TIN-LEAD ALLOY CONTAMINATION IN POLISHED EPOXY GRAIN MOUNTS OF HEAVY MINERALS

Polished epoxy grain mounts are commonly used for optical analyses of the heavy mineral fraction of unconsolidated sediments. Yet there has been limited discussion of contamination particular to the preparation of epoxy grain mounts. Examination of 116 thin sections under transmi tted and reflected light revealed tin-lead and diamond paste contamina tion in mineral samples from till collected in central New Brunswick. The contamination was found as fracture infillings and as a separate o paque phase with inclusions of other material. Although it has a strik ing resemblance to naturally occurring mineralization, the contaminati on was found to have been introduced during the lapping stage of the p reparation of the grain mounts. Such contamination must be expected an d identified as a preliminary step in heavy mineral analysis. Misident ification of this contamination could result in erroneous conclusions of syngenesis between it and resistant mineral content of the sample. This could be especially problematic in studies of garnet or sulfide m ineralogy.Polished epoxy grain mounts are commonly used for optical an alyses of the heavy mineral fraction of unconsolidated sediments. Yet there has been limited discussion of contamination particular to the p reparation of epoxy grain mounts. Examination of 116 thin sections und er transmitted and reflected light revealed tin-lead and diamond paste contamination in mineral samples from till collected in central New B runswick. The contamination was found as fracture infillings and as a separate opaque phase with inclusions of other material. Although it h as a striking resemblance to naturally occurring mineralization, the c ontamination was found to have been introduced during the lapping stag e of the preparation of the grain mounts. Such contamination must be e xpected and identified as a preliminary step in heavy mineral analysis . Misidentification of this contamination could result in erroneous co nclusions of syngenesis between it and resistant mineral content of th e sample. This could be especially problematic in studies of garnet or sulfide mineralogy.