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Multi-aliquot method for determining (U plus Th)/He ages of hydrothermal hematite: Returning to Elba TEXT SIZE: A A A
We have used a multi-aliquot method to obtain precise (U + Th)/He ages of hydrothermal hematite and to assess the extent to which He loss from fine-grained hematite caused by diffusion and recoil. Hematite (n = 6) from the Rio Marina mine, Elba (Italy) yields (U + Th)/He ages that range from 5.36 +/- 0.33 to 5.64 +/- 0.11 Ma, giving a weighted mean age of 5.53 +/- 0.14 Ma and an isochron age of 5.25 +/- 0.20 Ma. Ar-40/ Ar-39 data from cogenetic adularia yield flat age spectra with analytically indistinguishable plateau ages (5.575 +/- 0.008 and 5.583 +/- 0.013 Ma). An additional adularia has a more complex spectrum and yields an interpreted age of 5.64 +/- 0.03 Ma. The hematite (U + Th)/He ages overlap the Ar-40/ Ar-39 ages, albeit they are less precise (2-6% vs. 0.2-0.5%). This indicates that the loss of in situ radiogenic He-4 from complex fine-grained hematite, either by diffusion and recoil, is insignificant. The study shows that multi-aliquot method has the potential to reliably deliver precise and accurate ages for iron oxide mineralisation that has not suffered significant post-crystallisation thermal perturbation.
 

Publication name

 CHEMICAL GEOLOGY, 504 151-157; 10.1016/j.chemgeo.2018.11.005 JAN 20 2019

Author(s)

 Wu, Li-Yan; Stuart, Finlay M.; Di Nicola, Luigia; Heizler, Matthew; Benvenuti, Marco; Hu, Rui-Zhong

Corresponding author(s) 

 WU Liyan 
 wuly1982@163.com  
 Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550002, Guizhou, Peoples R China.

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