Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards
© 2016 by the authors; licensee MDPI, Basel, Switzerland.U-Pb dating of the common iron-oxide hematite (a-Fe2O3), using laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS), provides unparalleled insight into the timing and processes of mineral deposit formation. Until now, the fu...
| Main Authors: | , , , , , , , |
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| Format: | Journal Article |
| Published: |
2016
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| Online Access: | http://hdl.handle.net/20.500.11937/52390 |
| _version_ | 1848758915966173184 |
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| author | Courtney-Davies, L. Zhu, Z. Ciobanu, C. Wade, B. Cook, N. Ehrig, K. Cabral, A. Kennedy, Allen |
| author_facet | Courtney-Davies, L. Zhu, Z. Ciobanu, C. Wade, B. Cook, N. Ehrig, K. Cabral, A. Kennedy, Allen |
| author_sort | Courtney-Davies, L. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | © 2016 by the authors; licensee MDPI, Basel, Switzerland.U-Pb dating of the common iron-oxide hematite (a-Fe2O3), using laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS), provides unparalleled insight into the timing and processes of mineral deposit formation. Until now, the full potential of this method has been negatively impacted by the lack of suitable matrix-matched standards. To achieve matrix-matching, we report an approach in which a U-Pb solution and ablated material from 99.99% synthetic hematite are simultaneously mixed in a nebulizer chamber and introduced to the ICP-MS. The standard solution contains fixed U- and Pb-isotope ratios, calibrated independently, and aspiration of the isotopically homogeneous solution negates the need for a matrix-matched, isotopically homogenous natural iron-oxide standard. An additional advantage of using the solution is that the individual U-Pb concentrations and isotope ratios can be adjusted to approximate that in the unknown, making the method efficient for dating hematite containing low (~10 ppm) to high (>1 wt %) U concentrations. The above-mentioned advantage to this solution method results in reliable datasets, with arguably-better accuracy in measuring U-Pb ratios than using GJ-1 Zircon as the primary standard, which cannot be employed for such low U concentrations. Statistical overlaps between 207Pb/206Pb weighted average ages (using GJ-1 Zircon) and U-Pb upper intercept ages (using the U-Pb mixed solution method) of two samples from iron-oxide copper-gold (IOCG) deposits in South Australia demonstrate that, although fractionation associated with a non-matrix matched standard does occur when using GJ-1 Zircon as the primary standard, it does not impact the 207Pb/206Pb or upper intercept age. Thus, GJ-1 Zircon can be considered reliable for dating hematite using LA-ICP-MS. Downhole fractionation of 206Pb/238U is observed to occur in spot analyses of hematite. The use of rasters in future studies will hopefully minimize this problem, allowing for matrix-matched data. Using the mixed-solution method in this study, we have validated a published hematite Pb-Pb age for Olympic Dam, and provide a new age (1604 ± 11 Ma) for a second deposit in the same province. These ages are further evidence that the IOCG mineralizing event is tied to large igneous province (LIP) magmatism in the region at ~1.6 Ga. |
| first_indexed | 2025-11-14T09:51:35Z |
| format | Journal Article |
| id | curtin-20.500.11937-52390 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T09:51:35Z |
| publishDate | 2016 |
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| spelling | curtin-20.500.11937-523902017-09-13T15:39:43Z Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards Courtney-Davies, L. Zhu, Z. Ciobanu, C. Wade, B. Cook, N. Ehrig, K. Cabral, A. Kennedy, Allen © 2016 by the authors; licensee MDPI, Basel, Switzerland.U-Pb dating of the common iron-oxide hematite (a-Fe2O3), using laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS), provides unparalleled insight into the timing and processes of mineral deposit formation. Until now, the full potential of this method has been negatively impacted by the lack of suitable matrix-matched standards. To achieve matrix-matching, we report an approach in which a U-Pb solution and ablated material from 99.99% synthetic hematite are simultaneously mixed in a nebulizer chamber and introduced to the ICP-MS. The standard solution contains fixed U- and Pb-isotope ratios, calibrated independently, and aspiration of the isotopically homogeneous solution negates the need for a matrix-matched, isotopically homogenous natural iron-oxide standard. An additional advantage of using the solution is that the individual U-Pb concentrations and isotope ratios can be adjusted to approximate that in the unknown, making the method efficient for dating hematite containing low (~10 ppm) to high (>1 wt %) U concentrations. The above-mentioned advantage to this solution method results in reliable datasets, with arguably-better accuracy in measuring U-Pb ratios than using GJ-1 Zircon as the primary standard, which cannot be employed for such low U concentrations. Statistical overlaps between 207Pb/206Pb weighted average ages (using GJ-1 Zircon) and U-Pb upper intercept ages (using the U-Pb mixed solution method) of two samples from iron-oxide copper-gold (IOCG) deposits in South Australia demonstrate that, although fractionation associated with a non-matrix matched standard does occur when using GJ-1 Zircon as the primary standard, it does not impact the 207Pb/206Pb or upper intercept age. Thus, GJ-1 Zircon can be considered reliable for dating hematite using LA-ICP-MS. Downhole fractionation of 206Pb/238U is observed to occur in spot analyses of hematite. The use of rasters in future studies will hopefully minimize this problem, allowing for matrix-matched data. Using the mixed-solution method in this study, we have validated a published hematite Pb-Pb age for Olympic Dam, and provide a new age (1604 ± 11 Ma) for a second deposit in the same province. These ages are further evidence that the IOCG mineralizing event is tied to large igneous province (LIP) magmatism in the region at ~1.6 Ga. 2016 Journal Article http://hdl.handle.net/20.500.11937/52390 10.3390/min6030085 unknown |
| spellingShingle | Courtney-Davies, L. Zhu, Z. Ciobanu, C. Wade, B. Cook, N. Ehrig, K. Cabral, A. Kennedy, Allen Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards |
| title | Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards |
| title_full | Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards |
| title_fullStr | Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards |
| title_full_unstemmed | Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards |
| title_short | Matrix-matched iron-oxide laser ablation ICP-MS U-Pb geochronology using mixed solution standards |
| title_sort | matrix-matched iron-oxide laser ablation icp-ms u-pb geochronology using mixed solution standards |
| url | http://hdl.handle.net/20.500.11937/52390 |