Migration of Radiogenic Helium in the Crystal Structure of Sulfides and Prospects of Their Isotopic Dating

Resumo

The migration of helium from the crystal lattices of sulfides (pyrite, pyrrhotite, chalcopyrite, bornite, and sphalerite) and sulfosalts (tennantite and tetrahedrite) was studied. It was shown that helium occurs in submicrometer inclusions of uranium- and thorium-bearing minerals. The curves of helium thermal desorption from the sulfide and sulfosalts were obtained by the step-heating method and analyzed on the basis of the single-jump migration model. The interpretation of these data led to the conclusion on the possibility of the U–Th–He dating of pyrite. It was shown that the migration parameters of helium in the other sulfides and sulfosalts are not suitable for their potential use as U–Th–He geochronometer. Based on a comparison of data on helium migration in various minerals, it was suggested that high helium retentivity in some sulfides and arsenides (pyrite and sperrylite) is related to the type of their crystal lattice, packing density, and specific electric resistivity.