Method for determining age of fluorite mineral
By using U-Pb isotope dating and optimizing the test sequence list with laser ablation inductively coupled plasma mass spectrometry (ICP-MS), U-Pb age TW maps were plotted, solving the problem of difficult age determination for fluorite minerals. This approach achieves efficient and low-cost age acquisition, improving research accuracy and exploration efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2024-11-22
- Publication Date
- 2026-05-22
AI Technical Summary
The existing technology for obtaining Sm-Nd isochron ages of fluorite is cumbersome, and it is difficult to obtain samples from the same period with significant differences in isotope ratios, making it difficult to accurately determine the age of fluorite minerals.
A novel U-Pb isotope dating method was adopted, and fluorite minerals were tested using laser ablation inductively coupled plasma mass spectrometry. The test sequence list and detection process were optimized, and the laser in-situ U-Pb age TW map was plotted to calculate the age of fluorite minerals.
It enables rapid, efficient, and low-cost acquisition of fluorite mineral ages with an error of less than 3%, providing quantitative geochronological evidence and improving the exploration efficiency of fluorite-associated metallic minerals and natural gas reservoirs.
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Figure CN122072255A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of geology and thermochronology, and specifically to a method for determining the age of fluorite minerals. Background Technology
[0002] Fluorite, also known as fluorite mineral, is a common low-to-medium temperature hydrothermal mineral whose main component is calcium fluoride. Fluorite is widely used in emerging industries such as new energy and new materials, as well as in defense, military, nuclear industry, chemical industry, metallurgy, and building materials.
[0003] Fluorite minerals crystallize during geological events such as magmatism, metamorphism, and tectonic activity, becoming key minerals for studying magmatic, metamorphic, and tectonic processes. In specific geological environments, fluorite minerals can accumulate independently and co-occur with other metallic minerals such as wolframite and cassiterite, forming fluorite deposits or deposits of polymetallic tungsten, polymetallic tin, lead-zinc sulfides, iron-manganese, and rare earth elements, which are of significant indicative value for ore deposit research. In sedimentary basins, fluorite minerals often serve as authigenic minerals in the middle to late stages of diagenesis, recording the diagenetic process. Furthermore, in deep carbonate strata, the formation temperature of fluorite minerals is generally consistent with the peak gas generation temperature of source rocks, and authigenic or secondary methane inclusions are often found in fluorite minerals in deep carbonate strata, recording the deep natural gas accumulation process.
[0004] Determining the formation time of fluorite minerals is a key and challenging issue in geological and mineral deposit research. Currently, fluorite mineral dating generally uses fluorite Sm-Nd isotopic isochron ages to determine the age of fluorite (Halliday et al., 1990; Chesley et al., 1991; Han Wenbin et al., 1991; Peng Jiantang et al., 2003, 2006; Li Zejun, 2020). This mainly involves the study of the formation age of fluorite, tin, tungsten, MVT-type lead-zinc deposits, fluorite-(barite), and antimony deposits. However, obtaining Sm-Nd isotopic isochron ages of fluorite is relatively complicated, and samples from the same geological period with significantly different isotopic ratios are relatively difficult to obtain. Therefore, obtaining Sm-Nd isochron ages of fluorite is often challenging, making fluorite age determination difficult. Furthermore, the initial Nd isotope values in fluorite are heterogeneous and easily altered by geological events. Ideally, the obtained Sm-Nd isochron ages should be verified with data from other geochronologies, further increasing the difficulty of fluorite age determination. Therefore, developing a more convenient method for fluorite age determination is of great practical significance. Summary of the Invention
[0005] The purpose of this invention is to overcome the problems of existing technologies, such as the cumbersome experimental process for obtaining Sm-Nd isotope isochron ages of fluorite and the relative difficulty in obtaining samples from the same period with significant differences in isotope ratios, thus making it difficult to determine the age of fluorite minerals. This invention provides a method for determining the age of fluorite minerals. The method described in this invention avoids the drawbacks of existing technologies, which struggle to obtain Sm and Nd isotopes from fluorite. It employs a novel U-Pd isotope dating method to detect the age of fluorite minerals and successfully overcomes the difficulty of low U and Pd isotope content in fluorite. The detection method is also simpler, successfully reducing the difficulty of obtaining the age of fluorite minerals.
