9:30 AM - 9:45 AM
[SCG51-03] Hematite U-Pb geochronology by LA-ICP-MS
Keywords:Hematite, U-Pb dating, LA-ICP-MS, Skarn
Zircon uranium (U)-lead (Pb) dating is a common method to determine the age of formation of rocks. Zircon contains a relatively large amount of U which produce a certain amount of radiogenic Pb through the radioactive decay of U. It leads to high precision analysis of U and Pb.
Furthermore, there is the advantages that zircon itself is a physically and chemically robust mineral, and its isotopic system relatively easily maintains a closed system. On the other hand, U-Pb datings of other minerals which have not traditionally been subject to the dating are also attempt. U-Pb dating of garnet and calcite has already been carried out, and a method for U-Pb dating of hematite has been developed (e.g. Coutney-Davies et al., 2021)
Hematite is an ore mineral that occurs in vairous deposit types, especially iron oxide copper-gold deposits (IOCG type). Therefore, U-Pb dating of hematite is considered to be an effective dating method to directly determine the age of ore formation. In this study, we established a U-Pb dating method for hematite as a method for determining the direct age of ore formation. Hematite (Fe2O3) contains trace amounts of U through the following substitution reaction (Ciobanu et al., 2013);
2Fe3+ ↔ U6+ + vacancy (up to 0.013 atoms per formula unit)
The closure temperature of U-Pb system in hematite is estimated about 400 oC (Coutney-Davies et al., 2021).
In this study, we present hematite U-Pb dating by LA-ICP-MS and its application. As an application, we selected hematites in Waga Sennin Fe-Cu skarn deposits, Iwate Prefecture, Japan. Cretaceous granodiorite intruded in the Permian sedimentary rock in the area, then Miocene rhyolite intruded further. There are two interpretation of skarn formation; contact metamorphism due to Cretaceous granodiorite or Miocene rhyolite. The result of U-Pb dating of hematite show that hematite crystallized in Miocene.
Acknowledgement
We appreciate Dr. L. Courtney-Davies to provide us the MR-HFO. This work is financially supported by the Japan Mining Promotive Foundation.
Reference
Ciobanu et al. (2013) Precambrian Research, 238, 129-147.
Coutney-Davies et al. (2021) Chemical Geology, 513, 54-72.
Furthermore, there is the advantages that zircon itself is a physically and chemically robust mineral, and its isotopic system relatively easily maintains a closed system. On the other hand, U-Pb datings of other minerals which have not traditionally been subject to the dating are also attempt. U-Pb dating of garnet and calcite has already been carried out, and a method for U-Pb dating of hematite has been developed (e.g. Coutney-Davies et al., 2021)
Hematite is an ore mineral that occurs in vairous deposit types, especially iron oxide copper-gold deposits (IOCG type). Therefore, U-Pb dating of hematite is considered to be an effective dating method to directly determine the age of ore formation. In this study, we established a U-Pb dating method for hematite as a method for determining the direct age of ore formation. Hematite (Fe2O3) contains trace amounts of U through the following substitution reaction (Ciobanu et al., 2013);
2Fe3+ ↔ U6+ + vacancy (up to 0.013 atoms per formula unit)
The closure temperature of U-Pb system in hematite is estimated about 400 oC (Coutney-Davies et al., 2021).
In this study, we present hematite U-Pb dating by LA-ICP-MS and its application. As an application, we selected hematites in Waga Sennin Fe-Cu skarn deposits, Iwate Prefecture, Japan. Cretaceous granodiorite intruded in the Permian sedimentary rock in the area, then Miocene rhyolite intruded further. There are two interpretation of skarn formation; contact metamorphism due to Cretaceous granodiorite or Miocene rhyolite. The result of U-Pb dating of hematite show that hematite crystallized in Miocene.
Acknowledgement
We appreciate Dr. L. Courtney-Davies to provide us the MR-HFO. This work is financially supported by the Japan Mining Promotive Foundation.
Reference
Ciobanu et al. (2013) Precambrian Research, 238, 129-147.
Coutney-Davies et al. (2021) Chemical Geology, 513, 54-72.