Dolomite standard sample development method calibrated by age method, dolomite standard sample, and use thereof

Abstract

The present invention provides a dolomite standard sample development method calibrated by an age method, a dolomite standard sample and the use thereof. The development method comprises: providing a candidate of a dolomite standard sample; providing a calcite standard sample, a zircon standard sample and a garnet standard sample which have been subjected to verification of matrix effects; taking the calcite standard sample as a main standard sample, and the zircon standard sample and the garnet standard sample as secondary standard samples, measuring the age of the candidate of the dolomite standard sample twice, and marking the test results as A and B; and when A and B satisfy (A-B) / B×100≤3, using the candidate of the dolomite standard sample as a dolomite standard sample.

Description

A dolomite standard sample development method for calibrating by age method, dolomite standard sample and its application

[0001] Cross-reference information

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on November 7, 2023, with application number 202311473484.7 and invention name “A method for developing a dolomite standard sample calibrated by age method, dolomite standard sample and its application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the field of petroleum and natural gas geological exploration, and in particular to a method for developing a dolomite standard sample calibrated by an age method, a dolomite standard sample and applications thereof. Background Art

[0004] Geochronology is a perennial theme in geological research, widely applicable to paleoenvironmental, paleoclimate, and paleotectonic reconstructions, as well as geological studies of solid minerals and oil and gas deposits. Geochronological methods such as zircon U-Pb isotopes and apatite fission track dating are widely used. U-Pb isotope geochronology of carbonate minerals has made significant progress in recent years, and laser U-Pb dating has demonstrated excellent results in numerous geological cases.

[0005] Standard samples are essential for quality control in isotope geochemical analysis and are in short supply in all laboratories. Developing high-quality standards is a hallmark of laboratory performance and crucial for ensuring data reliability. Currently, a series of calcite standards for laser U-Pb dating spans various ages, including old, medium, and new. However, reliable standards for dolomite, a predominant mineral in ancient strata, are still lacking, necessitating the development of newer ones.

[0006] There are two difficulties in developing dolomite standards. On the one hand, the standard must be pure, with U content and U-Pb age matching those of the unknown sample, a stable isotope measurement signal, and consistent and stable U-Pb ages (not too many phases). On the other hand, dolomite has a complex origin, and multiple phases are difficult to distinguish at the microscopic scale, making it impossible to meet the above requirements. Therefore, no one has yet successfully developed a reliable dolomite standard.

[0007] Traditionally, the development of standards requires isotope dilution calibration, but 233 U- 205 Pb diluent is extremely rare and precious. Currently, only WC-1 and ASH-15 standards have their recommended ages calibrated with isotope diluent. Very few laboratories in the world use 233 U- 205Pb diluents are primarily used for U-Pb dating of carbonate minerals, either for standard development or for calibration with proven WC-1 and ASH-15 standards. However, reliable dolomite standards are currently unavailable, and the suitability of calcite standards for dolomite is questionable due to matrix effects.

[0008] Therefore, it is necessary to innovate the process and develop dolomite standard samples.

[0009] Summary of the Invention

[0010] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for developing a dolomite standard sample for calibrating by age method, a dolomite standard sample and its application, so as to solve the problem that traditional standard sample development cannot avoid the use of isotope diluent.

[0011] To achieve the above object, the present invention provides a method for developing a dolomite standard sample calibrated by an age method, which comprises:

[0012] Provide candidate dolomite standard samples;

[0013] Provide calcite, zircon and garnet standards that have been verified for matrix effects;

[0014] Using a calcite standard sample as a primary standard sample, and zircon and garnet standard samples as secondary standards, the age of the dolomite candidate standard sample is tested twice, and the test results are recorded as A and B respectively;

[0015] When A and B satisfy (AB) / B×100≤3, the dolomite candidate standard sample is used as the dolomite standard sample;

[0016] Wherein, the matrix effect verification includes:

[0017] Using any two of the calcite standard sample, the zircon standard sample, and the garnet standard sample as test sample C and test sample D, respectively, and the remaining third sample as the tested sample;

[0018] The age of the tested sample is tested using the test sample C and the test sample D, respectively. The test results are recorded as C1 and D1, respectively. The true age of the tested sample is recorded as E. When C1, D1, and E satisfy (C1-E) / E×100≤3 or (D1-E) / E×100≤3, the matrix effect verification is considered complete.

