A Re-Os study of sulfide minerals from the Bagdad porphyry Cu-Mo deposit, northern Arizona, USA

Fernando Barra, Joaquin Ruiz, Ryan Mathur, Spencer Titley

Research output: Contribution to journalArticle

93 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)585-596
Number of pages12
JournalMineralium Deposita
Volume38
Issue number5
DOIs
StatePublished - Aug 2003

Fingerprint

Sulfide minerals
Quartz
monzonite
molybdenite
Rhenium
Osmium
porphyry
rhenium
sulfides
Deposits
deposits
minerals
sulfide
mineralization
quartz
osmium
pyrites
pyrite
mineral
chalcopyrite

Keywords

  • Arizona
  • Bagdad deposit
  • Porphyry Cu-Mo
  • Re-Os isotopes

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

A Re-Os study of sulfide minerals from the Bagdad porphyry Cu-Mo deposit, northern Arizona, USA. / Barra, Fernando; Ruiz, Joaquin; Mathur, Ryan; Titley, Spencer.

In: Mineralium Deposita, Vol. 38, No. 5, 08.2003, p. 585-596.

Research output: Contribution to journalArticle

Barra, Fernando ; Ruiz, Joaquin ; Mathur, Ryan ; Titley, Spencer. / A Re-Os study of sulfide minerals from the Bagdad porphyry Cu-Mo deposit, northern Arizona, USA. In: Mineralium Deposita. 2003 ; Vol. 38, No. 5. pp. 585-596.
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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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