Deep regional resistivity structure across the Battle Mountain-Eureka and Carlin trends, north-central Nevada

Abstract

Magnetotelluric data collected along four, regional scale, southwest-to-northeast profiles show deep resistivity structures beneath the Battle Mountain-Eureka and Carlin gold trends in north-central Nevada, which appear consistent with tectonic breaks in the crust that possibly served as channels for hydrothermal fluids. It seems likely that gold deposits along these linear trends were, therefore, controlled by deep regional crustal fault systems. Two-dimensional resistivity modeling of the magnetotelluric data generally show resistive (30 to 1,000 ohm-m) crustal blocks broken by narrow, sub-vertical, two-dimensional, conductive (1 to 10 ohm-m) zones that are indicative of large-scale crustal fault zones. These inferred fault zones are regional in scale, trend southeast-to-northwest, and extend to mid-crustal (20 km) depths. The conductors are about 3 to 15 km wide, extend from 1 to 8 km below the surface to about 20 km depth, and show two- dimensional electrical structure with general north to northwesterly strikes. From connecting the locations of the conductors together, a single regional crustal fault zone can be inferred that is about 10 km wide within the upper crust and about 150-km long. It coincides with the Battle Mountain-Eureka mineral trend. The images also show regional changes in the resistive crust from north to south. Most of Reese River Valley and Boulder Valley are underlain by a thick (20 km) southwest-to-northeast section of conductive (1 to 10 ohm-m) rock, suggesting that high-temperature fluids are more pervasive in this area (Battle Mountain Heat-Flow High), which implies that the crust beneath these valleys is more fractured than in the areas surveyed to the south.