Lead isotopes in continental arc magmas and origin of porphyry Cu deposits in Arizona
Isotopic composition of Pb in feldspars and sulfides associated with the porphyry Cu-Mo deposit at Silver Bell, Arizona support the importance of crustal interaction in the origin of some porphyry copper ore deposits. Detailed sampling of late Cretaceous volcanic (8) and plutonic (10) units show an impressive range of Pb isotope composition from a single volcanic center (206Pb/204Pb=17.96-18.50; 207Pb/204Pb=15.54-15.59; 208Pb/204Pb=38.35-38.41). Ores (10 samples) include galena, chalcopyrite, pyrite, and supergene chalcocite range from: 206Pb/204Pb = 18.42 -18.74; 207Pb/204Pb=15.59-15.60; and 208Pb/204Pb=38.35-38.41. Ores most closely related to the major open-pit copper mines have a restricted range of composition (206Pb/204Pb=18.42-18.47). These ore Pbs are associated with the more radiogenic members of the igneous suite. Close correspondence of Pb in ores with that in related igneous rocks indicates a magmatic derivation of Pb disseminated in stockwork chalcopyrite ore and galena in copper skarn. Plots of 206Pb/204Pb against 207Pb/204Pb show a linear array of data just below crustal Pb evolution curves. This suggests derivation from a common source, and calculated 207Pb/206Pb ages for the line yield mid-Proterozoic ages from 1750-1450 Ma, in good agreement with isotopic ages of known Precambrian basement in the region. Most rocks show no evidence of interaction with LIL-element depleted granulitic lower crust, and have higher 207Pb/204Pb than available data from basalts characterizing the subcontinental mantle beneath southern Arizona.
- Research Organization:
- Univ. of California, Santa Barbara (USA)
- OSTI ID:
- 6200053
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Late Cretaceous caldera volcanism and porphyry copper mineralization at Silver Bell, Pima County, Arizona: geology, petrology, and geochemistry
Related Subjects
ARIZONA
COPPER ORES
CHEMICAL COMPOSITION
ISOTOPE DATING
MINERALIZATION
MINERALOGY
PETROGENESIS
CHALCOPYRITE
CRETACEOUS PERIOD
FELDSPARS
GALENA
GEOCHEMISTRY
ISOTOPE RATIO
LEAD ISOTOPES
MAGMA
MAGMATISM
PYRITE
QUANTITATIVE CHEMICAL ANALYSIS
AGE ESTIMATION
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMISTRY
COPPER COMPOUNDS
COPPER SULFIDES
FEDERAL REGION IX
GEOLOGIC AGES
IRON COMPOUNDS
IRON SULFIDES
ISOTOPES
LEAD COMPOUNDS
LEAD SULFIDES
MESOZOIC ERA
MINERALS
NORTH AMERICA
ORES
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA
580100* - Geology & Hydrology- (-1989)
580400 - Geochemistry- (-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)