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R. J. Horton

Publications and source records attributed to R. J. Horton.

9 recordsLinked to original sources
USGS2011

Geophysical, geochemical, mineralogical, and enivronmental data for rock samples collected in a mineralized volcanic environment, upper Animas River watershed, Colorado

This report provides analyses of 90 rock samples collected in the upper Animas River watershed near Silverton, Colo., from 2001 to 2007. The samples are analyzed for geophysical, geochemical, mineralogical, and environmental rock properties of acid neutralizing capacity and net acid production. The database is derived from both published (n=68) and unpublished (n=32) data. New for all samples are geophysical measurements of electrical resistivity, density, and porosity. Rock samples were acquired from 12 geologic units that include key Tertiary volcanic and plutonic lithologies, all with varying degrees of alteration. The purpose of this study is to * provide a comprehensive and complete record of U.S. Geological Survey rock samples collected and similarly analyzed in the upper Animas River watershed for various physical, chemical, and geoenvironmental properties; * provide measurements of geophysical rock properties of lithologic units to establish ground truth with respect to watershed-scale airborne magnetic and electrical survey data; * use the data to interpret the airborne geophysical anomalies to characterize rocks in terms of acid neutralizing capacity or net acid production; and * provide measurements to study the geochemical, mineralogical, and geophysical characteristics of rocks having weak to extreme degrees of alteration and to develop an understanding of how these characteristics change with alteration type. Data are provided in two digital formats: an Arc/Info geodatabase and a Microsoft Excel spreadsheet.

Data Series↗
USGS1985

Electrical geophysical investigations of massive sulfide deposits and their host rocks, West Shasta copper-zinc district

The West Shasta copper-zinc district, Shasta County, California, contains many volcanogenic sulfide deposits within Middle Devonian rhyolites that have not been highly metamorphosed. The district was selected by the U.S. Geological Survey for intensive geological, geochemical, and geophysical study under the Development of Assessment Techniques (DAT) project because accessible exposures have been created by erosion and mining. This report describes the geophysical methods applied to characterize the electrical properties of selected West Shasta massive sulfide deposits and their host rocks, at both small (less than 25 ft) and large (greater than 25 ft) scales. The electrical techniques used galvanic (spectral induced polarization--SIP) and induction (very low frequency--VLF, slingram, and time domain electro-magnetics--TDEM) methods.In situ spectral induced polarization measurements were carried out to determine whether or not conductive anomalies in the district could be differentiated by their polarization signatures. The sulfide, in situ, induced polarization-phase spectral signatures (the induced polarization effect as a function of frequency) have much less character and lack the distinctive shape reported for other massive sulfide deposits; however, they do have some identifiable massive sulfide traits, such as low resistivity and variable polarizability. The nondescript sulfide spectral signature is attributed to the poor development of polarization processes due to a high percentage of resistive, nonpolarizable gangue minerals, lack of pore space, and limited electrolytic fluids. Large-scale spectral induced polarization measurements over the Hornet orebody have a greater polarization than the in situ measurements. This observation, in addition to the fact that much of the Hornet sulfide body has been removed by previous mining activity, suggests that the dominant polarization processes occur at the ground-water-sulfide interface.Combined use of induction techniques, which have different depths of penetration, were used to locate conductive anomalies and determine their shape and depth. All the induction surveys over the Hornet orebody detected the conductive tabular-shaped massive pyritic sulfide deposit hosted in resistive rhyolite. Shallow penetrating induction methods near the Keystone mine detected a conductive fault zone where a block of shale has been downfaulted into volcanic rock. Integrated interpretation of deeper penetrating induction data over this conductive fault zone indicates that parts of the shale are also conductive, demonstrating that the integrated use of several induction methods provides better conductor definition than a single method.

Economic Geology↗