Canyon Member Research Articles

Structurally Controlled Sediment Distribution Patterns and Their Relationship to Uranium Deposits in Jurassic Morrison Formation, Northwestern New Mexico: ABSTRACT

Structures that were active in the Jurassic, inferred from isopleth and structure contour maps, significantly affected depositional patterns in the Westwater Canyon Member of the Morrison Formation in the southern End_Page 852------------------------------ San Juan basin, northwestern New Mexico. Isopleth maps illustrate geometry of the major depositional units, distribution of sandstone depo-centers, and large-scale lithofacies variations within the units. A reconstruction of topography at the base of the Westwater Canyon Member shows a series of subparallel paleotopographic lows and highs that trend east-southeast. The Westwater Canyon is thick and sandy along paleotopographic lows, but is thin and less sandy over the paleogeographic highs. These relationships suggest active structural control of sedimentary facies along east-southeast-oriented folds or faults by differential subsidence during deposition of the unit. Locally, east-southeast-oriented basement faults that were episodically reactivated since the Precambrian may be detect d by detailed seismic reflection studies. Depositional patterns and lithofacies distribution, in turn, appear to have controlled the location of uranium deposits. Primary and remnant uranium ore in the Westwater Canyon is restricted to east-southeast-trending depocenters defined by anomalously thick and sandy facies with relatively high sandstone:mudstone ratios. Redistributed ore is also localized in anomalously thick zones of the Westwater Canyon with relatively low sandstone:mudstone ratios. End_of_Article - Last_Page 853------------

In-Situ Leaching of Crownpoint, New Mexico, Uranium Ore: Part 6-Section 9 Pilot Test

Summary Mobil has successfully recovered uranium by in-situ leaching from a depth of 2,000 ft [610 m] in the Westwater Canyon member of the Morrison formation near Crownpoint, NM. This was the deepest successful in-situ uranium leach carried out in the U.S. and the first in-situ uranium leach in New Mexico. A period of thorough laboratory testing preceded initiation of the pilot. Careful application of conventional petroleum industry drilling procedures and reservoir techniques facilitated project procedures and reservoir techniques facilitated project development. Compared to deep mining, water usage was minimal. After all regulatory approvals were received, the pilot began in Nov. 1979. By using a hydrogen peroxide/alkaline bicarbonate leachate, an average uranium peroxide/alkaline bicarbonate leachate, an average uranium level of slightly greater than 100 ppm was produced during the 10-month leaching phase. The leachate flow was confined to the selected ore zone within the Westwater Canyon member by careful reservoir management. High levels of molybdenum also were produced during leaching. This complicated the functioning of the ion-exchange and precipitation circuits, but methods to control these problems evolved. The leaching demonstration period was insufficient to extract the uranium fully, and period was insufficient to extract the uranium fully, and leaching was terminated after only a part of the uranium resource was recovered so that restoration could proceed. A restoration phase followed the leach phase. During the first 12 months' restoration, all 27 water-quality parameters (New Mexico state standards) except parameters (New Mexico state standards) except molybdenum were reduced below the required limits. In commercial operation, both uranium and molybdenum would be depleted substantially during the leaching phase and should present little problem during restoration. The relatively low front-end capital requirements of in-situ leaching, with its potentialities for development in a step-wise, modular manner, reduce the risk of its implementation in a changing yellowcake market environment. Introduction Northwest New Mexico, in particular the Grants mineral belt, contains extensive and diversified uranium ore deposits that have been studied intensively and described in detail. For the most part, uranium resources have been recovered by standard strip or shaft mining techniques followed by conventional milling methods, and this also has been true in New Mexico. We have recently completed a successfull uranium in-situ leach pilot operation near Crownpoint, and the design, operation, and results of this pilot are described in this paper. A number of field projects and commercial scale in-situ uranium leaching operations in south Texas have been described; these include Mobil's El Mesquite plant, 20 with design production capacity of 650,000 plant, 20 with design production capacity of 650,000 lbm/yr [294 835 kg/a] of yellowcake. Several uranium leaching projects in Wyoming have been reported . We are not aware of any other current in-situ uranium leaching activities in New Mexico, although there are two partially completed underground mining projects partially completed underground mining projects near Crownpoint. Among the many potential advantages of in-situ leaching compared to conventional mining, the lower overall environmental impact is paramount. There is significantly less total water required than for underground mining, and less regional hydrological disturbance and aquifer drawdown, since groundwater is recirculated through wells as in petroleum waterflooding. No surface ore handling or tailings ponds are required, and even extensive well-field acreage presents a "low profile." There is no significant radiation exposure with in-situ leaching. It provides great flexibility in developing a wider, more diffuse area of ore resource than mining, which focuses on a more confined ore zone. The overall resource target is expanded to include lower-grade ore zones, and fewer restrictions on both horizontal and vertical continuity are imposed. Manpower requirements are less than for mining, and there are significantly lower front-end capital costs. In contrast to mining, in-situ leaching is not nearly as sensitive to the economy of scale in plant size, and incremental modular expansion from relatively small projects is feasible. Many of the techniques of the petroleum projects is feasible. Many of the techniques of the petroleum industry can be transferred readily to in-situ leaching -i.e., drilling, logging, casing, cementing, perforation, and stimulation, as well as reservoir analysis, perforation, and stimulation, as well as reservoir analysis, large-scale fluids handling, and engineering design. The Crownpoint development sites are in McKinley County on the southern edge of the San Juan basin. JPT P. 2243

