Field Trip Day Three SEG Getchell Region: Pinson Mine Tour
2000. "Field Trip Day Three SEG Getchell Region: Pinson Mine Tour", 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
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This tour of the Pinson mines presents an overview of the main gold-producing zones mined by the Pinson Mining Company. Currently, the mine is in closure and reclamation is well advanced. As a result, access to the pits is limited. The agenda for this tour includes an overview of the CX pit, as well as a traverse along the south CX pit ramp from the hanging wall to the footwall of the CX zone (Fig. 1). The Pinson site tour concludes with a review of core that is representative of mineralization intersected in the deeper parts of the main mineralized zones.
Mine Stop 1: Check in at the Pinson mine gate.
Mine Stop 2: View southwest along the CX zone to the A zone from overlook at the north end of the CX pit.
Mine Stop 3: Traverse of CX pit south ramp.
Mine Stop 4: Core review at the Pinson exploration core shacks.
After touring Pinson mine, we will head for Iron Point. Return to Golconda and get on Interstate 80 eastbound.
Road Log from Golconda to Iron Point Exit
Portions of this log are edited from Jones, A.E., ed., 2000, GSN Road Log 3, Interstate 80 Eastbound, Golconda (Exit 194) to Battle Mountain (Exit 229).
Mileage numbers reflect Interstate 80 mileposts.
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.