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R. G. Schmidt

Publications and source records attributed to R. G. Schmidt.

15 recordsLinked to original sources
USGS2006

Distribution of hydrothermally altered rocks in the Reko Diq, Pakistan mineralized area based on spectral analysis of ASTER data

The Reko Diq, Pakistan mineralized study area, approximately 10??km in diameter, is underlain by a central zone of hydrothermally altered rocks associated with Cu-Au mineralization. The surrounding country rocks are a variable mixture of unaltered volcanic rocks, fluvial deposits, and eolian quartz sand. Analysis of 15-band Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the study area, aided by laboratory spectral reflectance and spectral emittance measurements of field samples, shows that phyllically altered rocks are laterally extensive, and contain localized areas of argillically altered rocks. In the visible through shortwave-infrared (VNIR + SWIR) phyllically altered rocks are characterized by Al-OH absorption in ASTER band 6 because of molecular vibrations in muscovite, whereas argillically altered rocks have an absorption feature in band 5 resulting from alunite. Propylitically altered rocks form a peripheral zone and are present in scattered exposures within the main altered area. Chlorite and muscovite cause distinctive absorption features at 2.33 and 2.20????m, respectively, although less intense 2.33????m absorption is also present in image spectra of country rocks. Important complementary lithologic information was derived by analysis of the spectral emittance data in the 5 thermal-infrared (TIR) bands. Silicified rocks were not distinguished in the 9 VNIR + SWIR bands because of the lack of diagnostic spectral absorption features in quartz in this wavelength region. Quartz-bearing surficial deposits, as well as hydrothermally silicified rocks, were mapped in the TIR bands by using a band 13/band 12 ratio image, which is sensitive to the intensity of the quartz reststrahlen feature. Improved distinction between the quartzose surficial deposits and silicified bedrock was achieved by using matched-filter processing with TIR image spectra for reference. ?? 2006 Elsevier Inc. All rights reserved.

Remote Sensing of Environment↗
USGS1990

Faults of the central part of the Lewis and Clark line and fragmentation of the Late Cretaceous foreland basin in west-central Montana

The Lewis and Clark line is a prominent zone of strike-slip, dip-slip, and oblique-slip faults that extends from near Wallace, Idaho, to east of Helena, Montana. Faults of this zone have been intermittently active from Middle Proterozoic to Holocene time, and because of numerous tectonic overprints, controversy continues about displacement directions and times of displacement along specific faults. Geologic mapping shows evidence that many principal faults of the Lewis and Clark line, such as the St. Marys-Helena Valley, Bald Butte, Ninemile, and Osburn faults, had right separation or slip that ranged between 28 and 11 km, and this displacement probably occurred during Late Cretaceous time. Other faults, such as the Elevation Mountain, Placer Creek, and Ranch Creek faults, have Late Cretaceous right separations that range between 8 and 3.2 km, and the Mount Sentinel fault zone has between 6.5 and 3 km of right separation of probable Late Cretaceous age. Subsidiary structures of the Lewis and Clark line postdate Paleozoic and Lower Cretaceous rocks and predate Late Cretaceous stocks at some places; subsidiary faults and folds that have age constraints have slip directions compatible with right slip along adjacent, principal faults. Sedimentation patterns of Lower and Upper Cretaceous rocks indicate that faults of the Lewis and Clark line fragmented the foredeep region of the foreland basin into separate northern and southern basins in Late Cretaceous time. The Lower and Upper Cretaceous Blackleaf Formation (Albian and lower Cenomanian) was deposited in a continuous foredeep basin that extended across the Lewis and Clark line from north of the Canadian border to southwestern Montana, a distance of about 450 km. North of the Lewis and Clark line, middle and upper Cenomanian rocks are absent, and a thin sequence of uppermost Cenomanian to Campanian rocks was deposited in a marine environment that changed to a strand-line and continental environment in early Campanian time. South of the Lewis and Clark line, middle and upper Cenomanian deposits are also absent, but a thick sequence of Turonian-to-Campanian rocks was deposited in brackish water and strand-line environments, and during later Campanian time, in a continental environment. In the region between the St. Marys-Helena Valley and Bald Butte faults, a barrier may have formed that served as a local sediment source between foredeep regions in the northern and southern foreland basin during the period 91 to 75 Ma. South of the Bald Butte fault, an extensional tectonic regime contributed to a higher sediment-accumulation rate in the foredeep region along the north border of the southern basin (30 cm/1,000 yr), as compared to lower sediment-accumulation rates (6.9 and 7.8 cm/ 1,000 yr) in the foredeep region of the south part of the northern basin.

