Skip to Main Content
Skip Nav Destination
GEOREF RECORD

The geophysical response of the Goldrush-Fourmile orebody and implications for camp-scale Carlin-type deposit exploration, Cortez District, Nevada

Lee M. Sampson and Nicholas C. Williams
The geophysical response of the Goldrush-Fourmile orebody and implications for camp-scale Carlin-type deposit exploration, Cortez District, Nevada (in Mining geophysics, Jean Legault (editor) and Brendan Howe (editor))
Leading Edge (Tulsa, OK) (February 2021) 40 (2): 122-128

Abstract

Since discovery of the Goldrush and Fourmile deposits, numerous geophysical surveys have been acquired over the footprint of mineralization and surrounding areas to focus exploration. The Goldrush-Fourmile system extends more than 7 km in strike length and averages approximately 300 m wide. Most of the orebody lies more than 300 m below ground surface and continues to depths of more than 900 m. Direct detection of the ore system using geophysical tools is impeded by several factors. The system is relatively flat lying and sits in the hinge of a doubly plunging anticline. This gives the shallowest zones a very small lateral footprint. The ore consists of thin strata-bound zones of silica-sulfide mineralization with a tight alteration selvage. Structural controls along faults are limited, with only small displacements. Strong petrophysical contrasts exist between unaltered rock units. Finally, the terrain is rugged. Resistivity inversions of airborne electromagnetic data show that mineralization sits within a complex zone of resistivity responses. Close to intrusions, the host stratigraphy is resistive. Away from intrusions, the same stratigraphic units show highly variable but commonly very low resistivities. This suggests the possibility of redistribution of carbon around intrusions during premineralization metasomatism. Within the orebody, sulfide content increases conductivity within individual formations related to the distribution of fine-grained sooty pyrite. The geometry of the Red Hill Anticline is imaged as a positive density contrast in the observed gravity and geologically constrained gravity inversions. The positive density contrast represents the gross geophysical signature of denser carbonates within the Paleozoic stratigraphy. Magnetic surveys are crucial for mapping the distribution of igneous rocks and potentially hornfelsed sedimentary rocks. The challenges associated with exploring for deeply buried Carlin mineralization notwithstanding, the application of innovative geophysical tools tuned to assess specific geologic questions, combined with best-practice geologic and geochemical modeling, is helping drive exploration for additional Carlin-type mineralization across the Cortez District.


ISSN: 1070-485X
EISSN: 1938-3789
Serial Title: Leading Edge (Tulsa, OK)
Serial Volume: 40
Serial Issue: 2
Title: The geophysical response of the Goldrush-Fourmile orebody and implications for camp-scale Carlin-type deposit exploration, Cortez District, Nevada
Title: Mining geophysics
Author(s): Sampson, Lee M.Williams, Nicholas C.
Author(s): Legault, Jeaneditor
Author(s): Howe, Brendaneditor
Affiliation: Barrick Gold Exploration, Elko, NV, United States
Affiliation: Geotech, Aurora, ON, Canada
Pages: 122-128
Published: 202102
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 4
Accession Number: 2021-018562
Categories: Economic geology, geology of ore depositsApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Reprinted from Sampson, L. M., and Williams, N. C., The geophysical response of the Goldrush-Fourmile orebody and implications for camp-scale Carlin-type deposit exploration, Cortez District, Nevada, p. 205-216; in Koutz, F. R., and Pennell, W. M., eds., Vision for discovery; geology and ore deposits of the Great Basin, Geological Society of Nevada symposium proceedings, 2020
Illustration Description: illus. incl. geol. sketch maps
N39°25'00" - N41°04'60", W117°15'00" - W115°40'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 202106
Close Modal

or Create an Account

Close Modal
Close Modal