Journal article

Assessing the origin of old apparent ages derived by Pb stepwise leaching of vein-hosted epidote from Mount Isa, northwest Queensland, Australia

Robert J Duncan, Roland Maas



Epidote metasomatism affected large areas of tholeiitic metabasalts of the ~1,780 Ma Eastern Creek Volcanics in the Western Fold Belt of the Proterozoic Mount Isa inlier. Hydrothermal epidote generally occurs in quartz veins parallel to or boudinaged within the dominant S2 fabrics which formed during the regional metamorphic peak at ~1,570 Ma associated with the Isan orogeny. Previously published stable isotopic and halogen data suggest that the fluids responsible for epidote formation are metamorphic in origin (with an evaporitic component). Application of the Pb stepwise leaching technique to the epidote does not separate radiogenic Pb4+ and common Pb2+, generating little spread in 206Pb/2..

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Funding Acknowledgements

The Pb step-leaching routine presented here is derived from the unpublished intellectual property of J. Hergt, J. Woodhead, and M. Tonelli (The University of Melbourne). Without their effort, this work would not have been possible. Work here forms part of RJD's PhD within the pmd*CRC (Predictive Minerals Discovery Cooperative Research Centre) with support from Xstrata Copper, and this paper is published with permission. We acknowledge the help of S. McKnight for his help with the epidote imaging. G. Mark, I. Buick, R. Frei, and C. Ballhaus are thanked for providing helpful comments on this manuscript.