Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay
The fluids in of pegmatite rare metal deposits are generally rich in rare metal elements and volatiles (B, P, F, H<sub>2</sub>O, CO<sub>2</sub>, etc.), and they have a high capacity for dissolving and migrating rare metals. The Dakalasu No. 1 rare metal pegmatite vein is loca...
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MDPI AG
2023-03-01
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| Online Access: | https://www.mdpi.com/2075-163X/13/3/365 |
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| author | Jiehao Zhou Hui Zhang Yong Tang Zhenghang Lv Shenjin Guan |
| author_facet | Jiehao Zhou Hui Zhang Yong Tang Zhenghang Lv Shenjin Guan |
| author_sort | Jiehao Zhou |
| collection | DOAJ |
| description | The fluids in of pegmatite rare metal deposits are generally rich in rare metal elements and volatiles (B, P, F, H<sub>2</sub>O, CO<sub>2</sub>, etc.), and they have a high capacity for dissolving and migrating rare metals. The Dakalasu No. 1 rare metal pegmatite vein is located in northwest China’s Altay orogenic belt. Previous studies have indicated that it is a small- to medium-sized beryllium-niobium-tantalum deposit. It showed significant mineral assemblage zonations from the rim to the core, and the mineralizing fluids define a volatile-rich NaCl-H<sub>2</sub>O-CO<sub>2</sub> ± CH<sub>4</sub> system. In this contribution, beryl and quartz, which are widely developed in each mineral association and textural zone, were selected for fluid inclusion research through detailed petrographic investigation, microthermometry, and LA-ICP-MS analysis. Petrographic results show that at least three types of fluid inclusions are developed in each mineral textural zone. They are CO<sub>2</sub>-rich inclusions (type I), gas-liquid two-phase inclusions (type II), and daughter mineral-bearing inclusions (type III), respectively. Additionally, minor melt inclusions (type IV) are visible in the beryl from the rim zone. Microthermometric measurements showed that the homogenization temperature of fluid inclusions in the rim zone was concentrated between 242 °C and 293 °C, with an average of 267 °C, and the salinity was between 7.2–10.3 wt% NaCl<sub>eqv</sub>, with an average of 8.6 wt% NaCl<sub>eqv</sub>. In comparison, the temperature of the core zone was in the range of 225–278 °C, with an average of 246 °C, and the salinity focused between 6.0–7.7 wt% NaCl<sub>eqv</sub>, with an average of 7.1 wt% NaCl<sub>eqv</sub>. The quantitative analysis of individual inclusions by LA-ICP-MS revealed that Li, B, K, Zn, Rb, Sb, Cs, and As were relatively enriched in the rim zone. In contrast, the core zone showed a decreasing trend in trace elements such as Li, B, K, Rb, and Cs. The CO<sub>2</sub> content in the fluid exhibited the same decreasing trend from the rim to the core zone, indicating that volatile components such as CO<sub>2</sub> played an essential role in the migration and enrichment of rare metal elements. The melt-fluid immiscibility is likely to be a necessary mechanism for significantly enriching rare metals in the Dakalasu No. 1 pegmatite dyke. |
| first_indexed | 2024-03-11T06:09:22Z |
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| spelling | doaj.art-7c5b70dc2242463fb711912a57490aad2023-11-17T12:47:35ZengMDPI AGMinerals2075-163X2023-03-0113336510.3390/min13030365Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, AltayJiehao Zhou0Hui Zhang1Yong Tang2Zhenghang Lv3Shenjin Guan4Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650031, ChinaKey Laboratory of High-Temperature and High-Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy Sciences, Guiyang 550081, ChinaKey Laboratory of High-Temperature and High-Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy Sciences, Guiyang 550081, ChinaKey Laboratory of High-Temperature and High-Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy Sciences, Guiyang 550081, ChinaFaculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650031, ChinaThe fluids in of pegmatite rare metal deposits are generally rich in rare metal elements and volatiles (B, P, F, H<sub>2</sub>O, CO<sub>2</sub>, etc.), and they have a high capacity for dissolving and migrating rare metals. The Dakalasu No. 1 rare metal pegmatite vein is located in northwest China’s Altay orogenic belt. Previous studies have indicated that it is a small- to medium-sized beryllium-niobium-tantalum deposit. It showed significant mineral assemblage zonations from the rim to the core, and the mineralizing fluids define a volatile-rich NaCl-H<sub>2</sub>O-CO<sub>2</sub> ± CH<sub>4</sub> system. In this contribution, beryl and quartz, which are widely developed in each mineral association and textural zone, were selected for fluid inclusion research through detailed petrographic investigation, microthermometry, and LA-ICP-MS analysis. Petrographic results show that at least three types of fluid inclusions are developed in each mineral textural zone. They are CO<sub>2</sub>-rich inclusions (type I), gas-liquid two-phase inclusions (type II), and daughter mineral-bearing inclusions (type III), respectively. Additionally, minor melt inclusions (type IV) are visible in the beryl from the rim zone. Microthermometric measurements showed that the homogenization temperature of fluid inclusions in the rim zone was concentrated between 242 °C and 293 °C, with an average of 267 °C, and the salinity was between 7.2–10.3 wt% NaCl<sub>eqv</sub>, with an average of 8.6 wt% NaCl<sub>eqv</sub>. In comparison, the temperature of the core zone was in the range of 225–278 °C, with an average of 246 °C, and the salinity focused between 6.0–7.7 wt% NaCl<sub>eqv</sub>, with an average of 7.1 wt% NaCl<sub>eqv</sub>. The quantitative analysis of individual inclusions by LA-ICP-MS revealed that Li, B, K, Zn, Rb, Sb, Cs, and As were relatively enriched in the rim zone. In contrast, the core zone showed a decreasing trend in trace elements such as Li, B, K, Rb, and Cs. The CO<sub>2</sub> content in the fluid exhibited the same decreasing trend from the rim to the core zone, indicating that volatile components such as CO<sub>2</sub> played an essential role in the migration and enrichment of rare metal elements. The melt-fluid immiscibility is likely to be a necessary mechanism for significantly enriching rare metals in the Dakalasu No. 1 pegmatite dyke.https://www.mdpi.com/2075-163X/13/3/365CO<sub>2</sub>-rich fluidLA-ICP-MSenrichment mechanismpegmatite-type rare metal depositsDakalasuAltay |
| spellingShingle | Jiehao Zhou Hui Zhang Yong Tang Zhenghang Lv Shenjin Guan Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay Minerals CO<sub>2</sub>-rich fluid LA-ICP-MS enrichment mechanism pegmatite-type rare metal deposits Dakalasu Altay |
| title | Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay |
| title_full | Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay |
| title_fullStr | Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay |
| title_full_unstemmed | Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay |
| title_short | Characteristics and Geological Significance of CO<sub>2</sub>-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay |
| title_sort | characteristics and geological significance of co sub 2 sub rich fluid inclusions in dakalasu no 1 pegmatite dyke altay |
| topic | CO<sub>2</sub>-rich fluid LA-ICP-MS enrichment mechanism pegmatite-type rare metal deposits Dakalasu Altay |
| url | https://www.mdpi.com/2075-163X/13/3/365 |
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