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Lead isotopes in continental arc magmas and origin of porphyry Cu deposits in Arizona

Conference · · Geol. Soc. Am., Abstr. Programs; (United States)
OSTI ID:6200053
;
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-
Conference Information:
Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
580300 -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
AGE ESTIMATION
ARIZONA
CHALCOGENIDES
CHALCOPYRITE
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
COPPER COMPOUNDS
COPPER ORES
COPPER SULFIDES
CRETACEOUS PERIOD
FEDERAL REGION IX
FELDSPARS
GALENA
GEOCHEMISTRY
GEOLOGIC AGES
IRON COMPOUNDS
IRON SULFIDES
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LEAD COMPOUNDS
LEAD ISOTOPES
LEAD SULFIDES
MAGMA
MAGMATISM
MESOZOIC ERA
MINERALIZATION
MINERALOGY
MINERALS
NORTH AMERICA
ORES
PETROGENESIS
PYRITE
QUANTITATIVE CHEMICAL ANALYSIS
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA