Zirconium-rich Sodic Pyroxenes in Felsic Volcanics from the Warrumbungle Volcano, Central New South Wales, Australia

M. B. Duggan
Bureau of Mineral Resources, G.P.O. Box 378, Canberra, ACT, 2601, Australia

Abstract: Soda-rich pyroxenes in felsic rocks from the Warrumbungle Volcano, central New South Wales, contain up to 14.5 wt. % ZrO2, which is more than double the previously reported maximum ZrO2 in pyroxene. Zr is believed to enter aegirine as the component Na(Fe2+,Mn,Mg)0.5Zr0.5Si2O6 via the coupled substitution: (Fe2+,Mn,Mg)VI+ZrVI = 2(Fe3+)VI. This component exceeds 50 mol. % in some analyses.

Pronounced pyroxene Zr-enrichment is restricted to rocks in which sodic amphibole is the major ferromagnesian mineral, with pyroxene only a minor late-stage phase. The Zr-rich pyroxenes resulted from a combination of host lava peralkalinity, low oxygen fugacity, rapid disequilibrium crystallization and low mobility of the Zr ion. These factors collectively led to the development of interstitial Zr-enriched microdomains in the felsic hosts during their final stages of crystallization.

Keywords: zirconium • pyroxenes • felsic rocks • Warrumbungle Volcano • New South Wales, Australia

Mineralogical Magazine; September 1988 v. 52; no. 367; p. 491-496; DOI: 10.1180/minmag.1988.052.367.07
© 1988, The Mineralogical Society
Mineralogical Society (www.minersoc.org)