Raman Spectroscopy for Characterization of Peridotite Paragenesis Mineral Inclusions in Diamonds
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-09-08 |
| Journal | LITHOSPHERE (Russia) |
| Authors | A. D. Kalugina, D. A. Zedgenizov, A. M. Logvinova |
| Institutions | Ural State Mining University, Zavaritsky Institute of Geology and Geochemistry |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research establishes a non-destructive, quantitative methodology using Raman spectroscopy for in situ chemical analysis of peridotite paragenesis mineral inclusions (olivine, orthopyroxene, clinopyroxene, and garnet) within natural diamonds.
- Core Value Proposition: Provides a rapid, non-destructive method to assess the chemical composition of mantle minerals trapped in diamonds, crucial for understanding mantle geology and diamond exploration.
- Quantitative Analysis: Developed robust linear regression models (Deming regression) correlating specific Raman peak shifts (cm-1) with the content of major chemical components (e.g., CaO, MgO, Na2O, Al2O3, Cr2O3) in clinopyroxene and garnet.
- Isomorphism Confirmation: Characteristic shifts in Raman modes confirmed key isomorphic substitutions: Forsterite-Fayalite (Mg-Fe) in olivine, Enstatite-Ferrosilite (Mg-Fe) in orthopyroxene, Diopside-Jadeite (CaMg-NaAl) in clinopyroxene, and Al-Cr/Ca-Mg in garnet.
- High Accuracy: Quantitative results for clinopyroxene components showed good agreement with Electron Probe Micro-Analysis (EPMA) data, with modal errors typically low (e.g., CaO <1.1 wt %, Na2O <0.4 wt %).
- Geological Utility: The method allows for the confident differentiation of clinopyroxene and garnet inclusions belonging to different mantle parageneses (e.g., harzburgite, lherzolite, websterite) based solely on spectroscopic data.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the key experimental and performance parameters derived from the study of mineral inclusions.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Raman Spectrometer | LabRAMHR800 | N/A | Instrument used for spectral acquisition. |
| Excitation Laser | Nd:YAG | N/A | Laser type used. |
| Wavelength | 532 | nm | Laser wavelength. |
| Laser Power | 10 | mW | Power used on the sample. |
| Spectral Range | 100-1200 | cm-1 | Range of recorded Raman shifts. |
| Grating Density | 1800 | lines/mm | Diffraction grating specification. |
| Peak Position Precision | Âą0.5 | cm-1 | Precision achieved via Lorentz function fitting. |
| Olivine Mg# Range Studied | 0.900-0.935 | N/A | Compositional range of peridotite olivine inclusions. |
| Cpx CaO Regression Error | 1.1 (Modal) | wt % | Error relative to EPMA data (for CaO <5 wt %). |
| Cpx Na2O Regression Error | 0.4 (Modal) | wt % | Error relative to EPMA data (for Na2O <2.5 wt %). |
| Garnet Ca/Mg Regression Error | <12 | % component | Maximum total error for Ca and Mg determination using V1 shift. |
| Garnet Cr/Al Regression Error | <0.3 | f.u. | Error for Cr and Al determination using V2 shift (formula units). |
Key Methodologies
Section titled âKey MethodologiesâThe study combined high-precision chemical analysis with non-destructive Raman spectroscopy, focusing on correlating chemical composition with characteristic vibrational mode shifts.
- Sample Selection and Preparation: Diamonds containing peridotite paragenesis inclusions (olivine, Opx, Cpx, Garnet) from the Yakutian province were selected. Samples were polished along the (110) plane to expose inclusions for EPMA and Raman analysis.
- Reference Chemical Analysis (EPMA): Chemical compositions of exposed inclusions were determined using a JEOL JXA-8100 EPMA (20 keV accelerating voltage, 100 nA beam current) to provide calibration data (wt%).
- Raman Spectroscopy Acquisition: Raman spectra were obtained using a LabRAMHR800 spectrometer equipped with a 532 nm Nd:YAG laser (10 mW power). Accumulation times were 7-10 seconds over 10-15 cycles.
