Tantalum and niobium contamination from tungsten carbide ring mills: much ado about nothing

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Modern analytical methods such as ICP-MS permit accurate determination of sub-ppm levels of ultra trace elements，and contamination during crushing samples is therefore a potential problem．Nb and Ta are frequently cited as possible contaminants from tungsten carbide crushing equipment．To test this，we analyzed quartz sands pulps prepared both by agate grinding（60 minutes）and crushing separate splits in a tungsten carbide ring mill for varying times（30，60，90 and 120 seconds）．Solution ICP-MS analyses showed that no significant Nb or Ta contamination was present in the ring mill pulps，compared to that ground in agate．This was also the case for the REE，Rb，Y，Zr，Sb，Hf，Th，and U．Combined with a previous test，the results show that Co and W are the only significant contaminants．Rocks powders prepared using tungsten carbide equipment can therefore be used for any geochemical studies with confidence，even when elemental abundances are ＜1 ppm．The possibility of contamination must assessed by each laboratory，however．