[0006] To achieve the above objectives, a first aspect of the present invention provides a method for determining the age of fluorite minerals, the method comprising the following steps: (1) Cut the fluorite mineral and use the cut fluorite mineral to make a target or probe to obtain the sample to be tested; (2) Perform petrological analysis on the sample to be tested and determine the location of the fluorite mineral to be tested in the sample; (3) The sample to be tested is loaded into the sample cell, a test sequence list is established, and the laser ablation inductively coupled plasma mass spectrometer is used to test the sample in the order of the test sequence list. The test data is analyzed, and the laser in-situ U-Pb age TW map of the sample to be tested is plotted to obtain the age of the sample to be tested. The test sequence list is established in the following order: blank-SRM614 standard sample, blank-standard sample A, blank-standard sample B, blank-sample to be tested, blank-SRM614 standard sample, blank-standard sample A and blank-standard sample B. Standard sample A is a fluorite mineral standard sample used to calibrate the elemental content obtained from the test, and standard sample B is a fluorite mineral standard sample used to monitor the data obtained from the test.
[0007] Preferably, when the sample to be tested is a sample target, the diameter of the sample target is ≤2.54cm and the thickness is ≤5mm; Preferably, when the sample to be tested is a probe sheet, the thickness of the probe sheet is ≥50μm, and more preferably 50-100μm.
[0008] Preferably, in step (2), the petrological analysis includes: taking pictures of the sample to be tested using transmitted light, reflected light and cathodic emission, and analyzing the obtained pictures.
[0009] Preferably, the SRM614 standard sample is a synthetic silicate glass SRM series standard glass sample.
[0010] Preferably, in step (3), the element tested using laser ablation inductively coupled plasma mass spectrometry is... 202 Hg, 204 Pb, 206 Pb, 207 Pb, 208 Pb, 232 Th and 238 U.
[0011] Preferably, in step (3), before testing the samples in the test sequence list using the laser ablation inductively coupled plasma mass spectrometer, the laser ablation inductively coupled plasma mass spectrometer needs to be calibrated. Preferably, the debugging method includes: continuously ablating a standard glass sample using a laser ablation inductively coupled plasma mass spectrometer, and debugging the laser ablation inductively coupled plasma mass spectrometer according to the collected mass spectrometry signal, so that the oxide content during the test is ≤1%.
[0012] Preferably, in step (3), after the sample to be tested is loaded into the sample cell, the sample cell and gas pipeline are flushed with carrier gas to remove the background Pb signal present in the sample cell and gas pipeline. Preferably, the carrier gas flushing time is 30-60 minutes.
[0013] Preferably, the laser beam spot during the laser ablation inductively coupled plasma mass spectrometry test is 30-90 μm, and the ablation frequency is 3-10 Hz.
[0014] Preferably, during the testing process, 5-10 sample points are inserted between the preceding and following standard samples for testing.
[0015] Preferably, when using a laser ablation inductively coupled plasma mass spectrometer for testing, the time interval between tests for each sample point is greater than or equal to the time required for the carrier gas purging ablation signal to decrease to the background value.
[0016] Preferably, the test sample is calibrated using the SRM614 standard sample. 207 Pb / 206 Pb isotope ratios; Preferably, the test sample is obtained by calibrating the standard sample A. 238 U / 206 Pb ratio; Preferably, the accuracy of the test results of the sample to be tested is monitored using the standard sample B.
