Various methods have been devised to determine this initial or common Pb, but all involve making unprovable assumptions.Zircon does incorporate initial Pb when it crystallizes. It cannot be proven that the Pb in apparently cogenetic U- or Th-free minerals is only initial Pb, and that it is identical to the initial Pb in the mineral being dated.Nor can the measured Pb isotope ratios be used to somehow decide what proportions of them are the initial Pb without recourse to unprovable assumptions about the mineral or rock’s history or their interpreted U-Th-Pb ages within an assumed deep time history.
Currently, zircons are typically dated by uranium-lead (U-Pb), fission-track, cathodoluminescence, and U Th/He techniques.
For instance, imaging the cathodoluminescence emission from fast electrons can be used as a prescreening tool for high-resolution secondary-ion-mass spectrometry (SIMS) to image the zonation pattern and identify regions of interest for isotope analysis.
This is done using an integrated cathodoluminescence and scanning electron microscope.
Zircons in sedimentary rock can identify the sediment source.
Zircon is a common accessory to trace mineral constituent of most granite and felsic igneous rocks.
Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircon forms in silicate melts with large proportions of high field strength incompatible elements.For example, hafnium is almost always present in quantities ranging from 1 to 4%.U-Pb radioisotope dating is now the absolute dating method of first choice among geochronologists, especially using the mineral zircon.A variety of analytical instruments have also now been developed using different micro-sampling techniques coupled with mass spectrometers, thus enabling wide usage of U-Pb radioisotope dating.Australia leads the world in zircon mining, producing 37% of the world total and accounting for 40% of world EDR (economic demonstrated resources) for the mineral.