GEOLOGY AND GEOCHEMISTRY OF THE CHIMNEY CREEK GOLD DEPOSIT, HUMBOLDT COUNTY, NEVADA

Osterberg, Mark Warren

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dc.contributor.advisor	Guilbert, John	en_US
dc.contributor.author	Osterberg, Mark Warren
dc.creator	Osterberg, Mark Warren	en_US
dc.date.accessioned	2011-10-31T18:43:49Z
dc.date.available	2011-10-31T18:43:49Z
dc.date.issued	1990	en_US
dc.identifier.uri	http://hdl.handle.net/10150/187550
dc.description.abstract	Chimney Creek is a sediment-hosted disseminated precious metal deposit located in the Osgood Mountains, Humboldt County, Nevada. It is the first large deposit of this type discovered in rocks affected by the Antler, Sonoma, and Nevadan orogenies and by Tertiary extension. The orebody is in alkalic basalts of the Mississippian Goughs Canyon Formation and the Etchart Limestone, a mixed siliciclastic-carbonate shallow-water sequence of Pennsylvanian- Permian age. These strata are bounded by the Devonian-Mississippian Roberts Mountain Thrust and the Permo-Triassic Golconda Thrust and are dissected by Nevadan and Basin and Range block faulting. The mid-Cretaceous Osgood Mountains Granodiorite intruded these rocks and a complex hydrothermal system evolved in which the Chimney Creek deposit and the other ore deposits of the Osgood Mountains developed. A magmatic-metasomatic auriferous CO₂-H₂O-CH₄ fluid of pH = 4 to 5 flowed upward along fractures in the Goughs Canyon Formation and spread out laterally along permeable beds in the lower member of the Etchart Limestone under a minimum pressure of 800 bars. Pathways in the basalt were armored with wide phyllic selvages and the carbonates were dissolved. Resulting space in the Etchart Limestone was partially filled by stratabound and stratiform silicification when the CO₂-H₂O-CH₄ fluid mixed with a dilute aqueous meteoric fluid and Au was deposited. On average, high enthalpy silica undersaturated solutions removed quartz from the deposit core and low enthalpy silica saturated solutions deposited quartz at the margin, so an outer annulus of bedded jasperoid surrounds a sanded core. This acid-sulfate alteration converted detrital feldspars and illite to phyllosilicates and sulfates in an area at least one kilometer in diameter coincident with conodont CAIs of 4 to 5 and fracture densities greater than 0.2 cm⁻¹. Chimney Creek is a mesothermal fluid mixing acid sulfate sediment-hostel precious metal deposit that formed along with skarn and hot spring type deposits as the Osgood Mountains Granodiorite cooled.
dc.language.iso	en	en_US
dc.publisher	The University of Arizona.	en_US
dc.rights	Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.	en_US
dc.subject	maps
dc.title	GEOLOGY AND GEOCHEMISTRY OF THE CHIMNEY CREEK GOLD DEPOSIT, HUMBOLDT COUNTY, NEVADA	en_US
dc.type	text	en_US
dc.type	Dissertation-Reproduction (electronic)	en_US
dc.type	maps
dc.contributor.chair	Guilbert, John	en_US
thesis.degree.grantor	University of Arizona	en_US
thesis.degree.level	doctoral	en_US
dc.contributor.committeemember	Rider, R. H.	en_US
dc.identifier.proquest	9025074	en_US
thesis.degree.discipline	Geosciences	en_US
thesis.degree.discipline	Graduate College	en_US
thesis.degree.name	Ph.D.	en_US
refterms.dateFOA	2018-09-03T13:13:59Z
html.description.abstract	Chimney Creek is a sediment-hosted disseminated precious metal deposit located in the Osgood Mountains, Humboldt County, Nevada. It is the first large deposit of this type discovered in rocks affected by the Antler, Sonoma, and Nevadan orogenies and by Tertiary extension. The orebody is in alkalic basalts of the Mississippian Goughs Canyon Formation and the Etchart Limestone, a mixed siliciclastic-carbonate shallow-water sequence of Pennsylvanian- Permian age. These strata are bounded by the Devonian-Mississippian Roberts Mountain Thrust and the Permo-Triassic Golconda Thrust and are dissected by Nevadan and Basin and Range block faulting. The mid-Cretaceous Osgood Mountains Granodiorite intruded these rocks and a complex hydrothermal system evolved in which the Chimney Creek deposit and the other ore deposits of the Osgood Mountains developed. A magmatic-metasomatic auriferous CO₂-H₂O-CH₄ fluid of pH = 4 to 5 flowed upward along fractures in the Goughs Canyon Formation and spread out laterally along permeable beds in the lower member of the Etchart Limestone under a minimum pressure of 800 bars. Pathways in the basalt were armored with wide phyllic selvages and the carbonates were dissolved. Resulting space in the Etchart Limestone was partially filled by stratabound and stratiform silicification when the CO₂-H₂O-CH₄ fluid mixed with a dilute aqueous meteoric fluid and Au was deposited. On average, high enthalpy silica undersaturated solutions removed quartz from the deposit core and low enthalpy silica saturated solutions deposited quartz at the margin, so an outer annulus of bedded jasperoid surrounds a sanded core. This acid-sulfate alteration converted detrital feldspars and illite to phyllosilicates and sulfates in an area at least one kilometer in diameter coincident with conodont CAIs of 4 to 5 and fracture densities greater than 0.2 cm⁻¹. Chimney Creek is a mesothermal fluid mixing acid sulfate sediment-hostel precious metal deposit that formed along with skarn and hot spring type deposits as the Osgood Mountains Granodiorite cooled.