[0017] This invention proposes a novel method for determining the age of fluorite minerals, overcoming the limitations of existing methods that rely on Sm-Nd isotope isochron ages, which suffer from difficulties in obtaining Sm-Nd isotope isochrons and stringent detection conditions. Furthermore, by optimizing the testing process and sequence, it successfully overcomes the challenge of low U and Pb isotope content in fluorite. Employing a novel U-Pb isotope isochronology method for fluorite age determination improves detection sensitivity and enables rapid, efficient, and low-cost in-situ laser-guided U-Pb ages of fluorite minerals. This allows for the determination of fluorite formation time, fracture activity time, and the formation time of associated metal deposits and natural gas reservoirs associated with fluorite, providing quantitative chronological evidence for related research and improving the exploration efficiency of fluorite-associated metal deposits and natural gas reservoirs. Attached Figure Description
[0018] Figure 1 This is a flowchart of the method for determining the age of fluorite minerals according to the present invention; Figure 2 This is the TW image of the laser in-situ U-Pb age of fluorite minerals obtained from Example 1. Figure 3 These are thin section photographs and optical microscope photographs of the rock sample to be tested in Example 2; Figure 4 This is the TW image of the laser in-situ U-Pb age of fluorite minerals obtained from Example 2. Figure 5 This is a photograph of the sample to be tested in Example 3; Figure 6 This is the laser in-situ U-Pb age TW map of fluorite minerals obtained from Example 3. Detailed Implementation
[0019] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0020] The flowchart of the method for determining the age of fluorite minerals described in this invention is as follows: Figure 1 As shown, the method includes the following steps: (1) Cut the fluorite mineral and use the cut fluorite mineral to make a target or probe to obtain the sample to be tested; (2) Perform petrological analysis on the sample to be tested and determine the location of the fluorite mineral to be tested in the sample; (3) The sample to be tested is loaded into the sample cell, a test sequence list is established, and the laser ablation inductively coupled plasma mass spectrometer is used to test the sample in the order of the test sequence list. The test data is analyzed, and the laser in-situ U-Pb age TW map of the sample to be tested is plotted to obtain the age of the sample to be tested.
[0021] In existing technologies, fluorite ages are obtained using Sm-Nd isotope isochron ages. However, the difficulty in obtaining Sm-Nd isochrones in fluorite increases the complexity of age determination. Furthermore, due to the low abundance of U and Pb isotopes in fluorite, there is currently no existing technology for U-Pb isotope dating to determine its age. The method described in this invention improves sensitivity by optimizing the testing process and establishing a test sequence list. It creatively employs U-Pb isotope dating to successfully determine the age of fluorite, providing a fast, efficient, and low-cost method with an error of approximately 3%. This fills a gap in current understanding of the difficulty in determining the age of fluorite minerals, provides quantitative chronological evidence for related research, and improves the exploration efficiency of fluorite-associated metal deposits and natural gas reservoirs.
[0022] In the method described in this invention, fluorite minerals are first selected according to research needs, and suitable rock samples and locations are chosen. The occurrence, distribution characteristics, formation period, and co-occurrence relationship of fluorite minerals with other minerals and surrounding rocks are described in detail and photographed. Then, the selected fluorite minerals are pretreated, and the selected samples and locations are cut according to the size of the laser pool to make epoxy resin sample targets or probe sheets, thus obtaining the samples to be tested.
[0023] In a preferred embodiment, when the sample to be tested is a sample target, the diameter of the sample target is ≤2.54cm and the thickness is ≤5mm. Specifically, the diameter of the sample target can be 2.54cm or 1.25cm, and the thickness can be 3-5mm.
[0024] In a preferred embodiment, when the sample to be tested is a probe sheet, the thickness of the probe sheet is ≥50μm, preferably 50-100μm.
[0025] In the method described in this invention, in step (2), petrological analysis is performed on the sample to be tested to further clarify the occurrence, distribution characteristics, formation period, and associated relationship of fluorite minerals with other minerals. Based on the research objective and the obtained petrological analysis results, the location of the fluorite minerals to be tested in the sample is determined, which serves as the target test point or test area for subsequent analysis and testing.
[0026] In some specific implementations, in step (2), the petrological analysis includes: taking pictures of the sample to be tested using transmitted light, reflected light and cathodic emission, and performing detailed petrological analysis on the obtained pictures to determine the subsequent test area or test point.
