TY - JOUR
T1 - A Re-Os study of sulfide minerals from the Bagdad porphyry Cu-Mo deposit, northern Arizona, USA
AU - Barra, Fernando
AU - Ruiz, Joaquin
AU - Mathur, Ryan
AU - Titley, Spencer
N1 - Funding Information:
Acknowledgements We thank Mark Baker and John Chesley for their help in the laboratory, and Robin Bouse who provided some of the samples. Victor Valencia performed microprobe analyses of samples. Analytical work was funded by the National Science Foundation grants EAR 9708361 and EAR 9628150, and instrumentation grant from the W.M. Keck Foundation. The work was also supported by the Wesley Peirce, and the David Lowell scholarships and formed part of the senior author’s M.Sc. research project. We thank Phelps Dodge for allowing us access to the mine and permission to publish this information. Special thanks go to Chris Schmidtz who assisted with sulfide collecting at the Bagdad mine and provided helpful comments. This manuscript has also benefited from constructive reviews by Jason Kirk, John Chesley, Jonathan Patchett, Stephen Rowins, David Selby, and two anonymous reviewers. Editorial comments and suggestions by Richard Goldfarb are greatly appreciated.
PY - 2003/8
Y1 - 2003/8
N2 - Rhenium and osmium isotopes in sulfide minerals from the Bagdad porphyry Cu-Mo deposit have been used to determine timing of mineralization and the source of osmium and, by inference, ore metals. Molybdenite, chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units, which are characterized by moderate to strong potassic alteration (secondary biotite and K-feldspar). Rhenium concentrations in molybdenite are between 330 and 642 ppm. Four Re-Os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71.8 ± 0.2 Ma (2σ). Analyses of a third sample from a molybdenite vein in Precambrian rocks, outside of the main ore zone, yield a weighted average age of 75.9 ± 0.2 Ma (2σ), and provide evidence of two separate mineralization episodes. Chalcopyrite samples contain 6 to 12 ppt Os and 1.7 to 4.1 ppb Re; 187Os/188Os initial ratios are between 0.1 and 0.8. Pyrite samples have osmium and rhenium concentrations varying in the range 8-17 ppt and 3.9-6.8 ppb, respectively. Analyses from these pyrite samples yield an eight-point isochron with an age of 77 ± 15 Ma (2σ) and an initial 187Os/188Os ratio of 2.1 ± 0.8 (MSWD = 0.90). The results presented here add to the growing body of work indicating that porphyry-type mineralization is produced by long-term, multiple episodes of magmatism and associated mineralization. The data also support the hypothesis that a significant part of the metals and magmas may have a crustal source, as has been suggested for other copper deposits and districts in Arizona.
AB - Rhenium and osmium isotopes in sulfide minerals from the Bagdad porphyry Cu-Mo deposit have been used to determine timing of mineralization and the source of osmium and, by inference, ore metals. Molybdenite, chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units, which are characterized by moderate to strong potassic alteration (secondary biotite and K-feldspar). Rhenium concentrations in molybdenite are between 330 and 642 ppm. Four Re-Os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71.8 ± 0.2 Ma (2σ). Analyses of a third sample from a molybdenite vein in Precambrian rocks, outside of the main ore zone, yield a weighted average age of 75.9 ± 0.2 Ma (2σ), and provide evidence of two separate mineralization episodes. Chalcopyrite samples contain 6 to 12 ppt Os and 1.7 to 4.1 ppb Re; 187Os/188Os initial ratios are between 0.1 and 0.8. Pyrite samples have osmium and rhenium concentrations varying in the range 8-17 ppt and 3.9-6.8 ppb, respectively. Analyses from these pyrite samples yield an eight-point isochron with an age of 77 ± 15 Ma (2σ) and an initial 187Os/188Os ratio of 2.1 ± 0.8 (MSWD = 0.90). The results presented here add to the growing body of work indicating that porphyry-type mineralization is produced by long-term, multiple episodes of magmatism and associated mineralization. The data also support the hypothesis that a significant part of the metals and magmas may have a crustal source, as has been suggested for other copper deposits and districts in Arizona.
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U2 - 10.1007/s00126-002-0341-0
DO - 10.1007/s00126-002-0341-0
M3 - Article
AN - SCOPUS:0141501070
SN - 0026-4598
VL - 38
SP - 585
EP - 596
JO - Mineralium Deposita
JF - Mineralium Deposita
IS - 5
ER -