Limits...
Lithium isotope traces magmatic fluid in a seafloor hydrothermal system.

Yang D, Hou Z, Zhao Y, Hou K, Yang Z, Tian S, Fu Q - Sci Rep (2015)

Bottom Line: The δ(7)Li results vary from +4.5‰ to +13.8‰ for fluid inclusions and from +6.7‰ to +21.0‰ for the hosted gangue quartz(9 gangue quartz samples containing primary fluid inclusions).This δ(7)Li range, together with Li-O modeling , suggest that magmatic fluid played a significant role in the ore formation.This study demonstrates that Li isotope can be effectively used to trace magmatic fluids in a seafloor hydrothermal system and has the potential to monitor fluid mixing and ore-forming process.

View Article: PubMed Central - PubMed

Affiliation: Institute of Mineral Resources, CAGS, Beijing 100037, P. R. China.

ABSTRACT
Lithium isotopic compositions of fluid inclusions and hosted gangue quartz from a giant volcanogenic massive sulfide deposit in China provide robust evidence for inputting of magmatic fluids into a Triassic submarine hydrothermal system. The δ(7)Li results vary from +4.5‰ to +13.8‰ for fluid inclusions and from +6.7‰ to +21.0‰ for the hosted gangue quartz(9 gangue quartz samples containing primary fluid inclusions). These data confirm the temperature-dependent Li isotopic fractionation between hydrothermal quartz and fluid (i.e., Δδ(7)Liquartz-fluid = -8.9382 × (1000/T) + 22.22(R(2) = 0.98; 175 °C-340 °C)), which suggests that the fluid inclusions are in equilibrium with their hosted quartz, thus allowing to determine the composition of the fluids by using δ(7)Liquartz data. Accordingly, we estimate that the ore-forming fluids have a δ(7)Li range from -0.7‰ to +18.4‰ at temperatures of 175-340 °C. This δ(7)Li range, together with Li-O modeling , suggest that magmatic fluid played a significant role in the ore formation. This study demonstrates that Li isotope can be effectively used to trace magmatic fluids in a seafloor hydrothermal system and has the potential to monitor fluid mixing and ore-forming process.

No MeSH data available.


Oxygen-lithium isotopic compositions of the ore-forming fluids at Gacun, which can be reproduced by mixing of variable amounts of seawater (δ18O = +0‰; δ7Li = +31.5‰) with a magmatic fluid (δ18O = +8‰; δ7Li = +1.5‰) with variable Limagmatic/Liseawater mass mixing ratios.Dot-lines with open-circles (10% interval) show a binary mixing between magmatic fluid and seawater. Lim/Lic refers Li concentration ratios in magmatic fluid and seawater. Modeling calculation sees Appendix II.
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f3: Oxygen-lithium isotopic compositions of the ore-forming fluids at Gacun, which can be reproduced by mixing of variable amounts of seawater (δ18O = +0‰; δ7Li = +31.5‰) with a magmatic fluid (δ18O = +8‰; δ7Li = +1.5‰) with variable Limagmatic/Liseawater mass mixing ratios.Dot-lines with open-circles (10% interval) show a binary mixing between magmatic fluid and seawater. Lim/Lic refers Li concentration ratios in magmatic fluid and seawater. Modeling calculation sees Appendix II.

Mentions: To date, a few experiments have been performed to determine the Li isotopic fractionation between magmatic fluids and melts3031. A theoretic model shows that the δ7Li of both residual melts and exsolving fluids do not change significantly with progressive fluid exsolution17. Based on Li isotopic compositions of the Gacun rhyolites (δ7Li: +1.0‰ to +2.3‰), we estimate that the δ7Li values of initial fluid exsolving from a rhyolitic melt vary from +1.0‰ to +3.0, close to the lowest measured δ7Li values for the LSO. This means that variation in δ7Lifluid (- 0.7 to +18.5‰) observed at Gacun may be caused by other processes, such as interacting with marine sediments (δ7Li = −1.0 ∼ +24‰)3233 and mixing with seawater (δ7Li = +31.5‰)2426. However, the lack of hydrothermal alteration in the hanging-wall (Triassic shales) and the absence of marine sediments in the host package at Gacun (Fig. 1) rule out the first possibility. All δ7Lifluid data may be interpreted by a binary mixing between magmatic fluid and seawater, which is supported by Li–O isotopic system at Gacun (Fig. 3).


