to be tested. 109 Ag / 107 The value of Ag.

2. The method according to claim 1, characterized in that, The silver and gold powders mentioned in S1 are both nanospheres with a particle size distribution of 100-400 nm.

3. The method according to claim 1, characterized in that, In the known proportions of silver and gold powder, the mass fraction of silver powder is 2%, 5%, or 10%.

4. The method according to claim 1, characterized in that, The sintering temperature is 1064-1100℃, and the temperature is maintained for 3 minutes after reaching the melting point of the gold powder.

5. The method according to claim 1, characterized in that, The laser ablation described in S3 is femtosecond laser ablation, in which the ratio of silver isotope signal intensity between the sample to be tested and the standard sample is adjusted to be ≤20%.

6. The method according to claim 1, characterized in that, The transformation described in S6 is performed according to the following formula: ； in, This indicates the value of the sample relative to the international Ag isotope standard NIST SRM 978a; This indicates the sample relative to the reference value of the standard substance described in claim 1, S4.

Images