[0027] In the method described in this invention, a laser ablation inductively coupled plasma mass spectrometer is used to test the sample, and the elements tested are: 202 Hg, 204 Pb, 206 Pb, 207 Pb, 208 Pb, 232 Th and 238 U, based on the calibrated fluorite mineral obtained from the test 238 U / 206 Pb and 207 Pb / 206 Pb ratio, then use 238 U / 206 Pb is used as the x-axis. 207 Pb / 206 Using Pb as the ordinate, a laser in-situ U-Pb age TW map of the sample is plotted. The laser in-situ U-Pb age of the sample is then calculated, thereby determining the age of the fluorite mineral. The method for determining the age of fluorite minerals proposed in this invention provides a rapid, efficient, and low-cost method for obtaining the age of fluorite minerals.
[0028] In some specific embodiments, in step (3), the sample to be tested is placed between the sample cells, and the sample surface is wiped clean with anhydrous ethanol to remove any possible contamination. After the sample to be tested is placed into the sample cell, the laser ablation system is started, and the carrier gas flow rate is gradually increased to the set value. The carrier gas is used to flush the sample cell and gas pipeline to remove the background Pb signal present in the sample cell and gas pipeline. More preferably, the carrier gas flushing time is 30-60 minutes.
[0029] In a specific implementation, the carrier gas is helium.
[0030] In the method described in this invention, a test sequence list is established in the following order: blank-SRM614 standard sample, blank-standard sample A, blank-standard sample B, blank-sample to be tested, blank-SRM614 standard sample, blank-standard sample A, and blank-standard sample B. Specifically, in this invention, the blank-SRM614 standard sample refers to a blank test performed before testing the SRM614 standard sample. The blank test can be performed by directly testing air or by testing a blank sample. It can be understood that blank-standard sample A, blank-standard sample B, and blank-sample to be tested all refer to blank tests performed before testing standard sample A, standard sample B, and the sample to be tested.
[0031] In some specific implementations, the testing process follows a sequence of blank-SRM614 standard sample, blank-SRM614 standard sample, blank-standard sample A, blank-standard sample A, blank-standard sample B, blank-standard sample B, blank-test sample, ..., blank-test sample, blank-SRM614, blank-SRM614, blank-standard sample A, blank-standard sample A, blank-standard sample B, and blank-standard sample B. During the testing process, 5-10 sample points are inserted between each set of standard samples.
[0032] In the method described in this invention, standard sample A is a fluorite mineral standard sample, also known as fluorite standard sample A, used to calibrate the elemental content obtained from the test; standard sample B is a fluorite mineral standard sample, also known as fluorite standard sample B, used to monitor the data obtained from the test; and the SRM614 standard sample is a synthetic silicate glass SRM series standard glass sample. Specifically, in the method described in this invention, the SRM614 standard sample is used to calibrate the test results obtained from the sample to be tested. 207 Pb / 206 Pb isotope ratio; the standard sample A is used to calibrate the sample to be tested. 238 U / 206 Pb isotope ratio; the standard sample B is a quality monitoring standard used to monitor the quality of the test results of the sample to be tested and to monitor the accuracy of the test data. The accuracy of the detection is further improved by setting a test sequence list.
[0033] In some specific implementations, oxides are generated during the mass spectrometry detection process in step (3), and the generated oxides will interfere with the determination of the target element. Therefore, the laser ablation inductively coupled plasma mass spectrometer used needs to be debugged before the test.
[0034] In a preferred embodiment, the method for adjusting the laser ablation inductively coupled plasma mass spectrometer (LCP-MS) includes: continuously ablating a standard glass sample using the LCP-MS, and adjusting the LCP-MS based on the collected mass spectrometry signals to ensure that the oxide content during the testing process is ≤1%. The standard glass sample can be an SRM614 standard sample, an SRM612 standard sample, or an SRM610 standard glass. Specifically, the method for adjusting the LCP-MS based on the collected mass spectrometry signals can refer to the instrument's operation manual or common techniques in the art, and will not be elaborated here. After adjusting the LCP-MS, an analytical method of laser ablation-(MC)-ICP-MS is established, and the elements to be measured are selected to set the corresponding integration time and statistical method. The analytical method, integration time, and statistical method can be implemented according to common techniques in the art.
