A method for determining rare earth element content in garnet based on thermal infrared spectroscopy

Abstract

The present invention discloses a method for determining the rare earth element content of garnet based on thermal infrared spectroscopy, comprising the following steps: determining the rare earth element content m of a series of garnets; obtaining thermal infrared spectra of the corresponding garnets between 10 μm and 14 μm, and performing baseline correction; using the baseline of the thermal infrared spectra as the base, obtaining the closed area value n between the starting point, the end point, and the base of the first reflection peak appearing in the thermal infrared spectra; establishing a relationship curve model between m and n; and collecting the closed area value between the starting point, the end point, and the base of the first reflection peak of the garnet to be tested according to the above method, and obtaining the rare earth element content value of the garnet to be tested based on the relationship curve model. The method for determining the rare earth element content of garnet provided by the present invention is simple and easy to implement, can quickly obtain the REE content of a series of garnets, and lays a foundation for the study of water-rock conditions in hydrothermal systems.

Description

Technical Field

[0001] The present invention relates to the technical field of ore detection, and in particular to a method for determining the rare earth element content of garnet based on thermal infrared spectroscopy. Background Art

[0002] Garnet is a common isometric silicate mineral with an island structure, named for its crystals' resemblance to pomegranate seeds in shape and color. Its general chemical formula is X3Y2(SiO4)3, where X represents divalent cations, primarily magnesium, iron, manganese, and calcium; and Y represents trivalent cations, primarily aluminum, iron, chromium, and titanium. In garnet's crystal structure, silicon and oxygen atoms form silicon-oxygen tetrahedra. These tetrahedra and trivalent cations directly connect to form dodecahedrons, while divalent cations fill the ligand gaps and form dodecahedrons with the two oxygen atoms in the tetrahedra. Divalent cations are located at the X position of the dodecahedron, while trivalent cations are located at the Y position of the octahedron. Garnet generally has a well-defined crystal shape, often appearing as rhombic dodecahedrons and tetrahedrons. It exhibits no cleavage, a jagged fracture, and a glassy to adamantine luster. It is translucent, has a high Mohs hardness (6.5-7.5), and a high density (3.1-4.3 g / cm 3 ), high melting point (1180-1200℃), aggregates are dense blocks or granules.

[0003] Rare earth elements (REEs) are the lanthanide elements in the periodic table of chemical elements - lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the 15 closely related elements of the lanthanide series - yttrium (Y) and scandium (Sc). Garnet is widely present in skarn mineralization systems. Hydrothermal garnets record the process of fluid-rock interaction. The rare earth element and trace element signatures in these garnets can indicate the water-rock conditions of the hydrothermal system. Y and REEs exhibit very similar geochemical behaviors. Previous studies have shown a significant positive correlation between Y and total REEs, indicating that garnets formed under equilibrium conditions without fluid mixing, likely in a relatively closed system. However, the lack of a positive correlation between Y and total REEs suggests that garnets crystallized under non-equilibrium conditions, possibly with the mixing of different fluids and a significant compositional variation. Strong water-rock reactions (or large-scale permeability and metasomatism) tend to increase the total rare earth element content in skarns. The intensification of water-rock reactions and the increase in oxygen fugacity are important factors in the precipitation and enrichment of certain metals (such as tin). Therefore, the rapid determination of REE content in garnets is of great significance for the study of mineralization mechanisms. Summary of the Invention

[0004] Based on the above background, the main purpose of the present invention is to provide a new method for quickly determining the rare earth element content of garnet based on thermal infrared spectroscopy.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for determining the rare earth element content of garnet based on thermal infrared spectroscopy, comprising the following steps:

[0007] 1) Determine the rare earth element content m of a series of garnets;

[0008] 2) Obtain the thermal infrared spectrum of the corresponding garnet between 10 μm and 14 μm and perform baseline correction;

[0009] 3) taking the baseline of the thermal infrared spectrum as the bottom edge, obtaining a closed area value n between the starting point, the end point and the bottom edge of the first reflection peak appearing in the thermal infrared spectrum;

[0010] 4) Establish a relationship curve model with m as the horizontal coordinate and n as the vertical coordinate; or with n as the horizontal coordinate and m as the vertical coordinate;

[0011] 5) Collecting a thermal infrared spectrum of the garnet to be tested between 10 μm and 14 μm, performing baseline correction, taking the baseline of the thermal infrared spectrum as the base, obtaining the closed area value between the starting point to the end point and the base of the first reflection peak appearing in the thermal infrared spectrum, and obtaining the rare earth element content value of the garnet to be tested according to the relationship curve model of step 4).

