Helium diffusion dating
An empirical case study confirms this variability: two fluorite samples from the same deposit (Horni Krupka, Czech Republic) with could have quantitatively retained helium since the formation of the fluorite-bearing ores in the Permian, despite subsequent Mesozoic burial and associated regional hydrothermal heating.
In contrast, the fluorite with the low yields a Late Cretaceous age close to the apatite fission track (AFT) and apatite (U–Th)/He ages (AHe) from the same locality.
Note carefully: Gentry’s large retentions are not what uniformitarians mean by “excess helium” (Baxter, 2003), a common mental pigeonhole into which they shove helium anomalies.These crystals, called zircons, were radioactive, containing high amounts of uranium and thorium relative to the rest of the rock, as is usual for that mineral.Comparing two isotopes of radiogenic (formed by nuclear decay) lead (U), they determined that 1,500 ± 20 million years worth of nuclear decay had occurred in the zirconsassuming as usual that nuclear decay rates have always been constant (Zartman, 1979).In the context of these zircons, “excess” helium would correspond to retentions greater than 100% of the amount nuclear decay could produce in 1.5 Gyr. As we explain in “Latest results arrive in mid-2003” on page 8 of this paper, the uniformitarian method of “helium dating,” called (U-Th)/He chronometry, is entirely different from the helium diffusion dating we are employing here.Uniformitarian “helium dating” methods would not call attention to the large helium retentions we are concerned with, so it may be that sites like borehole GT-2 are common throughout the world.