[0035] In some specific embodiments, appropriate laser beam spots and ablation frequencies are selected based on the U and Pb content of the fluorite mineral. In the method described in this invention, the laser beam spot used for laser ablation inductively coupled plasma mass spectrometry (ICP-MS) testing is 30-90 μm, and the ablation frequency is 3-10 Hz. Specifically, the laser beam spot used for laser ablation ICP testing is 30 μm, 50 μm, or 90 μm, and the ablation frequency is 3 Hz.
[0036] In some specific embodiments, when using a laser ablation inductively coupled plasma mass spectrometer (LAMS) for testing, the time interval between tests for each sample point is greater than or equal to the time required for the carrier gas purging ablation signal to decrease to the background value. Preferably, the time interval between tests for each sample point is 5-20 seconds, more preferably 8-15 seconds. Specifically, the time interval between tests for each sample point as described in this invention refers to the time interval between the end of the previous sample point test and the beginning of the next sample point test when using a laser ablation LAMS.
[0037] In the method described in this invention, the calibrated fluorite mineral is obtained based on the test. 238 U / 206 Pb and 207 Pb / 206 Using Pb ratio data, laser in-situ U-Pb age TW maps of fluorite minerals were constructed using Isoplot or other plotting software. Then, U-Pb isotope dating was performed on the fluorite minerals to calculate the laser in-situ U-Pb age of the samples. The specific calculation method involved projecting each sample point onto the TW map, then performing a linear fit on the data points, with the lower intersection age representing the fluorite mineral age. Finally, based on previous sample observations and rock and mineral analysis results, the obtained laser in-situ U-Pb ages of the fluorite minerals were interpreted.
[0038] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.
[0039] Example 1 The fluorite minerals selected in this embodiment were derived from the third phase of fault activity on the southern margin of the Tarim Basin, and the determination method is as follows: (1) Sampling, and detailed description and photographic record of the occurrence, distribution characteristics, formation period and co-occurrence relationship of fluorite minerals with other minerals and surrounding rocks; (2) Based on the size of the laser pool, the selected sample and part are cut to make a fluorite sample target (the sample target diameter is 2.54 cm and the thickness is 3 mm); (3) Photographing: The sample target is photographed using transmitted light, reflected light, and cathodic emission, and petrological analysis is performed to further clarify the occurrence, distribution characteristics, formation period, and association relationship of fluorite minerals with other minerals. Based on the research objectives and petrological analysis results, the location of the fluorite minerals to be tested is determined; (4) Wipe the surface of the fluorite sample target clean with anhydrous ethanol, and then put it into the sample cell. Start the laser ablation system according to the instrument operation manual. Gradually increase the carrier gas (He gas) flow rate to 750 ml / min and continuously rinse the sample cell and gas pipeline for more than 30 minutes to remove the background Pb that may be present in the sample cell and gas pipeline. (5) Establish a test sequence list. During the test, the test procedure is as follows: blank-SRM614 standard sample, blank-SRM614 standard sample, blank-standard sample A, blank-standard sample A, blank-standard sample B, blank-standard sample B, blank-test sample, ..., blank-test sample, blank-SRM614 standard sample, blank-SRM614 standard sample, blank-standard sample A, blank-standard sample A, blank-standard sample B and blank-standard sample B. Ten sample points are inserted between the two sets of standards. (6) The laser ablation inductively coupled plasma mass spectrometer was debugged. The SRM614 sample was continuously ablated, and the sensitivity, stability and oxide yield of the mass spectrometer were optimized and debugged according to the collected mass spectrometry signal so that the oxide content during the test was ≤1%. The laser ablation inductively coupled plasma mass spectrometer analysis method was established, the elements to be measured were selected, and the corresponding integration time and statistical method were set. (7) The standard samples and the test samples were etched and analyzed in the order of the test sequence list using a laser ablation inductively coupled plasma mass spectrometer. Each sample point was analyzed. 