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Geology; March 2009; v. 37; no. 3; p. 223-226; DOI: 10.1130/G25439A.1
© 2009 Geological Society of America
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Direct dating of Fe oxide-(Cu-Au) mineralization by U/Pb zircon geochronology

Peter M. Valley1,*, John M. Hanchar1 and Martin J. Whitehouse2

1Department of Earth Sciences, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X5, Canada
2Laboratory for Isotope Geology, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden


Figure 01
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  		Figure 1. Simplified geologic map of northeastern Adirondack Mountains with sample locations for this study marked on detailed unit maps: PH—Palmer Hill; AH—Arnold Hill; OB—Old Bed; SM—Skiff Mountain (modified after Isachsen and Fisher, 1970; Whitney and Olmsted, 1993).

 

Figure 02
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  		Figure 2. Representative backscattered electron images of zircon grains. A: Grain typical of ore zircon from Arnold Hill. B: Host granite zircon. Single spot ages are given as 207Pb/206Pb ages corrected for common Pb. Sample names correspond to Table DR1 (see footnote 1).

 

Figure 03
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  		Figure 3. Tera-Wasserburg concordia diagrams (207Pb/206Pb vs. 238U/206Pb) showing zircon ages. A: Palmer Hill granite. B: Palmer Hill ore. C: Arnold Hill granite. D: Arnold Hill ore. E: Skiff Mountain ore. Uncertainties on quoted concordia ages (A–E) (Ludwig, 2003) are 2{sigma}. Filled black error bars on plot—weighted mean averages of common Pb corrected 207Pb/206Pb age for Old Bed Ore (n = 28). Bracketed error bars are 207Pb/206Pb age of samples assumed to be least affected by Pb loss (n = 4) and are used to calculate separate weighted average age for Old Bed Ore (F). Open error bars in F are not used in age calculation. Error ellipses and error bars are 2{sigma} in all samples. MSWD— mean square of weighted deviates.

 




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