Lithium isotope traces magmatic fluid in a seafloor hydrothermal system.

Yang D, Hou Z, Zhao Y, Hou K, Yang Z, Tian S, Fu Q - Sci Rep (2015)

Oxygen-lithium isotopic compositions of the ore-forming fluids at Gacun, which can be reproduced by mixing of variable amounts of seawater (δ18O = +0‰; δ7Li = +31.5‰) with a magmatic fluid (δ18O = +8‰; δ7Li = +1.5‰) with variable Limagmatic/Liseawater mass mixing ratios.Dot-lines with open-circles (10% interval) show a binary mixing between magmatic fluid and seawater. Lim/Lic refers Li concentration ratios in magmatic fluid and seawater. Modeling calculation sees Appendix II.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561896&req=5

f3: Oxygen-lithium isotopic compositions of the ore-forming fluids at Gacun, which can be reproduced by mixing of variable amounts of seawater (δ18O = +0‰; δ7Li = +31.5‰) with a magmatic fluid (δ18O = +8‰; δ7Li = +1.5‰) with variable Limagmatic/Liseawater mass mixing ratios.Dot-lines with open-circles (10% interval) show a binary mixing between magmatic fluid and seawater. Lim/Lic refers Li concentration ratios in magmatic fluid and seawater. Modeling calculation sees Appendix II.
Mentions: To date, a few experiments have been performed to determine the Li isotopic fractionation between magmatic fluids and melts3031. A theoretic model shows that the δ7Li of both residual melts and exsolving fluids do not change significantly with progressive fluid exsolution17. Based on Li isotopic compositions of the Gacun rhyolites (δ7Li: +1.0‰ to +2.3‰), we estimate that the δ7Li values of initial fluid exsolving from a rhyolitic melt vary from +1.0‰ to +3.0, close to the lowest measured δ7Li values for the LSO. This means that variation in δ7Lifluid (- 0.7 to +18.5‰) observed at Gacun may be caused by other processes, such as interacting with marine sediments (δ7Li = −1.0 ∼ +24‰)3233 and mixing with seawater (δ7Li = +31.5‰)2426. However, the lack of hydrothermal alteration in the hanging-wall (Triassic shales) and the absence of marine sediments in the host package at Gacun (Fig. 1) rule out the first possibility. All δ7Lifluid data may be interpreted by a binary mixing between magmatic fluid and seawater, which is supported by Li–O isotopic system at Gacun (Fig. 3).

Bottom Line: The δ(7)Li results vary from +4.5‰ to +13.8‰ for fluid inclusions and from +6.7‰ to +21.0‰ for the hosted gangue quartz(9 gangue quartz samples containing primary fluid inclusions).This δ(7)Li range, together with Li-O modeling , suggest that magmatic fluid played a significant role in the ore formation.This study demonstrates that Li isotope can be effectively used to trace magmatic fluids in a seafloor hydrothermal system and has the potential to monitor fluid mixing and ore-forming process.

View Article: PubMed Central - PubMed

Affiliation: Institute of Mineral Resources, CAGS, Beijing 100037, P. R. China.

ABSTRACT
Lithium isotopic compositions of fluid inclusions and hosted gangue quartz from a giant volcanogenic massive sulfide deposit in China provide robust evidence for inputting of magmatic fluids into a Triassic submarine hydrothermal system. The δ(7)Li results vary from +4.5‰ to +13.8‰ for fluid inclusions and from +6.7‰ to +21.0‰ for the hosted gangue quartz(9 gangue quartz samples containing primary fluid inclusions). These data confirm the temperature-dependent Li isotopic fractionation between hydrothermal quartz and fluid (i.e., Δδ(7)Liquartz-fluid = -8.9382 × (1000/T) + 22.22(R(2) = 0.98; 175 °C-340 °C)), which suggests that the fluid inclusions are in equilibrium with their hosted quartz, thus allowing to determine the composition of the fluids by using δ(7)Liquartz data. Accordingly, we estimate that the ore-forming fluids have a δ(7)Li range from -0.7‰ to +18.4‰ at temperatures of 175-340 °C. This δ(7)Li range, together with Li-O modeling , suggest that magmatic fluid played a significant role in the ore formation. This study demonstrates that Li isotope can be effectively used to trace magmatic fluids in a seafloor hydrothermal system and has the potential to monitor fluid mixing and ore-forming process.

No MeSH data available.