text: Well, I'm doing a bit of U-Pb dating on zircons as part of my thesis, and I think the way to tell is to sort your grains carefully when you are preparing them for isotopic analyses into similar populations.  Then when you run the different populations in your TIMS, and if you get one population that is significantly older than the other populations, you can assume that this population of zircons is inherited.\n\nAnother problem you might run into is magmatic overgrowths of inherited zircons, which you MAY be able to see under an ordinary petrographic microscope, but which may need to be recognized using CRL light or by doing in-situe laser ablation isotopic analyses.  Magmatic overgrowths on inherited zircons which are anlyzed using a bulk method like TIMS will of course give you bad data which would not be concordant - so if your data is not concordant, you might also be dealing with magmatic overgrowth and inheritance.\n\nI'm going to have to deal with all this in a month or so too... so good luck!