Stratigraphic relations and source areas of ash‐flow sheets of the Black Mountain and Stonewall Mountain Volcanic Centers, Nevada

Recent work has resulted in major changes in the stratigraphic correlations and source‐area assignments of ash‐flow sheets of the late Miocene Black Mountain and Stonewall Mountain volcanic centers, southern Nevada. Ash‐flow tuffs exposed around Stonewall Mountain have different trace element patterns and thermoremanent magnetization directions than do ash‐flow sheetsof the Thirsty Canyon Tuff, erupted from the Black Mountain center, with which they were previously correlated. Hafnium concentrations are particularly useful in distinguishing the megascopically and petrographically similar tuffs ofthe two centers. The ash‐flow sheet overlyingthe Spearhead Member in the Stonewall Mountainarea, herein named the Civet Cat Canyon Member, can be traced northward continuously from outflow facies south of Stonewall Mountain to near‐vent facies on the southern flank of Stonewall Mountain. This, in conjunction with distribution, thickness, and facies relations show that these units are the outflow sheets of the Stonewall Mountain volcanic center; they are herein assigned to a new formation, the Stonewall Flat Tuff of late Miocene age. Tuffs previously mapped near Black Mountain as the Labyrinth Canyon Member (herein abandoned) are correlated on the basis of trace‐element, paleomagnetic, petrographic, and radiometric age data with the type Spearhead Member at Goldfield. Tuffs previously assigned to the Spearhead Member in the Black Mountain frea are reassigned to the Pahute Mesa Member (new) of the Thirsty Canyon Tuff. The Stonewall Mountain volcanic center is thus slightly younger than the Black Mountain center, and the period of time over which the Black Mountain center was active probably was appreciably shorter than was previously inferred. Recognition of the Stone‐wall Flat Tuff as a separate stratigraphic and genetic entity enables us to explain a number of geological inconsistencies, including the marked asymmetric distribution previously attributed to the Thirsty Canyon Tuff. Moreover, the inferred original volume of the Thirsty Canyon Tuff is significantly reduced, increasing the importance of lava relative to tuff in the eruptive history of the Black Mountain center.

