Reactivated Palaeozoic normal faults: controls on the formation of Carlin-type gold deposits in north-central Nevada

Abstract

Mappable surface structures control linear trends of Carlin-type gold deposits in north-central Nevada. Some of these structures probably resulted from reactivation of Palaeozoic normal faults, linked to underlying basement faults that originated during rifting of western North America during the Proterozoic. These old faults served as conduits for deep crustal hydrothermal fluids responsible for formation of Carlin-type gold deposits in the Eocene. The reactivated structures are recognized by stratigraphic and structural features. Stratigraphic features include rapid facies changes, growth fault sequences and sedimentary debris-flow breccias. Structural features resulted from inversion of the normal faults during the Late Palaeozoic Antler and subsequent orogenies. Inversion features include asymmetric hanging-wall anticlines, flower-like structures, and 'floating island' geometries. Inversion resulted in structural culminations that occur directly over the basement faults, providing an optimal setting for the formation of Carlin-type gold deposits.

Semiautomatic and Automatic Cooperative Inversion of Seismic and Magnetotelluric Data

“…Drilling in the study area and the previous works (Cline et al 2005;Muntean et al 2011Muntean et al , 2007Thoreson et al 2000) suggest that cover rocks include unconsolidated sediments, valley-filled sediment, alluvium and interbeds of volcanics. The cover sequences are considered to be less prospective for primary gold, while basalt, mudstone, quartzite and tuff are prevalent in the Palaeozoic basement rocks.…”

“…Cover depths range from less than 100 m to more than 500 m, and the base of the cover sequence often has a sharp clear geo-electrical transition to more electrically resistive basement. The transition between cover and basement is an unconformity between Palaeozoic sediments that we define as ''basement'' and the younger ''cover'' sequences (Cline et al 2005;Muntean et al 2011Muntean et al , 2007Thoreson et al 2000).…”

Regional crustal-scale structures as conduits for deep geothermal upflow

“…Coupled with the fact that reactivated structural zones have been shown to control fluid flow associated with ore deposition in the Great Basin and around the world (Breach, 1976;Glen and Ponce, 2002;Grauch et al, 2003;Muntean et al, 2007;Pili et al, 1997;Ponce and Glen, 2002;Rasmussen et al, 2007;Tosdal et al, 2000), this suggests that structural reactivation can be associated with significant permeability enhancement. Permeability enhancement and fluid flow along structures are probably episodic and structures may alternate between open to fluid flow and being effectively sealed to fluid flow in both space and throughout time (Sibson, 1995).…”

Geometry of the Neoproterozoic and Paleozoic rift margin of western Laurentia: Implications for mineral deposit settings

“…The CryogenianDevonian rift-related normal faults in the unexposed basement rocks at depth along different margin segments were inverted during younger (late Paleozoic and Mesozoic) thickskinned contractional deformations forming structural culminations at different scales (cf. Crafford and Grauch, 2002;Muntean et al, 2007;Mair et al, 2006). As a corollary, the relatively narrow rift margins, which formed as upper-plate margins, are more intensely overprinted by magmatic activity; these are the southern Canadian Cordillera segment and the eastern Washington to eastern Idaho segment.…”

“…The host rocks were deposited in subbasins above deep crustal structures that were secondary features of this segment of the Cordilleran rift margin (Tosdal et al, 2000;Crafford and Grauch, 2002). The subbasin-controlling structures formed as rotated crustal blocks during northeast-southwest Neoproterozoic-early Paleozoic extension, were reactivated during renewed Devonian extension events forming pathways for mineralizing basinal brines (Hofstra and Cline, 2000;Cline et al, 2005;Emsbo et al, 2006), and were inverted during contractional deformation in the Mesozoic, further opening pathways for younger mineralizing systems (Emsbo et al, 2006;Muntean et al, 2007). Structures in the mineral belts were reactivated again during initiation of the Yellowstone hotspot (Ponce and Glen, 2002), but the main Miocene rift faults may have been infl uenced by northeast-striking Neoproterozoic and Paleozoic structures.…”