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Integrative Approaches to Elucidate the Structural Architecture of the Roberts
Mountains Allochthon and Recognize Transverse Deformation Zones Within It That
Conceal and Localize Carlin-Type Gold Deposits in Nevada: Christopher Holm-Denoma


Project Title: Integrative Approaches to Elucidate the Structural Architecture of the Roberts Mountains Allochthon and Recognize Transverse Deformation Zones Within It That Conceal and Localize Carlin-Type Gold Deposits in Nevada
Mendenhall Fellow: Christopher Holm-Denoma, (303) 236-5454, cholm-denoma@usgs.gov
Duty Station: Denver, CO
Start Date: March 17, 2008
Education: Ph.D. (Geological Sciences), Florida State University, 2006
Research Advisors:Albert H. Hofstra, (303) 236-5530, ahofstra@usgs.gov; Byron R. Berger, (303) 236-5533, bberger@usgs.gov; Jonathan S. Caine, (303) 236-1822, jscaine@usgs.gov; Donald S. Sweetkind, (303) 236-1828, dsweetkind@usgs.gov; Alan R. Wallace, (775) 784-5789, alan@usgs.gov
  Christopher Holm-Denoma

Project Description: The Great Basin physiographic province is the nation’s premier gold mining region and is currently the world’s second leading producer of gold. Most of this gold is produced from Carlin-type gold deposits that occur in linear belts/trends (fig 1). As described by Hofstra and Cline (2000), the majority of Carlin-type gold deposits are Eocene disseminated deposits hosted in calcareous Paleozoic sedimentary rocks exposed in erosional windows through antiforms in the Roberts Mountains allochthon (RMA). The trends and antiforms that localize the deposits are transverse to the continental margin and RMA.

Generalized location of the RMA
      relative to Carlin-type deposits   Figure 1. Map displays generalized location of the RMA relative to Carlin-type deposits (open circles). GT-Getchell Trend; CT-Carli Trend; JC-Jerritt Canyon/Independence Range (highlighted in orange); AB-Alligator Ridge/Bald Mountain; C-Central; Dashed lines represent mineral trends (oblique to structural fabric); Red line is approximate Pb and Sr isotope boundary (continental margin?) Modified from Arehart et al. (2003).

Crystalline basement in north central Nevada is only exposed locally, but geochemical and geophysical patterns suggest that the edge of the buried North American basement occurs proximal to many of the mineral districts in central Nevada. The rifted margin of North America is likely to impart a large effect upon the locations of ore-fluid flow as well as inheritance and structural modification to tectonic elements thrust upon or across this margin (Emsbo et al., 2006). The effect of inversion and convergence over a continental margin is well documented in many fold-and-thrust-belts (for example, Tull and Holm, 2005), and often the thrust elements incur transverse modification as well as major along-strike discontinuities along these transverse zones. 

Most of the Carlin-type gold deposits in the windows have been found (fig. 2). Hence, current exploration involves drilling (to depths of 1 to 2 km) through adjacent areas of the RMA. Consequently, the goal of the project is to elucidate the thickness and structural architecture of the RMA and the attributes of transverse deformation zones within it to help target Carlin-type gold deposits as well as assessment of mineral resources.

Geologic map
          of the Jerritt Canyon/Independence Range area  

Figure 2. Geologic map of the Jerritt Canyon/Independence Range area (modified from A.H. Hofstra, written communication; and an unpublished geologic map of Jerritt Canyon by Queenstake Resources, Ltd. The general geology is overlain on the existing map for simplification. Dos-Undifferentiated Snow Canyon, McAffee Quartzite, and Jacks Peak Fms; DSt-Lower plate assemblage. The Mississippian foreland sediments are exposed locally. Units starting with ‘T’ are generally volcanic rocks while ‘Q’ units are modern cover deposits.

References: Emsbo, P., Groves, D.I., Hofstra, A.H., and Bierlein, F.P., 2006, The giant Carlin gold province; A protracted interplay of orogenic, basinal, and hydrothermal processes above a lithospheric boundary: Mineralium Deposita, v. 41, p. 517–525.

Hofstra, A.H., and Cline, J.S., 2000, Characteristics and models for Carlin-type gold deposits: SEG Reviews v. 13, p. 163–220.

Tull, J.F., and Holm, C.S., 2005, Structural evolution of a major Appalachian salient-recess junction: Consequences of oblique collisional convergence across a continental margin transform fault: Geological Society of America Bulletin, v. 117, no. 3/4, p. 482–499.


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