202 Hg, 204 Pb, 206 Pb, 207 Pb,208 Pb, 232 Th, and 238 U elements; Select a laser beam spot of 50 μm and an ablation frequency of 3 Hz according to the U and Pb contents in the fluorite mineral to be measured; The measurement time interval for each test point is 8 s; (8) Calibrate the fluorite mineral to be measured using the data of the SRM614 standard sample 207 Pb / 206 Pb isotope ratio; Fluorite standard sample A is used to calibrate the fluorite mineral to be measured 238 U / 206 Pb ratio; Fluorite standard sample B is a fluorite standard mineral with known recommended values, which is analyzed together with the fluorite sample to be measured and used to monitor the quality of the test results; (9) According to the calibrated fluorite mineral to be measured obtained from the test 238 U / 206 Pb and 207 Pb / 206 Pb ratios, use Isoplot to compile a laser in-situ U-Pb age T-W diagram of the fluorite mineral, as Figure 2 shown, and calculate that the formation times of the three phases of fluorite samples in the fault zone are 426 ± 13 Ma, 355 ± 10 Ma, and 280 ± 17 Ma respectively.
[0040] Interpret the laser in-situ U-Pb age of the obtained fluorite mineral according to the previous sample observations and petrographic analysis results.
[0041] Example 2 The fluorite mineral selected in this example is from the fluorite in the Sinian Dengying Formation reservoir in the Sichuan Basin, and the measurement method is as follows: (1) Sampling, and describe in detail, photograph and record the occurrence, distribution characteristics, formation stages of the fluorite mineral and its coexistence relationship with other minerals and surrounding rocks; (2) According to the size of the laser cell, cut the selected sample and part into a fluorite sample target (the diameter of the sample target is 2.54 cm and the thickness is 3 mm); (3) Take pictures of the sample target through transmitted light, reflected light and cathodoluminescence and conduct petrographic analysis to further clarify the occurrence, distribution characteristics, formation stages of the fluorite mineral and its coexistence relationship with other minerals. According to the research purpose and the results of petrographic analysis, calibrate the position of the fluorite mineral to be measured (as Figure 3 shown, where Figure 3 a is a thin section photograph of the sample to be measured, Figure 3 b is an optical microscope photograph of the position of the fluorite mineral to be measured); (4) Wipe the surface of the fluorite sample target clean with anhydrous ethanol, and then put it into the sample cell. Start the laser ablation system according to the instrument operation manual. Gradually increase the carrier gas (He gas) flow rate to 750 ml / min and continuously rinse the sample cell and gas pipeline for more than 30 minutes to remove the background Pb that may be present in the sample cell and gas pipeline. (5) Establish a test sequence list. During the test, the test procedure is as follows: blank-SRM614 standard sample, blank-SRM614 standard sample, blank-standard sample A, blank-standard sample A, blank-standard sample B, blank-standard sample B, blank-test sample, ..., blank-test sample, blank-SRM614 standard sample, blank-SRM614 standard sample, blank-standard sample A, blank-standard sample A, blank-standard sample B and blank-standard sample B. Ten sample points are inserted between the two sets of standards. (6) The laser ablation inductively coupled plasma mass spectrometer was debugged. The SRM614 sample was continuously ablated, and the sensitivity, stability and oxide yield of the mass spectrometer were optimized and debugged according to the collected mass spectrometry signal so that the oxide content during the test was ≤1%. The laser ablation inductively coupled plasma mass spectrometer analysis method was established, the elements to be measured were selected, and the corresponding integration time and statistical method were set. (7) The standard samples and the test samples were etched and analyzed in the order of the test sequence list using a laser ablation inductively coupled plasma mass spectrometer. Each sample point was analyzed. 202 Hg, 204 Pb, 206 Pb, 207 Pb, 208 Pb, 232 Th and 238 U element; the laser beam spot size was selected as 50 μm and the ablation frequency as 3 Hz based on the U and Pb content in the fluorite mineral to be tested; the measurement time interval for each test point was 8 s; (8) Calibrate the fluorite minerals to be tested using data from the SRM614 standard sample. 207 Pb / 206 Pb isotope ratio; Fluorite standard sample A is used to calibrate the fluorite mineral to be tested. 238 U / 206 Pb ratio; Fluorite standard sample B is a fluorite standard mineral with a known recommended value, which is analyzed along with the fluorite sample to be tested to monitor the quality of the test results; (9) The calibrated fluorite mineral obtained from the test 238 U / 206 Pb and 207 Pb / 206Pb ratios were used to construct laser in-situ U-Pb age TW maps of fluorite minerals using Isoplot, such as... Figure 4 As shown, the formation time of the fluorite sample was calculated to be 257±12 Ma.
