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J. C. Cole

Publications and source records attributed to J. C. Cole.

At least 37 records · Page 2Linked to original sources
USGS1997

Major structural controls on the distribution of pre-Tertiary rocks, Nevada Test Site vicinity, southern Nevada

The lateral and vertical distributions of Proterozoic and Paleozoic sedimentary rocks in southern Nevada are the combined products of original stratigraphic relationships and post-depositional faults and folds. This map compilation shows the distribution of these pre-Tertiary rocks in the region including and surrounding the Nevada Test Site. It is based on considerable new evidence from detailed geologic mapping, biostratigraphic control, sedimentological analysis, and a review of regional map relationships. Proterozoic and Paleozoic rocks of the region record paleogeographic transitions between continental shelf depositional environments on the east and deeper-water slopefacies depositional environments on the west. Middle Devonian and Mississippian sequences, in particular, show strong lateral facies variations caused by contemporaneous changes in the western margin of North America during the Antler orogeny. Sections of rock that were originally deposited in widely separated facies localities presently lie in close proximity. These spatial relationships chiefly result from major east- and southeastdirected thrusts that deformed the region in Permian or later time. Somewhat younger contractional structures are identified within two irregular zones that traverse the region. These folds and thrusts typically verge toward the west and northwest and overprint the relatively simple pattern of the older contractional terranes. Local structural complications are significant near these younger structures due to the opposing vergence and due to irregularities in the previously folded and faulted crustal section. Structural and stratigraphic discontinuities are identified on opposing sides of two north-trending fault zones in the central part of the compilation region north of Yucca Flat. The origin and significance of these zones are enigmatic because they are largely covered by Tertiary and younger deposits. These faults most likely result from significant lateral offset, most likely in the sinistral sense. Low-angle normal faults that are at least older than Oligocene, and may pre-date Late Cretaceous time, are also present in the region. These faults are shown to locally displace blocks of pre-Tertiary rock by several kilometers. However, none of these structures can be traced for significant distances beyond its outcrop extent, and the inference is made that they do not exert regional influence on the distribution of pre-Tertiary rocks. The extensional strain accommodated by these low-angle normal faults appears to be local and highly irregular.

Nevada↗
USGS1997

Sub-crop geologic map of pre-Tertiary rocks in the Yucca Flat and northern Frenchman Flat areas, Nevada Test Site, southern Nevada

This map displays interpreted structural and stratigraphic relations among the Paleozoic and older rocks of the Nevada Test Site region beneath the Miocene volcanic rocks and younger alluvium in the Yucca Flat and northern Frenchman Flat basins. These interpretations are based on a comprehensive examination and review of data for more than 77 drillholes that penetrated part of the pre-Tertiary basement beneath these post-middle Miocene structural basins. Biostratigraphic data from conodont fossils were newly obtained for 31 of these holes, and a thorough review of all prior microfossil paleontologic data is incorporated in the analysis. Subsurface relationships are interpreted in light of a revised regional geologic framework synthesized from detailed geologic mapping in the ranges surrounding Yucca Flat, from comprehensive stratigraphic studies in the region, and from additional detailed field studies on and around the Nevada Test Site. All available data indicate the subsurface geology of Yucca Flat is considerably more complicated than previous interpretations have suggested. The western part of the basin, in particular, is underlain by relics of the eastward-vergent Belted Range thrust system that are folded back toward the west and thrust by local, west-vergent contractional structures of the CP thrust system. Field evidence from the ranges surrounding the north end of Yucca Flat indicate that two significant strike-slip faults track southward beneath the post-middle Miocene basin fill, but their subsurface traces cannot be closely defined from the available evidence. In contrast, the eastern part of the Yucca Flat basin is interpreted to be underlain by a fairly simple north-trending, broad syncline in the pre-Tertiary units. Far fewer data are available for the northern Frenchman Flat basin, but regional analysis indicates the pre- Tertiary structure there should also be relatively simple and not affected by thrusting. This new interpretation has implications for ground water flow through pre-Tertiary rocks beneath the Yucca Flat and northern Frenchman Flat areas, and has consequences for ground water modeling and model validation. Our data indicate that the Mississippian Chainman Shale is not a laterally extensive confining unit in the western part of the basin because it is folded back onto itself by the convergent structures of the Belted Range and CP thrust systems. Early and Middle Paleozoic limestone and dolomite are present beneath most of both basins and, regardless of structural complications, are interpreted to form a laterally continuous and extensive carbonate aquifer. Structural culmination that marks the French Peak accommodation zone along the topographic divide between the two basins provides a lateral pathway through highly fractured rock between the volcanic aquifers of Yucca Flat and the regional carbonate aquifer. This pathway may accelerate the migration of ground-water contaminants introduced by underground nuclear testing toward discharge areas beyond the Nevada Test Site boundaries. Predictive three-dimensional models of hydrostratigraphic units and ground-water flow in the pre-Tertiary rocks of subsurface Yucca Flat are likely to be unrealistic due to the extreme structural complexities. The interpretation of hydrologic and geochemical data obtained from monitoring wells will be difficult to extrapolate through the flow system until more is known about the continuity of hydrostratigraphic units.