Montana↗
USGS1982

Remote detection of metal anomalies on Pilot Mountain, Randolph County, North Carolina

A biogeophysical technique used successfully to delineate mineralized zones under coniferous forests has been extended to a deciduous region in the Piedmont physiographic province of North Carolina. Pilot Mountain, a hydrothermally altered monadnock within the Carolina slate belt, contains areas of anomalously high amounts of Cu, Mo, and Sn in the soils. Leaves of canopy trees in the mineralized zone also contain significant amounts of Cu. Spectral data acquired from a high-resolution airborne spectroradiometer were processed using a waveform analysis technique to minimize background noise caused by canopy variations and slope effects. Areas containing anomalous metals were detected by spectral changes in the chlorophyll absorption region.

Open-File Report↗
USGS1958

Titaniferous sedimentary rocks in the Cuyuna district, central Minnesot

The ore-yielding main iron-formation of the Cuyuna district is strati-graphically overlain by approximately 300 feet of titaniferous sedimentary rocks, and a field test for titahia has been an effective supplement to customary stratigraphic studies. The titanium is in leucoxene. The sedimentary rocks of the district are highly folded, and the main iron-formation serves as the reference for relative stratigraphic position. The strata older than the main iron-formation are light-gray argillite and siltstone with local lenses of quartzite near the upper contact; the older strata contain about 0.5 percent titania. The main iron-formation is a persistent layer of chemically precipitated ferruginous sediments that contain about 0.2 percent titania. The strata younger than the main iron-formation are gray or black argillite, partly carbonaceous, partly ferruginous, and are transitional into lenses of lean upper iron-formation. At the base of the younger strata, 250-350 feet of argillite and slate contain 1-3.7 percent titania and average 2.0 percent. This titaniferous argillite is similar to argillite higher in the younger sequence which contains less than 1.5 percent titania and averages about 1 percent. There are weathered rocks interpreted as tuffs and basalt flows locally interlayered near the bottom of the titaniferous zone. The basalt contains 1-2 percent titania. The high titania content of the 250-350-foot zone suggests a volcanic origin; the argillite probably is reworked basaltic pyroclastics. A few titaniferous bodies have been found in rocks below, within, and above the main iron-formation and thin titaniferous argillaceous layers occur within the main iron-formation.

Minnesota↗
USGS1957

Bedrock geology at the south-central part of the North Range, Cuyuna district, Minnesota

The Cuyuna iron-ore district is in central Minnesota in Morrison, Crow Wing, and Aitkin Counties. The length of the district is about 68 miles, extending from near Randall in Morrison County ot a point 11 miles east of the community of Hassmann in Aitkin County, and the maximum know width is about 25 miles near the center of the district. Current mining activity is confined to a much smaller area about 10 miles longs and 3 miles wide near Crosby and Ironton in Crow Wing County. This investigation has been restricted to the active area plus a marginal strip in which much exploratory drilling has been done. The average annual production of iron ore and manganiferous iron ore from the district during 1940-50 was slightly more than 3 million tons.

Minnesota↗
USGS1957

Geology of Saipan, Mariana Islands; Part 2, Petrology and soils

The rocks that comprise the volcanic formations of Saipan are of two principal types: dacites, which are characteristically glassy, and andesites, which are comparatively crystalline. The dacites consist primarily of silicic glass, oligoclase, and silica minerals (quartz, tridymite, cristobalite, chalcedony, and opal). Minor constituents in these rocks are green hornblende, biotite, magnetite, and hematite. The andesites are composed principally of labradorite, hypersthene, augite, and subcalcrc augite. Minor but also characteristic constituents of the andesites are quartz, tridymite, cristobalite, anorthoclase, and accessory magnetite, ilmenite, rutile, and apatite. Nine varieties of dacite and andesite are recognized on the basis of chemical composition, mineralogy, and texture. These are dacite, dacite vitrophyre, dacite perlite, hornblende-bearing dacite porphyry, augite-hypersthene andesite, quartz-bearing augite-hypersthene andesite, quartz-bearing augite-hypersthene andesite porphyry, augite andesite, and hypersthene andesite.

Professional Paper↗