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Porphyritic Intrusions of the Helen Zone in the Cove Deposit, Lander County, Nevada

Zoller, Kevin M
http://rave.ohiolink.edu/etdc/view?acc_num=akron1398079611

Abstract Details

2014, Master of Science, University of Akron, Geology.
The Cove deposit of the northern Fish Creek Mountains of Lander County, Nevada, has been known for its high grade Carlin-style and polymetallic vein type gold deposits. The mineralization of this deposit is directly related to nearby dikes that act as feeders for the mineralizing hydrothermal fluids that entered the system in multiple pulsing events. Northwest of the Cove open pit is the Helen Zone deposit, where mineralization can be found in decarbonized dolostone in the Home Station Member and decalcified limestone in the Favret Member as well as in the limbs of an anticline. Previous studies have not characterized the intrusions of the Helen Zone other than noting barren granodioritic dikes and sills that seem to postdate mineralization. This study of fifty-eight dill core samples from intrusions at the Helen Zone, in conjunction with field and drill core samples from McCoy and Cove, has resulted in the identification of three igneous rocks suites that dominate the area and a total of three different magma series involved in the development of the Cove deposit. The two igneous suites at Helen Zone consist of andesites that are geochemically similar to the Brown Stock of the McCoy pit and a younger, alkalic basalt. Geochemical similarities between the andesites and the Brown Stock suggest that the andesitic rocks were emplaced between ~41-39 Ma during prograde/retrograde pulsing events that occurred throughout the entire McCoy/Cove system. The basaltic dikes are believed to be associated with a different magma series and have been emplaced during a later event. A third igneous rock unit, classified as a dacite, was discovered beneath the Cove open pit and contains higher concentrations of silica and potassium. The dacite unit is characterized by a high degree of sulfidation and presence of pyroclastic material. Geochemical and stratigraphic evidence suggests that the dacites are also associated with a separate magma series and have been emplaced prior to Eocene magmatic activity. Two unique alteration styles can be found in the intrusions of the Helen Zone. The basaltic samples are dominated by a chlorite-sericite alteration and the andesitic samples contain predominantly potassic alterations with an overprinting phyllic alteration and in some samples a later propylitic alteration. Carbonate rich fluids were injected into the systems at different stages in the rocks history and these fluids partially or completely altered phenocrysts and certain matrix minerals. The comparative analysis of data from the Helen Zone to geochemical data of a study by du Bray (2007) of igneous rocks in northern Nevada indicates that samples from the Cove deposit have similar geochemical trends. The similar geochemical trends suggests a similar genetic origin for the intrusions at the Cove deposit to those found elsewhere in northern Nevada.
LaVerne Friberg, Dr. (Advisor)
John Peck, Dr. (Committee Member)
John Szabo, Dr. (Committee Member)
252 p.
Chemistry; Geochemistry; Geological; Geology; Mineralogy; Mining; Petrology
Cove; Nevada; Gold; Intrusions; Helen Zone; dikes; igneous; porphyritic

Recommended Citations

Citations

  • Zoller, K. M. (2014). Porphyritic Intrusions of the Helen Zone in the Cove Deposit, Lander County, Nevada [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1398079611

    APA Style (7th edition)

  • Zoller, Kevin. Porphyritic Intrusions of the Helen Zone in the Cove Deposit, Lander County, Nevada. 2014. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1398079611.

    MLA Style (8th edition)

  • Zoller, Kevin. "Porphyritic Intrusions of the Helen Zone in the Cove Deposit, Lander County, Nevada." Master's thesis, University of Akron, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1398079611

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.