- Anisotropy and Stress Assessment: For anisotropic minerals (olivine, Opx, Cpx), the sample was rotated in 15° steps to assess the influence of crystallographic orientation on mode intensity and position. Residual stress effects were evaluated by comparing spectra before and after opening the inclusions.
- Data Processing and Peak Fitting: Spectra were processed using OPUS 8.2. Peak positions were precisely determined by fitting the curves with the Lorentz function, ensuring high accuracy (Âą0.5 cm-1).
- Quantitative Model Development: Deming regression lines were calculated to establish linear relationships between the shift of key Raman modes (e.g., Cpx Si-Obr V11, Garnet V1/V3) and the concentration of major elements (e.g., CaO, Na2O, MgO, Al2O3, Cr2O3) determined by EPMA.
- System of Equations (Garnet): For quantitative Ca and Mg determination in garnet, a system of two linear equations was established, linking the V1 or V3 peak shift to Ca and Mg content, constrained by the assumption that Ca + Mg + Fe = 3 formula units.
Commercial Applications
Section titled âCommercial ApplicationsâThis non-destructive spectroscopic methodology has significant implications for geological research and commercial diamond exploration.
- Diamond Exploration and Kimberlite Assessment:
- Rapid, non-destructive screening of indicator minerals (garnet and clinopyroxene xenocrysts) found in kimberlite pipes.
- Using Raman-derived chemical data (especially Cr and Ca content in garnet) to classify mantle paragenesis (G10 harzburgite, G9 lherzolite) and assess the diamond potential of a kimberlite source.
- Mantle Geochemistry and Thermobarometry:
- Providing in situ chemical data for Cpx and Grt inclusions, which are essential inputs for calculating the pressure and temperature (P-T) conditions of the lithospheric mantle during diamond formation.
- Mapping the chemical heterogeneity and thermal regime of the subcontinental lithospheric mantle.
- High-Value Diamond Certification:
- Non-destructive identification and chemical characterization of mineral inclusions in high-value natural diamonds, confirming their mantle origin and paragenesis without damaging the stone.
- Mineralogical Research:
- Rapid identification and compositional estimation of silicate solid solutions (olivine, pyroxenes, garnet) in geological samples where traditional microprobe analysis is impractical or destructive.
View Original Abstract
Research subject . Spectroscopic features (Raman spectra) of mineral inclusions of peridotite paragenesis (olivine, orthopyroxene, clinopyroxene, garnet) in natural diamonds of the Yakutian diamondiferous province. Materials and methods . A series of diamonds was studied both with single mineral inclusions and with associations of inclusions of peridotite paragenesis. The chemical composition of mineral inclusions in diamonds was determined using an electron probe micro-analyzer (EPMA). The Raman spectra of inclusions were obtained on a spectrometer equipped with a Nd:YAG laser with a wavelength of 532 nm. Results . The revealed spectroscopic characteristics of mineral inclusions in natural diamonds reflect specific features of their chemical composition. Thus, the shift in the positions of the Raman peaks DB1 and DB2 in the olivine spectra reflects the forsterite - fayalite (Mg-Fe) isomorphism; changes in the positions of valence vibrational modes in the Raman spectra of clinopyroxene Si-O nbr (ν 16 ) and Si-O br (ν 11 ) and orthopyroxene (ν 17 ) reflect the isomorphism of diopside - jadeite (CaMg-NaAl) and enstatite - ferrosilite (Mg-Fe), position shifts of deformation (ν 2 ) and valence (ν 1 , ν 3 ) modes of vibrational energies of the Si-O bond in garnets reflect the Al-Cr and Ca-Mg isomorphism, respectively. Conclusions . For the identified correlations, regression lines were calculated, which can be used to determine the quantitative contents of the main chemical components of mineral inclusions (clinopyroxene and garnet) of peridotite paragenesis in situ in diamonds. The developed method for evaluating the chemical composition of garnet and clinopyroxene inclusions can be used to distinguish clinopyroxene and garnet inclusions from different mantle parageneses.