[0042] Based on previous sample observations and rock and mineral analysis results, the obtained laser in-situ U-Pb ages of fluorite minerals are interpreted.
[0043] Example 3 The fluorite mineral used in this embodiment is derived from Ordovician fracture-filled fluorite in the northwestern region of the Tarim Basin. The determination method is as follows: (1) Sampling, and detailed description and photographic record of the occurrence, distribution characteristics, formation period, and association relationship of fluorite minerals with other minerals and surrounding rocks (e.g. Figure 5 (as shown) (2) Based on the size of the laser pool, the selected sample and part are cut to make a fluorite sample target (the sample target diameter is 2.54 cm and the thickness is 3 mm); (3) The sample target was photographed using transmitted light, reflected light, and cathodic emission, and petrological analysis was performed to further clarify the occurrence, distribution characteristics, formation period, and association relationship of fluorite minerals with other minerals. Based on the research objectives and petrological analysis results, the location of the fluorite minerals to be tested was determined; (4) Wipe the surface of the fluorite sample target clean with anhydrous ethanol, and then put it into the sample cell. Start the laser ablation system according to the instrument operation manual. Gradually increase the carrier gas (He gas) flow rate to 750 ml / min and continuously rinse the sample cell and gas pipeline for more than 30 minutes to remove the background Pb that may be present in the sample cell and gas pipeline. (5) Establish a test sequence list. During the test, the test procedure is as follows: blank-SRM614 standard sample, blank-SRM614 standard sample, blank-standard sample A, blank-standard sample A, blank-standard sample B, blank-standard sample B, blank-test sample, ..., blank-test sample, blank-SRM614 standard sample, blank-SRM614 standard sample, blank-standard sample A, blank-standard sample A, blank-standard sample B and blank-standard sample B. Ten sample points are inserted between the two sets of standards. (6) The laser ablation inductively coupled plasma mass spectrometer was debugged. The SRM614 sample was continuously ablated, and the sensitivity, stability and oxide yield of the mass spectrometer were optimized and debugged according to the collected mass spectrometry signal so that the oxide content during the test was ≤1%. The laser ablation inductively coupled plasma mass spectrometer analysis method was established, the elements to be measured were selected, and the corresponding integration time and statistical method were set. (7) The standard samples and the test samples were etched and analyzed in the order of the test sequence list using a laser ablation inductively coupled plasma mass spectrometer. Each sample point was analyzed. 202 Hg, 204 Pb, 206 Pb, 207 Pb, 208 Pb, 232 Th and 238 U element; the laser beam spot size was selected as 50 μm and the ablation frequency as 3 Hz based on the U and Pb content in the fluorite mineral to be tested; the measurement time interval for each test point was 10 s; (8) Calibrate the fluorite minerals to be tested using data from the SRM614 standard sample. 207 Pb / 206 Pb isotope ratio; Fluorite standard sample A is used to calibrate the fluorite mineral to be tested. 238 U / 206 Pb ratio; Fluorite standard sample B is a fluorite standard mineral with a known recommended value, which is analyzed along with the fluorite sample to be tested to monitor the quality of the test results; (9) The calibrated fluorite mineral obtained from the test 238 U / 206 Pb and 207 Pb / 206 Pb ratios were used to construct laser in-situ U-Pb age TW maps of fluorite minerals using Isoplot, such as... Figure 6 As shown, the formation time of the fluorite sample was calculated to be 379±10 Ma.