[0012] Preferably, in step 1), the series of garnets are of the same variety.

[0013] More preferably, the varieties of garnet in step 1) and step 5) are also the same.

[0014] In the present invention, the same variety means that the coordination substitution mechanism of the garnet REEs is the same.

[0015] The present invention found that garnet has three characteristic reflection peaks in the thermal infrared spectrum between 10μm and 14μm. The reflection peaks are generated by the asymmetric stretching vibration of the Si-O bond in its silicon-oxygen tetrahedron. Specifically, when the REE enters the X position of the garnet dodecahedron, in order to maintain the balance of charge, the trivalent cations (Fe 3+ 、Al 3+ions (e.g., ions) can also replace Si in tetrahedrons, affecting the vibration of Si-O bonds and thus causing a corresponding change in the garnet's thermal infrared spectral response. Therefore, the position and intensity of the characteristic reflection peaks between 10μm and 14μm vary slightly between different garnet varieties, but the overall differences are not significant. A relationship curve model between m and n can be established to invert the REE content in garnet across varieties, meeting general work requirements. However, for work requiring higher precision, a relationship curve model can be established for each garnet variety to more accurately invert the REE content in garnet.

[0016] Preferably, the thermal infrared spectrum is measured by a LUMOS Fourier transform infrared spectrometer.

[0017] Preferably, the rare earth element content value m is measured by laser ablation inductively coupled plasma mass spectrometry.

[0018] Preferably, the highest point of the first reflection peak is between 11 μm and 12 μm.

[0019] In a second aspect, the present invention provides a method for determining the rare earth element content of garnet based on thermal infrared spectroscopy, comprising the following steps:

[0020] (1) Obtain a thermal infrared spectrum of the garnet to be tested between 10 μm and 14 μm and perform baseline correction;

[0021] (2) Taking the baseline of the thermal infrared spectrum as the bottom edge, obtain the closed area value n between the starting point, the end point and the bottom edge of the first reflection peak appearing in the thermal infrared spectrum;

[0022] (3) Obtaining the rare earth element content m of the garnet to be tested according to formula I,

[0023] m(±3ppm)=2489.04×n-145.421 Formula I;

[0024] Wherein, in step 1), the coordination substitution mechanism of the rare earth element in the garnet to be tested is a yttrium aluminum garnet (YAG) type substitution mechanism.

[0025] Preferably, the thermal infrared spectrum is measured by a LUMOS Fourier transform infrared spectrometer.

[0026] Preferably, the highest point of the first reflection peak is between 11 μm and 12 μm.

[0027] In addition, unless otherwise specified, any range described in the present invention includes the end value and any numerical value between the end values and any sub-range formed by the end value or any numerical value between the end values.

[0028] The beneficial effects of the present invention are as follows:

[0029] The present invention uses thermal infrared spectroscopy to analyze rock and mineral composition. Specifically, it proposes for the first time to use the characteristic reflection peak area of garnet's thermal infrared spectrum to invert its REE content, and thus provides a new method for quickly determining the REE content of garnet, which to some extent fills the gap in research in this area.

[0030] The method for determining the rare earth element content of garnet based on thermal infrared spectroscopy provided by the present invention is simple, easy to implement and has high accuracy, and can provide new ideas for the study of water-rock conditions in hydrothermal systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 Thermal infrared spectra of 12 garnet single minerals of different colors according to the embodiment are shown.

[0033] Figure 2 A thermal infrared spectrum of a single garnet mineral in the embodiment between 10 μm and 14 μm is shown.

[0034] Figure 3 A regression analysis chart showing the S1 area and REE content of 10 garnet minerals of different colors in the example is shown. DETAILED DESCRIPTION

[0035] To make the technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0036] The thermal infrared spectrum test of the following examples was completed in the Beijing Key Laboratory of Mineral Environment Function of Peking University, and the microscopic infrared spectrum of the garnet single mineral was collected using a Bruker LUMOS Fourier transform infrared spectrometer of Peking University.

