What does it mean when theres an unknown source assignment?
An unknown source assignment can be attributable to three likely causes: (1) The source is simply not contained in our source reference database, (2) The trace element composition of the analyzed sample fell well outside of the range of variability of our source reference samples, or (3) There was an analytical problem of some kind. To deal with the first two issues, we maintain a very active source research program and we generally analyze a minimum of 15 source samples (when available). When sources with considerable variability are encountered, we continue to analyze samples until we are satisfied that we understand the expected range of trace element values. Analytical problems may be instrumental (spectrometer malfunction) or may be related to a specific sample problem (uneven surface geometry, surface residue, presence of phenocrysts in glass, small sample size). When we suspect that there may be an analytical problem of some sort, we often reanalyze suspect samples to try and is
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