Nevada↗
USGS1996

Summary of hydrogeologic controls on ground-water flow at the Nevada Test Site, Nye County, Nevada

The underground testing of nuclear devices has generated substantial volumes of radioactive and other chemical contaminants below ground at the Nevada Test Site (NTS). Many of the more radioactive contaminants are highly toxic and are known to persist in the environment for thousands of years. In response to concerns about potential health hazards, the U.S. Department of Energy, under its Environmental Restoration Program, has made NTS the subject of a long-term investigation. Efforts supported through the U.S. Department of Energy program will assess whether byproducts of underground testing pose a potential hazard to the health and safety of the public and, if necessary, will evaluate and implement steps to remediate any of the identified dangers. Test-generated contaminants have been introduced over large areas and at variable depths above and below the water table throughout NTS. Evaluating the risks associated with these byproducts of underground testing presupposes a knowledge of the source, transport, and potential receptors of these contaminants. Ground-water flow is the primary mechanism by which contaminants can be transported significant distances away from the initial point of injection. Flow paths between contaminant sources and potential receptors are separated by remote areas that span tens of miles. The diversity and structural complexity of the rocks along these flow paths complicates the hydrology of the region. Although the hydrology has been studied in some detail, much still remains uncertain about flow rates and directions through the fractured-rock aquifers that transmit water great distances across this arid region. Unique to the hydrology of NTS are the effects of underground testing, which severely alter local rock characteristics and affect hydrologic conditions throughout the region. Any assessment of the risk must rely in part on the current understanding of ground-water flow, and the assessment will be only as good as the understanding itself. This report summarizes what is known and inferred about ground-water flow throughout the NTS region. The report identifies and updates what is known about some of the major controls on ground-water flow, highlights some of the uncertainties in the current understanding, and prioritizes some of the technical needs as related to the Environmental Restoration Program. An apparent deficiency in the current understanding is a lack of knowledge about flow directions and rates away from major areas of testing. Efforts are necessary to delineate areas of downgradient flow and to identify factors that constrain and control flow within these areas. These efforts also should identify the areas most critical to gaining detailed understanding and to establishing long-term monitoring sites necessary for effective remediation.

Nevada↗
USGS1993

Geology and genesis of the Baid Al Jimalah tungsten deposit, Kingdom of Saudi Arabia

The Baid al Jimalah tungsten deposit in Saudi Arabia (lat 25 degrees 09'N, long 42 degrees 41'E) consists predominantly of swarms of steeply dipping, subparallel, tungsten-bearing quartz veins and of less abundant, smaller stockwork veins. It is spatially, temporally, and genetically associated with a 569 Ma, highly differentiated, porphyritic, two-feldspar granite that intrudes Late Proterozoic immature sandstones.Paragenetic data from crosscutting veins demonstrate unambiguously a single cycle of magma intrusion and hydrothermal mineralization. Hypogene mineralization can be divided into three periods: (1) early quartz-molybdenite stockwork veining, (2) wolframite- and scheelite-bearing, greisen-bordered veining, and (3) late, quartz-carbonate-fluorite veining. The first two of these three periods can be further divided into several stages that are transitional to each other. The greisen-bordered veins, in particular, show replacement of earlier mineral assemblages by later ones. Precious and base metal veins at Baid al Jimalah East, approximately 1.5 km east of the Baid al Jimalah tungsten deposit, are genetically related to the tungsten deposit and probably formed contemporaneously with the greisenized tungsten-bearing veins.Fluid inclusion and oxygen isotope data indicate that the Baid al Jimalah deposit formed over a temperature range of 120 degrees to 550 degrees C, from low salinity magmatic and metamorphic fluids, and at a depth of about 4.2 km. Early stockwork veins (period 1) formed at low magmatic temperatures (ca. 550 degrees C) from magma-derived (delta 18 O = 9.6-9.7ppm), low-salinity (1-2 wt % NaCl equiv) fluid. This hydrothermal fluid was generally low density and CO 2 rich. All other veins were formed from regionally derived fluid in equilibrium with metamorphic rocks (delta 18 O = 7.9 + or - 1.0ppm at the site of deposition). This fluid probably scavenged most of the period 2 ore-mineral components from a postulated granite batholith whose existence is indicated by a 6-mGal gravity low centered on the deposit. The greisen-bordered tungsten veins (period 2) formed from fluids in the liquid state at temperatures mostly between 380 degrees and 440 degrees C with salinities between 4.5 and 10.9 wt percent NaCl equiv. Late, barren veins (period 3) formed from liquids with salinities between 0.0 and 3.5 wt percent NaCl equiv at temperatures as low as 120 degrees C. The veins at Baid al Jimalah East formed from liquids with salinities between 0 and 4.2 wt percent NaCl equiv at temperatures mostly between about 340 degrees and 390 degrees C. Important volatile constituents in some hydrothermal fluids were CO 2 and CH 4 , in addition to H 2 O and HF. The delta 18 O data on mineral separates of fresh and altered Bald al Jimalah granite, and whole-rock delta 18 O data on country-rock samples as far as 16 km from the deposit, indicate that the rocks in the Bald al Jimalah area were pervasively infiltrated by a fluid with relatively high delta 18 O values. Interaction and exchange of the country rocks with this delta 18 O fluid led to an increase in the delta 18 O values of volcanic rocks of the Jurdhawiyah Group but to a decrease in the delta 18 O values of the high value delta 18 O Murdama Group sandstones, resulting in a hydrothermal anomaly exceeding 100 km 2 in area. This fluid had an estimated delta 18 O value of about 6 to 8 per mil, essentially identical to that of the metamorphic water calculated from the vein quartz, thus strongly supporting the conclusion that all of the mineral deposits at Baid al Jimalah (except for the early-stage quartz-molybdenite veins), as well as the 12-km 2 geochemical anomaly surrounding the deposit, were from the same metamorphic fluid.Bald al Jimalah is similar in character and origin to Phanerozoic tungsten-tin greisen deposits throughout the world, especially the Hemerdon deposit in Devon, England. It is also analogous to Climax-type molybdenum deposits, which contain virtually identical mineral assemblages, but with the relative proportions of molybdenum and tungsten mineralization reversed, primarily owing to differences in oxygen fugacity. This similarity in mineralization styles and fluid histories indicates that metallogenic processes in granite-related deposits in the late Precambrian were similar to those seen in the Phanerozoic.

