Major Crustal Fault Zone Trends and Their Relation to Mineral Belts in the North-Central Great Basin, Nevada

Abstract

The Great Basin physiographic province covers a large part of the western United States and contains one of the world's leading gold-producing areas, the Carlin Trend. In the Great Basin, many sedimentary-rock-hosted disseminated gold deposits occur along such linear mineral-occurrence trends. The distribution and genesis of these deposits is not fully understood, but most models indicate that regional tectonic structures play an important role in their spatial distribution. Over 100 magnetotelluric (MT) soundings were acquired between 1994 and 2001 by the U.S. Geological Survey to investigate crustal structures that may underlie the linear trends in north-central Nevada. MT sounding data were used to map changes in electrical resistivity as a function of depth that are related to subsurface lithologic and structural variations. Two-dimensional (2-D) resistivity modeling of the MT data reveals primarily northerly and northeasterly trending narrow 2-D conductors (1 to 30 ohm-m) extending to mid-crustal depths (5-20 km) that are interpreted to be major crustal fault zones. There are also a few westerly and northwesterly trending 2-D conductors. However, the great majority of the inferred crustal fault zones mapped using MT are perpendicular or oblique to the generally accepted trends. The correlation of strike of three crustal fault zones with the strike of the Carlin and Getchell trends and the Alligator Ridge district suggests they may have been the root fluid flow pathways that fed faults and fracture networks at shallower levels where gold precipitated in favorable host rocks. The abundant northeasterly crustal structures that do not correlate with the major trends may be structures that are open to fluid flow at the present time.

Tracking the Archean-Proterozoic suture zone in the northeastern Great Basin, Nevada and Utah

“…Our resistivity models do not support intact Archean crust this far west and south, suggesting that the magnetic data may be refl ecting other sources, although isolated blocks of rifted Archean crust may exist this far. Rodriguez et al (2007) A r c h e a n Getchell, and Alligator Ridge mineral belts that may be isolated blocks of rifted Archean or Proterozoic crust. Thus, Phanerozoic mineral deposits along these mineral belts may be produced, at least in part (Emsbo et al, 2006;Hofstra and Wallace, 2006), from recycled Archean gold.…”

“…Evidence supporting these interpretations, such as exposures of Cretaceous quartz monzonite, Tertiary granodiorite, widespread recrystallized carbonates, and broad magnetic highs supporting the presence of large, concealed, plutons near MT stations, was reported in Williams (2001, 2002). Subvertical, 2-D, low-resistivity (1-30 ohm-m) conductors that penetrate to mid-crustal depths (5-15 km) may be explained by major crustal-scale fault or fracture zones, while broad, subvertical, low-resistivity (1-30 ohm-m) conductors that penetrate to lower-crustal depths (20 km) may be explained by major crustal-scale suture zones (Rodriguez et al, 2007). The low resistivities can be caused by material associated with faulting or fracture fi lling, such as mylonitic breccia, brine-fi lled fractures, argillaceous alteration from hydrothermal fl uids, substantial graphitic carbon associated with shearing or fl uiddeposited graphite derived from organic shales in the section (Wannamaker and Doerner, 2002), or possibly some combination of these (Eberhart-Phillips et al, 1995).…”

A prominent geophysical feature along the northern Nevada rift and its geologic implications, north-central Nevada

“…Grauch et al (1995) were the fi rst to suggest that the Battle Mountain-Eureka mineral trend, an alignment of a wide range of gold deposits including sediment-hosted and pluton-related gold deposits (Roberts, 1966), corresponds to a basement gravity gradient and that this boundary could be of Jurassic age or older because of an associated alignment of Jurassic plutons and possible folds. Grauch et al (2003aGrauch et al ( , 2003b presented additional evidence that the Battle Mountain-Eureka mineral trend correlates to a major crustal-scale fault zone primarily based on magnetotelluric and radiogenic isotope data (also see Tosdal et al, 2000;Crafford and Grauch, 2002;Rodriguez et al, 2007). Both the Battle Mountain-Eureka mineral trend and the northern Nevada rift occur in a transition zone between the craton to the east and oceanic crust to the west, where the intervening continental margin is defi ned by the initial 87 Sr/ 86 Sr = 0.7060 isopleth (e.g., Tosdal et al, 2000) (Fig.…”