[0019] In the present invention, preferably, the selected calcite standard sample, zircon standard sample and garnet standard sample have U contents of the same order of magnitude as the dolomite candidate standard sample.

[0020] Using the calcite standard as the main standard and the zircon and garnet standards as the secondary standards, the age of the dolomite candidate standard can be tested more than twice. As the number of tests increases, the results will become more reliable. However, based on the method of the present invention, two measurements are sufficient.

[0021] According to the development method of the present invention, zircon and garnet with very large differences in mineral composition and structural component were selected, and calcite with good similarity (that is, similarity in U content, preferably, U content is of the same order of magnitude) to dolomite mineral composition and structural component was used, and the matrix effect was verified by interactive monitoring calibration. That is, it can be concluded that zircon and garnet can be used for calibrating calcite. Therefore, it is easy to know that calcite, zircon and garnet can be used for calibrating dolomite.

[0022] Through the above method, not only the possible matrix effect between calcite and dolomite is avoided, but also the problem of scarcity of diluents and existing standards is overcome, and a standard development process that is free from diluents and existing standards is established. This technical process is applicable to the development of other standards without existing standards and diluents.

[0023] According to a specific embodiment of the present invention, preferably, the method for testing the dolomite candidate standard sample is a laser method;

[0024] Preferably, the parameters of the laser beam in the laser method are wavelength 60-100 microns, frequency 5-15 Hz, energy density 2-5 J / cm 2 .

[0025] According to a specific embodiment of the present invention, preferably, before the laser method test, the test instrument is calibrated using NIST-612; preferably, the parameters of the test instrument are adjusted so that the 232Th / 238U ratio of NIST-612 is close to 1.

[0026] According to a specific embodiment of the present invention, preferably, the laser method test is completed using the Energy mode of iCap-RQ (inductively coupled plasma mass spectrometer).

[0027] According to a specific embodiment of the present invention, preferably, the method for selecting the dolomite candidate standard sample includes:

[0028] A potential dolomite standard sample is provided, and a geochemical analysis is performed on the potential dolomite standard sample to determine its diagenetic modification intensity. When the diagenetic modification intensity satisfies the conditions that no ring zoning structure is visible to the naked eye under cathodoluminescence and trace rare earth element scanning of the dolomite crystal, the Mn / Sr ratio is less than 1, and the error of the strontium isotope ratio obtained by three parallel sample measurements is less than 0.00001, the potential dolomite standard sample is used as the candidate dolomite standard sample.

[0029] Potential dolomite standard samples are required to have pure and uniform texture, stable isotope measurement signals, and small U-Pb age error (no more than 3%).

[0030] The present invention has no particular limitation on the specific production location of the dolomite.

[0031] According to a specific embodiment of the present invention, preferably, the geochemical analysis includes one or a combination of two or more of cathodoluminescence analysis, trace rare earth element surface scanning analysis, carbon, oxygen and strontium isotope analysis, and trace element content analysis.

[0032] According to a specific embodiment of the present invention, preferably, the development method further comprises: reliability verification;

[0033] Preferably, the reliability verification method includes:

[0034] The dolomite standard sample is used to test the age of a standard sample with a similar U content (same order of magnitude), and the test result is recorded as F. The true age of the similar standard sample is recorded as G. When F and G satisfy (FG) / G×1000≤3, the dolomite standard sample is used as a reliable standard sample; wherein the similar standard sample is selected from one of garnet, zircon, and calcite.

[0035] Through the above reliability verification, the reliability of the dolomite standard sample of the present invention can be further confirmed.

[0036] According to a specific embodiment of the present invention, preferably, the calcite standard sample is selected from WC-1 calcite or ASH15 calcite.

[0037] According to a specific embodiment of the present invention, preferably, the zircon standard is selected from 91500 zircon or Temora zircon.