Cyclic Deposition and Sea Level Changes: Record in Twin Creek Limestone (Jurassic), Northern Utah: ABSTRACT

The Twin Creek Limestone in northern Utah was deposited in a shallow sea during the Middle Jurassic. Paleocurrent patterns determined from study of ripple marks and cross-stratification, and the distribution of facies, indicate that the average shoreline orientation was northeast-southwest. Two major transgressive-regressive cycles, which are correlated with sea level curves proposed by P. R. Vail and others for the Jurassic, are delineated. The lower cycle in the Twin Creek Limestone unconformably overlies the Lower Jurassic Nugget Sandstone. The Twin Creek Limestone is represented by deposits of the Gypsum Springs, Sliderock, Rich, and Boundary Ridge Members. Lithofacies in this cycle sequence grade upward from reworked Nugget Sandstone at the base into oosparite, micrite, and silty ripple-marked micrite, to an overlying discontinuous red siltstone unit. The cycle is correlative with the J2.1 global cycle of relative change of sea level. The upper cycle is separated from the lower one by a hiatus of unknown duration. This boundary is recognized on the basis of the thin discontinuous red bed at the top of the Boundary Ridge Member. The cycle consists of the Watton Canyon, Leeds Creek, and Giraffe Creek Members. Lithofacies grade from oosparite at the base up into micrite, silty micrite interbedded with sandy oosparite, and sandstone. The upper boundary is marked by the base of the Middle Jurassic Preuss Sandstone. The cycle is correlative with the J2.2 global cycle. Duration of these global cycles is about 8-10 m.y. Recognition of the cycles leads to improvement in stratigraphic and structural interpretation incorporating the effects of sea level changes. End_of_Article - Last_Page 941------------

Correlation of Twin Creek Limestone with Arapien Shale in Arapien Embayment, Utah--Preliminary Appraisal: ABSTRACT

Striking and important stratigraphic patterns have emerged as a result of recent work during which members of the Twin Creek Limestone were correlated with the Arapien Shale, all of Middle Jurassic age. These correlations, determined first on the basis of electric and lithologic logs, are supported by recent palynologic work. Three distinct dinoflagellate assemblages, assigned to the Bajocian(?), Bathonian, and Callovian stages, form the paleontologic basis for these correlations. The Bajocian(?) assemblage is found in rocks of the Sliderock and Rich Members of the Twin Creek Limestone. The Bathonian assemblage is found in units of the Boundary Ridge and Watton Canyon Members of the Twin Creek, and also in units of the lower Arapien Shale (lower Leeds Creek Member of the Twin Creek of Wyoming). The Callovian assemblage is found in rocks of the upper Arapien (upper Leeds Creek and Giraffe Creek Members of the Twin Creek of Wyoming). Isopach maps, based on these correlations, indicate that most of central Utah was the site of a large marine embayment--the Arapien embayment--that was flanked on the west, south, and east by highlands. The maps also suggest that the ancestral Uinta Mountains, a submerged feature, affected sedimentation as early as Bajocian time, and became a significant barrier from the late Bathonian through Callovian. In central Utah, marine carbonates were deposited in the Arapien embayment during deposition of the Gypsum Spring through Watton Canyon Members of the Twin Creek Limestone. During deposition of the Arapien Shale, a major northward regression occurred; the embayment shrank to form a smaller basin--the Arapien basin--that lay directly south of the ancestral Uinta Mountains. Most of the rapien Shale is shallow-water deposits, that formed in the basin under hypersaline conditions. End_of_Article - Last_Page 950------------

