February Geosphere media highlights

A new way of doing geology is being invented that is sometimes called "cyber geology." This paper is a pioneering example of this new approach to geologic mapping. Laser scanners and GPS are used to produce high-resolution (approaching one sample per square centimeter) maps of the outcrop of the Jackfork sandstone in the Big Rock Quarry near Little Rock, Arkansas. A three-dimensional virtual model of the outcrop is produced on a computer from this very large (millions of samples) data set. A processing scheme has been implemented that automatically identifies distinct surfaces and their orientations from the three-dimensional point cloud of sample points. These surfaces can be interpreted in terms of fractures and bedding planes in the Jackfork sandstone. The large number of virtual strikes and dip measurements permit a statistical characterization of the fracture orientations as well as an analysis of the special variability of the fractures in different locations within the quarry.

A prominent geophysical feature along the northern Nevada rift and its geologic implications, north-central Nevada
David A. Ponce and J.M.G. Glen, MS989, U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025, USA.
Keywords: gravity and magnetic anomalies, northern Nevada rift, epithermal gold deposits, Battle Mountain-Eureka mineral trend, Basin and Range, Nevada.

The origin and character of a prominent large-scale geophysical feature in north-central Nevada is considered. This crustal-scale fault is coincident with the western margin of the northern Nevada rift—a mid-Miocene rift that includes mafic dike swarms and associated volcanic rocks and is partly coincident with the central part of the Battle Mountain-Eureka mineral trend. Geophysical evidence suggests that the northern Nevada rift partly followed this pre-existing feature in north-central Nevada. If the crustal fault along the northern Nevada rift and a previously inferred crustal fault along the central part of the Battle Mountain-Eureka mineral trend are in fact the same feature, deposits at a greater distance from the crustal feature associated with the northern Nevada rift at Battle Mountain could be explained by post-emplacement tectonic events. In any case, these large-scale crustal features are important to understanding the metallogeny, tectonics, magmatism, and water resources of the Great Basin.

Identification of quartz and carbonate minerals across northern Nevada using ASTER thermal infrared emissivity data—Implications for geologic mapping and mineral resource investigations in well-studied and frontier areas
Barnaby W. Rockwell and Albert H. Hofstra, U.S. Geological Survey, Box 25046, MS 973, Denver Federal Center, Denver, Colorado 80225, USA.
Keywords: remote sensing, ASTER, Thermal infrared, quartz, carbonate