The genesis of gold deposits along the Carlin trend is not fully understood. Many of the significant mineral deposits in the Carlin trend were formed during the Tertiary as a result of interrelated high-angle basin-and-range faulting, intrusive igneous activity, and hydrothermal processes (Radtke, 1985). According to Shawe (1991), the linearity of the gold deposits along the Carlin trend and the sub-parallel Battle Mountain-Eureka trend suggests that deep-penetrating regional structures controlled the emplacement of magmas generated in the lower part of the crust or upper mantle, and either provided hydrothermal fluids or caused heating of ground waters that were responsible for transport and deposition of the gold ores. To investigate crustal processes that may have contributed to the genesis of gold deposits along the trend, a regional southwest to northeast profile of magnetotelluric (MT) soundings was acquired in 1996 (line MT-MT′, Fig. 1). Two-dimensional resistivity modeling of the MT profile is being used to place constraints on possible heat or magma sources and possible tectonic controls on the linear distribution of mineral deposits.

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USGS1992

Structure of the Reelfoot rift as interpreted from 2-D magnetotelluric models

The results of magnetotelluric (MT) surveys reveal structures associated with the Reelfoot rift, including an axial high-resistivity structure that may be related to intrusions in the central part of the rift or to a previously unrecognized horst. The axis of this resistivity high generally follows the central part of the Reelfoot rift, but its orientation is offset several degrees from the enigmatic Blytheville arch. The MT structural high follows the main part of a northeast-trending seismicity belt, but in the New Madrid, Missouri area electrical structures are more complicated. In this northern part of the study area, the strike of resistivity structures determined from the MT data indicate a nearly north-south direction, rather than the N45°E direction indicated for most of the data. If the axial high-resistivity structure represents a horst, then it may form an interior divide between thick shale basins. Faults bounding the proposed horst may be a controlling factor for the northeast trending seismic zone.

Arkansas, Kentucky, Missouri, Tennessee↗