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Fluid Inclusion Geochemistry of Gold-Bearing Quartz Veins of the Juneau Gold Belt, Southeastern Alaska: Implications for Ore Genesis

By
Richard J. Goldfarb
Richard J. Goldfarb
U.S. Geological Survey, Box 25046, Mail Stop 973, Federal Center, Denver, Colorado 80225
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David L. Leach
David L. Leach
U.S. Geological Survey, Box 25046, Mail Stop 973, Federal Center, Denver, Colorado 80225
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Scott C. Rose
Scott C. Rose
U.S. Geological Survey, Box 25046, Mail Stop 973, Federal Center, Denver, Colorado 80225
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Gary P. Landis
Gary P. Landis
U.S. Geological Survey, Box 25046, Mail Stop 973, Federal Center, Denver, Colorado 80225
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Published:
January 01, 1989

Abstract

Microthermometry, laser Raman spectroscopy, and mass spectrometry were used to study fluid inclusions in gold-bearing quartz veins from the mines of the Juneau gold belt, Unmixing of a CO2-rich parent fluid led to the contemporaneous trapping of H2O-dominant and CO2-dominant inclusions during gold deposition at the Alaska-Juneau, Reagan, and Ibex mines. Ore fluids at all other mines were trapped as homogeneous, H2O-dominant fluids, with less than 10 mole percent CO2. Both N2 and CH4 are present at the percent level within the volatile phases in all deposits; H2S makes up one-third of the volatile phase and 2 mole percent of the total ore fluid at the Sumdum Chief mine. The ore fluids contained less than 5 equiv wt percent NaCl. Gold deposition occurred at temperatures above 250°C and at depths of at least 5 km. The gold-forming fluids are believed to have been derived from devolatilization reactions associated with prograde metamorphism of dominantly pelitic, subducted crust.

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Economic Geology Monograph Series

The Geology of Gold Deposits: The Perspective in 1988

Reid R. Keays
Reid R. Keays
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W. R. H. Ramsay
W. R. H. Ramsay
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David I. Groves
David I. Groves
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Society of Economic Geologists
ISBN electronic:
9781629490014
Publication date:
January 01, 1989

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