[0038] According to a specific embodiment of the present invention, preferably, the garnet standard sample is selected from TC garnet.

[0039] According to another aspect of the present invention, a dolomite standard sample obtained according to the above development method is also provided.

[0040] According to another aspect of the present invention, a method for using the aforementioned dolomite standard in the development of U-Pb isotope dating technology is also provided. The invention can be applied to provide standard sample support for the development and application of laser and solution-based dolomite U-Pb isotope dating techniques. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG1 is a flow chart of the method for developing a dolomite standard sample for calibrating the age method according to the present invention.

[0042] Figure 2 shows the measured age of zircon sample 91500.

[0043] Figure 3 shows the age of the calcite standard sample AHX-1D measured using the zircon standard sample as the normalized value.

[0044] Figure 4 shows the age of garnet standard sample TC-13 measured using zircon standard sample as the normalized value.

[0045] Figure 5 shows the age of garnet standard sample QC-04 measured using zircon standard sample as the normalized value.

[0046] Figure 6 shows the measured age of calcite standard sample AHX-1D.

[0047] Figure 7 shows the age of the zircon standard sample 91500, normalized by the calcite standard sample.

[0048] Figure 8 shows the age of garnet standard sample TC-13 measured using the calcite standard sample as the normalized value.

[0049] Figure 9 shows the age of the dolomite candidate standard sample GT2-1 obtained by the first calculation using the calcite standard sample as the normalized value.

[0050] Figure 10 shows the age of the dolomite candidate standard sample GT2-1 obtained by the second calculation using the calcite standard sample as the normalized value. DETAILED DESCRIPTION

[0051] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0052] Example 1

[0053] A method for developing a dolomite standard sample for calibrating the age method is shown in the flow chart in FIG1 , and includes the following steps:

[0054] Acquisition of potential S100 dolomite standard samples

[0055] The potential standard samples collected were first analyzed by cathodoluminescence and trace rare earth element surface scanning, as well as carbon, oxygen, strontium isotopes and trace element content. Based on the oxygen isotope, strontium isotope, strontium content, and cathodoluminescence and rare earth element surface scanning characteristics, it was determined that the dolomite diagenetic transformation intensity was relatively weak. That is, the dolomite crystals had no obvious ring zoning structure under cathodoluminescence and trace rare earth element surface scanning, the Mn / Sr ratio was less than 1, and the error of the strontium isotope ratio obtained from three parallel samples was less than 0.00001; therefore, it can be used as a candidate standard sample.

[0056] Verification of S200 matrix effect

[0057] First, zircon standards with very different mineral and structural components but similar U content were selected as monitoring standards to test the ages of existing calcite and garnet standards. Specifically, the age of the standards was tested using laser ablation inductively coupled plasma mass spectrometry.

[0058] As shown in Figure 2, the measured age of zircon sample 91500 is 1062.4±0.4Ma;

[0059] As shown in Figure 3, using zircon standards as the normalized value, the age of the calcite standard sample AHX-1D was measured to be 240.0±1.2Ma, which is very close to its true age of 236.9±1.6Ma;

[0060] As shown in Figure 4, the age of the garnet standard sample TC-13 was measured using the zircon standard as the normalized value, which is 125.20±0.56Ma, very close to its true age of 126.2±2.3Ma.

[0061] As shown in Figure 5, the age of the garnet standard sample QC-04 was measured using the zircon standard as the normalized value, which is 129.34±0.39Ma, very close to its true age of 130±1Ma.

[0062] Then, the ages of zircon and garnet samples were calculated using the age of the calcite sample as the normalized value.

[0063] As shown in Figure 6, the measured age of the calcite standard sample AHX-1D is 236.87±0.82Ma;

[0064] As shown in Figure 7 , the calcite standard is used as the normalized value, and the age of the zircon standard sample 91500 is measured to be 1067.7±2.4Ma, which is very close to its true age value;

[0065] As shown in Figure 8, the calcite standard is used as the normalized value, and the age of the garnet standard TC-3 is measured to be 126.77±0.52Ma, which is very close to its true age of 126.2±2.3Ma;

[0066] Through interactive monitoring calibration, zircon and garnet, which have very different mineral compositions and structural components, gave age results that were close enough to the true values ​​compared to calcite. It can be concluded that zircon and garnet can be used to calibrate calcite. Since calcite and dolomite have better similarities in mineral compositions and structural components, it is easy to conclude that calcite, zircon and garnet can also be used to calibrate dolomite.

[0067] S300 is based on the determination of dolomite standards using calcite standards

[0068] According to the verification results of the above base effect, the calcite standard sample can be used as the standardized value to carry out the determination of the dolomite standard sample.

[0069] Specifically, an AHX-1D calcite standard, which may have a similar age to the candidate dolomite standard, was selected as the primary standard, and 91500 zircon and garnet were used as secondary standards. Using NIST-612, the instrument parameters were optimized to a NIST 232Th / 238U ratio close to 1. Then, using an 80-micron laser beam, 10 Hz, and 6.60 mJ energy, the dolomite candidate standard was measured twice on the iCap-RQ using Energymode.

[0070] For samples older than 100 million years, the age difference is considered to be close if it does not exceed 30 million years. If the measurement results show that the ages of dolomite and calcite are not similar, it is necessary to select a calcite standard sample with a similar age and re-measure it.

[0071] As shown in Figure 9 , the calcite standard is the standardized value, and the age of the dolomite candidate standard sample GT2-1 calculated for the first time is 253.8±2.2Ma;

[0072] As shown in Figure 10 , the calcite standard sample is the standardized value, and the age of the dolomite candidate standard sample GT2-1 calculated for the second time is 248.1±2.6Ma;

[0073] (253.8-248.1) / 253.8×100=2.24. It can be seen that the ages of the two dolomite candidate standard samples are close enough to meet the conditions for being used as standard samples.

[0074] Test method:

[0075] Laser carbon and oxygen isotope measurements are performed using the LA-IRMS. The laser equipment (LA) consists of an Nd:YAG (yttrium aluminum garnet) near-infrared laser, a cooling system, a microscopic imaging system, and a gas transport and separation system. The Nd:YAG laser outputs a near-infrared coherent laser beam with a wavelength of 1064 nm and a spot size of less than 20 μm. A krypton lamp is used as the pump energy source for the Nd:YAG laser. The operating current is 7-20 A, generating an output energy of 7 to 40 W, and the sample penetration depth is 30-50 μm. The stable gas isotope instrument is a Detla V Advantage. Helium is used as the carrier gas during the laser ablation process. The laser reacts with carbonates to generate CO2 gas, which is then separated and purified to obtain pure CO2 gas for analysis by the isotope mass spectrometer. The laser beam spot and current used in this analysis were 20 μm and 14-20 A, respectively. The laser used continuous wave (CW) output. Data were calibrated using the national standard GBW04405 and the laboratory's in-house standard 811. Data were processed using Thermo Fisher Scientific software ISODAT 3.0 and presented in PDB format. The δ13C and δ18O measurements were accurate to ±0.1‰ and ±0.2‰, respectively. The laser beam diameter was 500 μm. Only the cores of fine-grained and medium-coarse-grained dolomite were analyzed. Residual shadows of recognizable original grains and cement within some coarse-grained dolomite were also examined. For comparison, dolomite crystals and calcite cement within limestone were also tested.

[0076] Strontium isotope analysis was performed using a solid-state mass spectrometer and an IVP-MS (X Series II). 100–150 mg of powdered sample was dissolved in a 1:1 mixture of HNO₃ and HF at 190°C for 48 hours. Strontium isotopes were extracted and analyzed using conventional procedures (Baadsgard, 1987). The standard sample was NBS987. The average error of the 87Sr / 86Sr ratio was ±0.5 × 10 -5 .

