MAJOR CRUSTAL FAULT ZONES TREND OBLIQUELY TO MINERAL BELTS IN THE GREAT BASIN

The Great Basin covers a large part of the Western United States, and hosts one of the world's leading gold producers, the Carlin Trend. Many sediment-hosted gold deposits in the Great Basin occur along such linear trends. The distribution and genesis of these deposits is not fully understood, but most models indicate that regional subsurface structures play an important role in their spatial distribution. Approximately 200 magnetotelluric (MT) soundings were acquired between 1994 and 2005 by the U.S. Geological Survey to investigate crustal structures that may be related to the genesis of gold deposits in the Great Basin. MT sounding data are used to map changes in electrical resistivity as a function of depth that are related to lithologic and subsurface structural variations. The resistivity of geologic units is largely dependent upon their fluid content, pore-volume porosity, fracture porosity, and conductive mineral content.

Two-dimensional resistivity modeling of MT data in the Great Basin reveals primarily northerly and northeasterly trending conductive (1 to 50 ohm-m) zones varying in width from 1- to 30-km and extending to at least 10-km depth that are interpreted to be major shear zones. There are also some easterly and northwesterly trending conductive zones. However, all of the inferred crustal fault zones mapped using MT are oblique to the generally accepted mineral trends. For example, the MT data suggests that the northwesterly mineral belts of the Carlin and Battle Mountain-Eureka (Cortez) trends have inferred major crustal fault zones that are either northerly or northeasterly, while the north trending Independence mineral belt has crustal fault zones that trend either easterly or northeasterly.