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ZIRCONIUM AND HAFNIUM IN MINERALS OF THE COLUMBITE AND WODGINITE GROUPS FROM GRANITIC PEGMATITES

Petr ern^1,, T. Scott Ercit², Sten-Anders Smeds³, Lee A. Groat⁴ and Ron Chapman⁵

¹ Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
² Research Division, Canadian Museum of Nature, Ottawa, Ontario K1P 6P4, Canada
³ Department of Earth Sciences, Uppsala University, SE–752 36 Uppsala, Sweden
⁴ Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
⁵ Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

E-mail address: p_cerny{at}umanitoba.ca

Niobium–tantalum-oxide minerals from five localities with moderately to highly fractionated granitic pegmatites were examined for their Zr and Hf contents. Wodginite was found to contain up to 9.59 ZrO₂ and 1.15 wt.% HfO₂, and columbite-group minerals, up to 1.26 and 0.12 wt.%, respectively. The Zr/Hf value is decidedly high in columbite-group minerals (13 to 6) relative to wodginite (4 to 1). Coexisting wodginite-group and columbite-group minerals behave similarly with respect to the overall behavior of Zr + Hf and with respect to the partitioning of Zr versus Hf. In individual pegmatite bodies, no systematic changes in Zr + Hf or Zr/Hf are discernible among the various zones. However, a positive correlation of Zr + Hf with Sn, Mn and Ta is locally observed, and a negative correlation with Ti. No clear trends are shown by Zr/Hf. The Zr/Hf value in the (Nb,Ta)-oxide minerals generally corresponds to its range in associated zircon–hafnon. Considerable depolymerization of highly fractionated, (F, B, P)- and H₂O-rich pegmatite-forming melts, in part alkaline in boundary layers (particularly significant in final stages of consolidation), is responsible for shifting oxygen coordination of Zr and Hf from [8]- to [6]-fold. Consequently, the abundance of zircon decreases, and the (Nb,Ta)-oxide minerals become geochemically significant carriers of Zr and Hf. This effect apparently operates not only in granitic pegmatites but also in other granite-related environments.

Keywords: zirconium, hafnium, niobium, tantalum, wodginite group, columbite group, granitic pegmatite.

This article has been cited by other articles:

				M. A. Galliski, M. F. Marquez-Zavalia, P. Cerny, V. A. Martinez, and R. Chapman THE Ta-Nb-Sn-Ti OXIDE-MINERAL PARAGENESIS FROM LA VIQUITA, A SPODUMENE-BEARING RARE-ELEMENT GRANITIC PEGMATITE, SAN LUIS, ARGENTINA Can Mineral, April 1, 2008; 46(2): 379 - 393. [Abstract] [Full Text] [PDF]