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Evidence of Jurassic tectonism from the Barneys Canyon gold deposit, Oquirrh Mountains, Utah

By
Ricardo Presnell
Ricardo Presnell
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William T. Parry
William T. Parry
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Published:
January 01, 1995

Integrated geological and geochemical studies of the Barneys Canyon gold deposit in the Oquirrh Mountains of north-central Utah suggest that compressional tectonism and metamorphism are Jurassic in age. Detailed geologic mapping, clay mineralogy, and fluid-inclusion analyses together with Jurassic K/Ar age determinations indicate that deformation at Barneys Canyon was contemporaneous with regional Jurassic metamorphism recognized in the southern Oquirrh Mountains by Wilson and Parry (1990b).

The Barneys Canyon gold deposit occurs on the crestal region of the Copperton anticline which is interpreted as a fault-bend fold. Bedding-plane gouges formed within the Barneys Canyon sedimentary sequence during flexural slip folding. Clay minerals formed in the gouges and in the Barneys Canyon gold deposit are kaolinite, illite, and some minor interstratified illite-smectite. The distribution of illite and kaolinite shows that the orebody is associated with illite alteration surrounded by a halo of more kaolinitic material. Illite crystallinity suggests that a lower-temperature (retrograde) zone is associated with the orebody.

Fluid-inclusion analyses from quartz and barite show a range of homogenization temperatures from 130–400 °C with two weak modes at 225 °C and 345 °C. Kaolinite and quartz are unstable with respect to pyrophyllite at the higher temperatures. No pyrophyllite has been observed at Barneys Canyon restricting the kaolinitic alteration to the lower-temperature range. The formation temperature of illite is not constrained.

The bedding-plane gouges contain illite, kaolinite (minor), quartz, carbonate, and as much as 1.5 ppm Au. The illites yielded K/Ar ages of 147 Ma and 159 Ma consistent with K/Ar ages of heavy metal bearing illite veins in the southern Oquirrh Mountains described by Wilson and Parry (1990b). This interpretation extends Jurassic deformation to north-central Utah from areas to the west where Jurassic magmatism and tectonics have previously been described.

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GSA Special Papers

Jurassic Magmatism and Tectonics of the North American Cordillera

David M. Miller
David M. Miller
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Cathy Busby
Cathy Busby
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Geological Society of America
Volume
299
ISBN print:
9780813722993
Publication date:
January 01, 1995

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