Economic Geology↗
USGS1990

Metallic-mineral assessment of the Aban Al Ahmar quadrangle, sheet 25F, Kingdom of Saudi Arabia

Comprehensive detailed interdisciplinary study assesses the metallic-mineral-resource potential in the Aban Al Ahmar Quadrangle of the Kingdom of Saudi Arabia, located in the eastern margin of the northeastern Arabian Shield, utilizing techniques of geophysics, geologic mapping, remote sensing and geochemistry. The landscape of the study area is characterized by isolated mountain groups, inselbergs, and local tracts of dissected hills separated by broad, low-relief peneplain. Topics covered include mining and exploration history; geological setting; interpretation of geophysical anomalies; limonitic hydrothermally altered and mineralized rocks; geochemical interpretation; mineral resource potential; skarn deposiits associated with intermediate igneous rocks; gold deposits; tin/tungsten skarn deposits; etc.

Aban Al Ahmar quadrangle↗
USGS1983

Geologic interpretation of geophysical data for the Wadi al Jarir and Al Jurdhawiyah quadrangles, sheets 25/42 C and D, Kingdom of Saudi Arabia

Interpretations of aeromagnetic and gravity data made in support of geologic mapping clearly outline the near-surface shape of Proterozoic granitic units in the Wadi al Jarir (25/42 C) and Al Jurdhawiyah (25/42 D) 1:100,000-scale quadrangles of the northern part of the Arabian Shield. The aeromagnetic data show marked correlation with the surface geology, and the resulting interpretation defines nine magnetic provinces inferred to reflect bodies of granitic rock possessing homogeneous magnetic properties. Several magnetic lineations of possible structural significance are identified and probably relate to Najd faulting. Older structures of the Hijaz tectonic cycle cannot unequivocally be defined. Four of the younger granitic bodies are interpreted to be tabular in cross-section and of finite thickness on the basis of magnetic anomalies defined by high-amplitude, short-wavelength, positive anomalies along the southern margin of the body and counterpart negative anomalies along the northern margin. One of these bodies, a granodiorite porphyry in the northwestern part of the Al Jurdhawiyah quadrangle, is estimated to be from 4 to 7 km thick on the basis of calculations of gravity data. Older granites possess no edge anomalies and therefore are interpreted to extend to greater depth. Peralkaline granites are distinctively nonmagnetic and are identifiable in the aeromagnetic data as areas of little magnetic relief. Correlation of aeromagnetic data and mineral deposit information provide justification for some prospecting guides. Small granodiorite-porphyry plutons with distinct edge anomalies in Murdama metasediments commonly are associated with copper-gold-bearing quartz veins. Vein orientations in these and most other known deposits in the northeastern Shield cannot be sensibly related to the stress field of the Najd fault system, and are believed to predate the Najd or to have been governed by local factors. Small, weakly magnetic targets such as the Bald al Jimalah West tungsten deposit are not indicated by the regional magnetic data.

Open-File Report↗