ZIRCON RESEARCH

An interesting project recently initiated with Dr. John Hanchar (George Washington University) involves the analysis of gem quality zircons from a carbonatite intrusion in Australia.  Concentrating on the rare earth elements, there was always a discrepancy between in-situ and bulk analyses.  We carefully crushed, washed, sieved, and handpicked the mineral separates and found there were three different categories: A) Dirty (2 x mag.); B) Clean but with tiny inclusions (4 x mag.); C) Clean (2 x mag.).
Initial dissolution using HNO3:HF of 1:10 in Parr Bombs for 10 days resulted in complete dissolution, but significant positive anomalies at Sm and Eu (D).  However, the clean separate compares well with in-situ analyeses, apart from the Sm and Eu anomalies.  These anomalies resulted from ZrF3 interferences.  Changing the proportion of HNO3:HF to 1:1 reduced, but did not eliminate these anomalies (E). Monitoring all isotopes of Sm and Eu allowed corrections to be applied.  Corrected data compare well with lithium metaborate fusions of the same separates (this does not involve HF, so no ZrF3 interferences are possible) (F).  We will be trying a perchloric evaporation stage at 160 degrees after the HF/HNO3 dissolution to try and remove the fluoride, thus removing the need to make these corrections.

Papers resulting from this research:

Jain J.C., Neal C.R., and Hanchar J.M.  (2001) Identification and removal of fluoride interferences in determination of rare-earth elements in zircon by ICP-MS. Geostandards Newsletter 25, 229-237.





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