Why are samples of detrital zircons treated differently from those used for precise igneous or metamorphic ages?
For detrital zircons, enough grains need to be analyzed to be statistically confident that all populations present are represented by at least one grain. Depending on the reference, this number varies from 60 to 100 grains. Because some grains will be unsuitable for analysis, more than 100 grains should be available for analysis. In contrast, roughly 8-15 analyses of one age, for an igneous or metamorphic zircon, are adequate to statistically delineate it. When cores or overgrowths are present and are of interest, another one to two sets of 8-15 spots are necessary to define each of those ages. Hence, depending on the complexity of the sample, anywhere from 8 to 40 analyses will be sufficient.