[0037] The micro-area trace element contents in the following examples were determined using LA-ICP-MS at Guangzhou Tuoyan Testing Technology Co., Ltd. The laboratory used an NWR193UC laser ablation system, which consists of an NWR 193nm ArF excimer laser and an optical system, and an ICP-MS model of iCAP RQ.

[0038] Example

[0039] 1. Testing process: In this case, 12 garnet minerals of different colors were randomly selected from the Jiama deposit in Tibet, and micrometer-level microscopic infrared spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to determine the trace elements in the garnets.

[0040] 1.1 Thermal infrared spectrum test: the test wavelength range is 600cm -1 ~7000cm -1 (1.42μm~16.67μm), spectral resolution is 2cm -1 , scan the sample and background 64 times, the condenser is 10μm. The thermal infrared spectrum result of each sample is the average value of the measured value. The thermal infrared spectrum of each sample is stacked and plotted using Origin 2021 software. The results are shown in the figure. Figure 1 ,Depend on Figure 1 It can be seen that the main characteristics of the garnet infrared spectrum are between 10μm and 14μm. Therefore, after baseline correction, we will extract the infrared spectrum of garnet between 10μm and 14μm for analysis. Taking one of the samples as an example, the infrared spectrum of the garnet sample between 10μm and 14μm is shown in Figure 2. Figure 2 As shown, there are three reflection peaks and two absorption valleys between 10μm and 14μm. Reflection peak C (the second reflection peak) and secondary absorption valley are not obvious or absent in some samples. Therefore, we focus on reflection peak B (the first reflection peak), reflection peak D (the third reflection peak), and absorption valley T (the first absorption valley). Using Origin 2021 software, curve integration of the S1, S2, and S3 areas of the 11 samples was performed to determine the reflection peak intensity and the T absorption valley depth. The spectral parameter measurement results are shown in Table 1 below.

[0041] 1.2 Micro-area trace element content test: The laser ablation system uses helium as the carrier gas during the laser ablation process. The laser ablation system is equipped with a signal smoothing device. The laser beam spot, energy, and frequency for this analysis are 30 μm, 3.5 J / cm, and 1.5 J / cm, respectively. 2 and 6 Hz. Single-mineral trace element content analysis used glass reference materials (NIST 610 and NIST 612) for multiple external standard calibration without internal standard. Trace element content for each sample was the average of measurements taken at multiple points on the sample slice. Each time-resolved analysis data set included approximately 30 s of blank signal and 40 s of sample signal. Offline data processing (including sample and blank signal selection, instrument sensitivity drift correction, and elemental content analysis) was performed using the ICPMSDataCal software. REE content test results are shown in Table 2 below.

[0042] 2. Test Results Analysis

[0043] This experimental analysis used IBM's SPSS software to conduct a correlation analysis between the REE content of 10 samples (excluding abnormal sample points) and the pairwise variables of the statistical spectral parameters (see Table 3 for the results). It can be seen from the data in Table 3 that there is a good correlation between the REE content in garnet and the B and D peak intensities. The closer the absolute value of the correlation coefficient in the table is to 1, the better the correlation between the two variables, and a negative number indicates a negative correlation. In addition to peak intensity, the B and D peak areas S2 and S3 also show a certain correlation with the REE content, but their areas will be affected by the depth of the T absorption valley. Judging from the final experimental results, the correlation between the S1 area of the garnet thermal infrared spectrum and the REE content is the best, with a correlation coefficient of up to 0.959. Origin 2021 software was used to perform regression analysis on the S1 area and REE content (excluding abnormal sample points, fitting results see Figure 3 ), and its linear fit goodness R 2 is greater than 0.91, indicating that more sample points fall near the regression line. It is feasible and accurate to use the S1 area of the garnet thermal infrared spectrum to invert the REE content. Figure 2 , it can be understood that S1 area = the closed area value between the peak curve and the baseline from the starting point to the end point of the B reflection peak, combined with Figure 3 The relationship between the S1 area (n) and the REE content (m) can be obtained as follows:

[0044] m(±3ppm)=2489.04×n-145.421.

