Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Eocene magma plumbing system beneath Cortez Hills carlin-type gold deposit, Nevada; is there a deep-seated pluton?

Celestine N. Mercer
Eocene magma plumbing system beneath Cortez Hills carlin-type gold deposit, Nevada; is there a deep-seated pluton?
Economic Geology and the Bulletin of the Society of Economic Geologists (December 2020) Pre-Issue Publication

Abstract

The magmatic-hydrothermal conceptual model for Carlin-type gold deposit genesis calls upon deep-seated Eocene plutons as the primary source of gold-bearing fluids. However, geophysical surveys, geologic mapping, drilling, geochronology, isotopic tracers, and fluid inclusion chemistry have returned ambiguous evidence for the existence of such plutons. The high-grade Cortez Hills gold deposit in northern Nevada hosts shallow, Eocene syn- and postmineralization intrusions, offering an ideal site to investigate the existence of a deep-seated pluton beneath the district. Here, major and trace element analyses of quartz-hosted melt inclusions from four Eocene rhyolite dikes cropping out within the Cortez Hills pit and results from independent thermobarometers provide a window into the subsurface Eocene magmatic plumbing system to test the existence of a deep-seated source pluton. Dissolved volatile contents, melt inclusion entrapment pressures, and thermodynamic phase equilibria indicate that dike magmas were sourced from approximately 4- to > or =9-km depth from a polybaric magma reservoir residing as a physically and geochemically interconnected crystal mush with extractable or eruptible magma pockets. Magmas ascended adiabatically (nearly isothermally), exsolving fluids, evolving modestly by fractional crystallization, while trapping quartz-hosted melt inclusions steadily from depth to subvolcanic levels where they were emplaced. These data represent the first unequivocal evidence for a deep-seated magma reservoir from which fluid-saturated magma emanated and released magmatic fluids beneath the Cortez district during gold mineralization. However, further investigation into the specific metallogenic potential and metal budget of parental magmas and the partitioning of gold between silicate melt and aqueous fluids will be necessary to provide evidence that exsolved magmatic fluids may have been gold bearing.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: Pre-Issue Publication
Title: Eocene magma plumbing system beneath Cortez Hills carlin-type gold deposit, Nevada; is there a deep-seated pluton?
Affiliation: U. S. Geological Survey, Denver Federal Center, Denver, CO, United States
Published: 20201228
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 78
Accession Number: 2021-011655
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., 1 plate, sketch map
N40°00'00" - N41°00'00", W117°15'00" - W116°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute.
Update Code: 2021
Program Name: USGSOPNon-USGS publications with USGS authors
Close Modal

or Create an Account

Close Modal
Close Modal