[0044] Based on previous sample observations and rock and mineral analysis results, the obtained laser in-situ U-Pb ages of fluorite minerals are interpreted.
[0045] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A method for determining the age of fluorite minerals, characterized in that, The method includes the following steps: (1) Cut the fluorite mineral and use the cut fluorite mineral to make a target or probe to obtain the sample to be tested; (2) Perform petrological analysis on the sample to be tested and determine the location of the fluorite mineral to be tested in the sample; (3) The sample to be tested is loaded into the sample cell, a test sequence list is established, and the laser ablation inductively coupled plasma mass spectrometer is used to test the sample in the order of the test sequence list. The test data is analyzed, and the laser in-situ U-Pb age TW map of the sample to be tested is plotted to obtain the age of the sample to be tested. The test sequence list is established in the following order: blank-SRM614 standard sample, blank-standard sample A, blank-standard sample B, blank-sample to be tested, blank-SRM614 standard sample, blank-standard sample A and blank-standard sample B. Standard sample A is a fluorite mineral standard sample used to calibrate the elemental content obtained from the test, and standard sample B is a fluorite mineral standard sample used to monitor the data obtained from the test.
2. The method according to claim 1, characterized in that, When the sample to be tested is a sample target, the diameter of the sample target is ≤2.54cm and the thickness is ≤5mm; and / or When the sample to be tested is a probe sheet, the thickness of the probe sheet is ≥50μm, preferably 50-100μm.
3. The method according to claim 1, characterized in that, In step (2), the petrological analysis includes: taking pictures of the sample to be tested using transmitted light, reflected light and cathodic emission, and analyzing the obtained pictures.
4. The method according to claim 1, characterized in that, The SRM614 standard sample is a synthetic silicate glass SRM series standard glass sample.
5. The method according to claim 1, characterized in that, In step (3), the elements tested using laser ablation inductively coupled plasma mass spectrometry are: 202 Hg, 204 Pb, 206 Pb, 207 Pb, 208 Pb, 232 Th and 238 U.
6. The method according to claim 1 or 5, characterized in that, In step (3), before testing the samples in the test sequence list using the laser ablation inductively coupled plasma mass spectrometer, the laser ablation inductively coupled plasma mass spectrometer needs to be calibrated. Preferably, the debugging method includes: continuously ablating a standard glass sample using a laser ablation inductively coupled plasma mass spectrometer, and debugging the laser ablation inductively coupled plasma mass spectrometer according to the collected mass spectrometry signal, so that the oxide content during the test is ≤1%.
7. The method according to claim 1, 5, or 6, characterized in that, In step (3), after the sample to be tested is loaded into the sample cell, the sample cell and gas pipeline are flushed with carrier gas to remove the background Pb signal present in the sample cell and gas pipeline. Preferably, the carrier gas flushing time is 30-60 minutes.
8. The method according to any one of claims 1-7, characterized in that, The laser beam spot used in the laser ablation inductively coupled plasma mass spectrometer test was 30-90 μm, and the ablation frequency was 3-10 Hz.
9. The method according to any one of claims 1-8, characterized in that, During the testing process, 5-10 sample points are inserted between the preceding and following standard samples for testing; and / or When using a laser ablation inductively coupled plasma mass spectrometer for testing, the time interval between tests for each sample point is greater than or equal to the time required for the carrier gas purging ablation signal to decrease to the background value.
10. The method according to claim 1, characterized in that, The SRM614 standard sample is used to calibrate the sample under test. 207 Pb / 206 Pb isotope ratio; and / or The standard sample A is used to calibrate the sample to be tested. 238 U / 206 Pb ratio; and / or The standard sample B is used to monitor the accuracy of the test results of the sample to be tested.