[0077] Trace rare earth elements were analyzed using whole-rock powder samples using an inductively coupled plasma mass spectrometer (ICP-MS) using a Thermo Fisher iCAP RQ autosampler and a CETAC 560. 50–100 mg of powder sample was dissolved in a mixture of 0.6 mL of HNO₃ and 2.5 mL of HF at 185°C for 72 hours. After drying, the sample was reacted with 4 mL of a 20% mixed acid solution (HCl:HNO₃ = 4:1) at 130°C for 3 hours. After removal of the acid, the dissolved sample was analyzed using standard procedures in an ICP-MS. The standard sample used was USGS W-2a, and the solution contained four internal standards: Rh, In, Re, and Bi. The measurement precision was 0.1 ppb, with an error of ±5%.

[0078] Cathodoluminescence was performed using CL8200MK5 produced by CITL, and the implementation standard was SY / T5916-2013 “Cathode Luminescence Identification Method for Rocks and Minerals”.

[0079] LA-ICP-MS micro-area in situ laser scanning is used to perform micro-area imaging of a selected area. First, the element type and integration time are selected. Next, the scanning area, laser beam spot, energy density, movement speed, ablation frequency, and scanning line spacing are set based on the sample's mineralogy. LA-ICP-MS micro-area in situ laser scanning imaging is then tested on the machine. The data is then processed and imaged using the Iolite software.

[0080] As can be seen from the examples, the method developed in the present invention can successfully develop and obtain dolomite standard samples.

Claims

1. A method for developing a dolomite standard sample calibrated by age method, characterized in that: include: Provide candidate dolomite standards; Provide calcite, zircon and garnet standards with matrix effect verified; Using the calcite standard sample as the main standard sample, and the zircon standard sample and the garnet standard sample as the secondary standard samples, the age of the dolomite candidate standard sample is tested twice, and the obtained test results are recorded as A and B respectively; When A and B satisfy (AB) / B×100≤3, the dolomite candidate standard sample is used as the dolomite standard sample.

2. The development method according to claim 1, characterized in that: The method for testing the dolomite candidate standard sample is a laser method.

3. The development method according to claim 2, characterized in that: The parameters of the laser beam in the laser method are wavelength 60-100 microns, frequency 5-15 Hz, energy density 2-5 J / cm 2 .

4. The development method according to claim 2, characterized in that: Prior to the laser method test, the test instrument was calibrated using NIST-612.

5. The development method according to claim 4, characterized in that: The parameters of the test instrument were adjusted so that the 232Th / 238U ratio of NIST-612 was close to 1.

6. The development method according to claim 5, characterized in that: The laser method test was performed using the Energy mode of iCap-RQ.

7. The development method according to claim 1, characterized in that: The method for selecting the dolomite candidate standard sample comprises: A dolomite potential standard sample is provided, and a geochemical analysis is performed on the dolomite potential standard sample to determine its diagenetic transformation intensity. When the diagenetic transformation intensity satisfies that the dolomite crystal has no obvious ring-zone structure under cathode luminescence and trace rare earth element surface scanning, Mn / Sr is less than 1, and the strontium isotope ratio error obtained by measuring three parallel samples is less than 0.00001, the dolomite potential standard sample is used as the dolomite candidate standard sample.

8. The development method according to claim 7, characterized in that: The geochemical analysis includes one or a combination of two or more of cathode luminescence analysis, trace rare earth element surface scanning analysis, carbon, oxygen and strontium isotope analysis, and trace element content analysis.

9. The development method according to claim 1, characterized in that: The development method also includes: Reliability verification.

10. The development method according to claim 9, characterized in that: The reliability verification method includes: The age of the similar standard sample is tested by the dolomite standard sample, and the test result is recorded as F, and the true age of the similar standard sample is recorded as G. When F and G satisfy (FG) / G×100≤3, the dolomite standard sample is used as a reliable standard. Sample; wherein the similar standard sample is selected from one of garnet or zircon.

11. The development method according to claim 1, characterized in that: The calcite standard sample is selected from WC-1 calcite or ASH15 calcite.

12. The development method according to claim 1, characterized in that: The zircon standard sample is selected from 91500 zircon or Temora zircon.

13. The development method according to claim 1, characterized in that: The garnet standard sample is selected from TC garnet.

14. A dolomite standard sample obtained by the development method according to any one of claims 1 to 13.

15. Use of the dolomite standard sample according to claim 14 in the development of U-Pb isotope dating technology.

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