[0045] Table 1:

[0046] Sample number B peak intensity D peak intensity T valley depth S1 area S2 area S3 area ZK028-10027 0.1387 0.1494 0.6470 0.0663 0.0235 0.1131 ZK028-975 0.1229 0.1336 0.5910 0.0603 0.0189 0.0763 ZK028-973 0.1375 0.1408 0.5500 0.0726 0.0196 0.0663 ZK028-10027-1 0.1378 0.1503 0.6780 0.0639 0.0248 0.1229 ZK028-975-1 0.1324 0.1437 0.6110 0.0627 0.0208 0.0849 ZK028-973-1 0.1314 0.1420 0.6380 0.0597 0.0215 0.0860 ZK2407-357.1 0.1459 0.1572 0.6540 0.0738 0.0260 0.1239 ZK028-973-2 0.1215 0.1299 0.4850 0.0596 0.0168 0.0661 ZK028-916.2 0.1316 0.1402 0.6320 0.0636 0.0220 0.1041 ZK2418-848.4 0.1209 0.1281 0.6240 0.0603 0.0207 0.1006 ZK028-937.1 0.1235 0.1307 0.6240 0.0620 0.0207 0.1007

[0047] Table 2:

[0048] Sample number REE / ppm ZK028-10027 21.4955 ZK028-975 5.8147 ZK028-10027-1 18.8306 ZK028-975-1 5.4917 ZK028-973-1 2.3072 ZK2407 357.1 38.3662 ZK028-909.6 8.4902 ZK028-973-2 5.3970 ZK028-916.2 8.8635 ZK2418-848.4 6.5669 ZK028-937.1 6.2809

[0049] Table 3:

[0050]

[0051] **. The correlation is significant at the 0.01 level (two-tailed).

[0052] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for determining the rare earth element content of garnet based on thermal infrared spectroscopy, characterized in that: The following steps are involved: 1) Determine the rare earth element content m of a series of garnets; 2) Obtain the thermal infrared spectrum of the corresponding garnet between 10 μm and 14 μm and perform baseline correction; 3) Taking the baseline of the thermal infrared spectrum as the bottom edge, obtaining a closed area value n between the starting point, the end point and the bottom edge of the first reflection peak appearing in the thermal infrared spectrum; 4) Take m as the horizontal coordinate and n as the vertical coordinate; Or use n as the horizontal coordinate and m as the vertical coordinate to establish a relationship curve model; 5) Acquire a thermal infrared spectrum of the garnet to be tested between 10 μm and 14 μm, perform baseline correction, and use the baseline of the thermal infrared spectrum as the base. Obtain the closed area between the starting point and the end point of the first reflection peak appearing in the thermal infrared spectrum and the base. Determine the rare earth element content of the garnet to be tested based on the relationship curve model of step 4).

2. The determination method according to claim 1, characterized in that In step 1), the series of garnets are of the same variety.

3. The determination method according to claim 2, characterized in that: In step 1) and step 5), the variety of garnet is the same.

4. The determination method according to claim 1, characterized in that The thermal infrared spectrum is measured by a LUMOS Fourier transform infrared spectrometer.

5. The determination method according to claim 1, characterized in that: The rare earth element content value m is measured by laser ablation inductively coupled plasma mass spectrometry.

6. The determination method according to claim 1, characterized in that: The highest point of the first reflection peak is between 11 μm and 12 μm.

7. A method for determining the rare earth element content of garnet based on thermal infrared spectroscopy, characterized in that: The following steps are involved: (1) Obtain the thermal infrared spectrum of the garnet to be tested between 10 μm and 14 μm and perform baseline correction; (2) Taking the baseline of the thermal infrared spectrum as the bottom edge, obtain the closed area value n between the starting point, the end point and the bottom edge of the first reflection peak appearing in the thermal infrared spectrum; (3) Obtaining the rare earth element content m of the garnet to be tested according to formula І, m±3 ppm = 2489.04×n - 145.421 formula І; Wherein, in step 1), the coordination substitution mechanism of the rare earth element in the garnet to be tested is a yttrium aluminum garnet type substitution mechanism.

8. The determination method according to claim 7, characterized in that: The thermal infrared spectrum is measured by a LUMOS Fourier transform infrared spectrometer.

9. The determination method according to claim 7, characterized in that: The highest point of the first reflection peak is between 11 μm and 12 μm.

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