Depends on quite a few factors as well. Was the sample crushed...

Depends on quite a few factors as well. Was the sample crushed or was it just a field sample? If it's a field sample, then pretty unreliable. You could just have a good patch which is not indicative of the whole sample. A mine I worked at had very patchy ore and if you knew what you were looking for you could manipulate a high reading or get a very low one from the dirt right beside it. Rely on handheld XRF at your peril.