Advanced Argillic and Sericitic Alteration in the Subvolcanic Environment of the Yerington Porphyry Copper System, Buckskin Range, Nevada
Joanna L. Lipske, John H. Dilles, 2000. "Advanced Argillic and Sericitic Alteration in the Subvolcanic Environment of the Yerington Porphyry Copper System, Buckskin Range, Nevada", Part I. Contrasting Styles of Intrusion-Associated Hydrothermal Systems: Part II. Geology & Gold Deposits of the Getchell Region, John H. Dilles, Mark D. Barton, David A. Johnson, John M. Proffett, Marco T. Einaudi, Elizabeth Jones Crafford
Download citation file:
The Buckskin Range lies approximately 4 km west of the Yerington porphyry copper district and hosts the Artesia Lake and Fulstone Spring volcanic sequences that structurally overlie the Yerington batholith. Hy-drothermal alteration minerals characteristic of advanced argillic, sericitic, and marginal porphyry copper-type alteration assemblages have been detected via infrared spectrometry, X-ray diffraction, petrography, micro-probe analysis, and hand-lens based-field mapping in the central Buckskin Range.
It is postulated that high-level alteration in the Artesia Lake Volcanics may be contemporaneous with the main event of sericitic alteration and pyrite deposition in the deeper porphyry copper environment. The presence of sericitic alteration underlying or overprinting hypogene advanced argillic assemblages may imply that fluids responsible for porphyry copper mineralization have ascended to epithermal depths.
The spatial relationships of hydrothermal alteration in the Buckskin Range suggest an evolution of low-pH, sulfide-bearing fluids to nearly neutral, oxide-rich hydrothermal fluids. Sulfide-rich, feldspar-destructive advanced argillic and sericitic alteration is crosscut and overlain by feldspar-stable, oxide-rich sericite-hematite-chlorite alteration. Sericite-hematite-chlorite alteration is abruptly overlain by potassium-added, feldspar-stable calcite-chlorite-hematite alteration, produced by late sodic-calcic or potassium-enriched fluids possibly derived from sedimentary or evaporitic brines.
Figures & Tables
Part I. Contrasting Styles of Intrusion-Associated Hydrothermal Systems: Part II. Geology & Gold Deposits of the Getchell Region
Intrusion-related hydrothermal systems represent a large variety of geologic environments that in some cases form large metallic mineral deposits. The deposits examined in this trip represent the spectrum from systems dominated by magmatic fluid (Birch Creek, California and Yerington, Nevada) to those systems in which intrusions serve as heat engines to drive convectively circulating brines derived from sedimentary rocks (Hum-boldt, Nevada). In these examples, nonmagmatic fluids are largely excluded from more deeply emplaced intrusions in a compressive environment, and the hydrothermal composition and ores (e.g., granite W-F, Cu porphyry and skarn) are dictated by the composition of the magma and its mechanism of crystallization and aqueous fluid generation. Magmatic fluids are less important in the shallow crustal ore environment, but apparently contribute to acidic alteration zones located vertically above source intrusions. Using Humboldt as an example, we propose that the Fe oxide Cu-Au ores in the shallow environment require an abundant source of sedimentary brines (typical of evaporitic environments), high fracture permeability (promoted by an exten-sional setting) to allow aqueous fluid flow and dike emplacement, and shallowly emplaced intrusions to serve as heat sources.
IGNEOUS-RELATED hydrothermal systems constitute the most varied type of geologic environment, ranging in tectonic setting from spreading centers to collisional belts, in depth from the surface to the deep crust, and in sources of materials from purely magmatic to largely external. They comprise perhaps the single most important ore-forming environment, yet most igneous systems lack economically significant mineralization. This variety is attributable to igneous factors such as volatile content and its evolution from the intrusion, and to external factors that include depth of emplacement, host rocks, tectonic environment, and structural setting, which control permeability and access of external fluids to the crystallized intrusion and its contact aureole.
This field trip examines three large but markedly different intrusion-centered hydrothermal systems in the western Great Basin of California and Nevada (Fig. 1, Table 1). Each example represents a major group of these systems worldwide. The field emphasis will be on examining mass transfer features—such as mechanisms for igneous emplacement, degassing of magmatic-aqueous fluids, and fracturing and ductile deformation—that allow variation from near-lithostatic to hydrostatic conditions, incursion of nonmagmatic fluids into the high-temperature environment, and hydrothermal alteration, vein deposition, and wall-rock replacement via aqueous fluids. The broader questions of metallogenic provinces and processes will be raised as a context for the specific sites examined.
The overall emphasis of this trip will be on documenting and understanding the dynamics of igneous-related hydrothermal systems.