Permo-Triassic of Northwestern Paradox Basin Area, Utah: ABSTRACT

The Moenkopi Formation contains estimates of over 1 billion bbl of oil in the northwestern part of the Paradox basin in Emery, Garfield, and Wayne Counties, Utah. The Moenkopi is comprised of four members. The basal unit, the Black Dragon Member, is the most variable member in thickness as a result of infilling topographic relief of the post-Permian topography. The upper three units--the Sinbad, Torrey, and Moody Canyon Members, in ascending order--are principally marine deposits that thicken to the west. The distribution of the underlying Permian units appears to have controlled, in part, the deposition of the Black Dragon Member, with perhaps the Paradox evaporites of Pennsylvanian age adding to the control of the deposition. The Emery uplift did not influence depositio of the Moenkopi, and had ceased influencing deposition of units by the time the Permian White Rim was deposited. The origin of the oils in the Moenkopi Formation is still open to debate. The writer believes that due to the presence of a high percentage of marine rocks, the tight and discontinuous nature of the reservoir rocks, and the character of the oils from the Moenkopi, the source rocks for the oils in the Moenkopi are contained within the Moenkopi Formation. Generation of hydrocarbons occurred in the areas near the accumulations with limited migration distances being necessary. By combining surface and subsurface data on the underlying Permian units, the Moenkopi Formation, and the overlying Upper Triassic Chinle Formation, a more complete stratigraphic and depositional framework for the Moenkopi Formation is possible. The result is a better understanding of the surface accumulations and a better exploration strategy for subsurface accumulations. End_of_Article - Last_Page 943------------

Depositional Environments, Conodont Biostratigraphy, and Porosity Diagenesis of Montoya Group (Upper Ordovician), Sacramento Mountains, South-Central Mexico: ABSTRACT

Intensely dolomitized and siliceous marine carbonates comprise Upper Ordovician strata in the Sacramento Mountains, New Mexico. Pray subdivided these units into lower Montoya, upper Montoya, and Valmont formations. These strata are more appropriately designated the Montoya Group which includes 3 formations: Second Value, Aleman, and Cutter. The subrounded, medium to coarse-grained sandstone rests disconformably on the Lower Ordovician El Paso Formation. This thin sand (Cable Canyon Member of the Second Value Formation) represents a End_Page 457------------------------------ transgression following Middle Ordovician erosion. The transition into the overlying Upham Member of the Second Value is gradational, but can be locally abrupt. The massive, finely crystalline dolostone was originally coral (tabulate and rugose forms) and crinoidal wackestone-packstone. Fossils are poorly preserved by chalcedony replacement. The transition from the relatively shallow-marine sediments into the deeper water strata of the Aleman Formation occurs over several meters. The very finely crystalline, cherty dolostone hosts rynchonellid and dalmanellid brachiopods and bryozoan colonies. Ribbon cherts developed around clusters of fossils. The Aleman changes sharply into chert-free, thin to medium-bedded Cutter. The argillaceous dolomicrite is nonfossiliferous except for conodont , isolated brachiopods, and a Favosites-type coral horizon. Tidal channels, intraclasts, and cyclic bedding indicate peritidal deposition during Cutter deposition. Erosion preceded Fussleman (Silurian?) deposition. Conodont faunas represent shallower conditions than the Montoya faunas of Sweet, but compare favorably for correlation. Panderodus and Belodina faunas characterize the shallow-marine Second Value Formation; deeper water Plectodina and Phragmodus characterize the Aleman; and very shallow-water Rhipidognathus characterizes the Cutter. Ages for the Second Value, Aleman, and Cutter Formations are late Edenearly Maysville, Maysville-early Richmond, and middle-late Richmond, respectively. Dolomitization interrupted early silica replacement of shells, matrix, and sulfates. Mosaic dolomite and epitaxial rims on dolomite cement virtually destroyed all effective porosity. End_of_Article - Last_Page 458------------

Paleogeographic Setting of Pennsylvanian Tyler Formation and Relation to Underlying Mississippian Rocks in Montana and North Dakota

Pennsylvanian sedimentary rocks in the northern Rocky Mountains and in the northern Great Plains of the United States were deposited primarily on a broad marine shelf between the North American craton and the late Paleozoic continental margin in Idaho and adjacent states. The Lower Pennsylvanian (Morrowan) Tyler Formation comprises detrital sediments and some limestone beds in Montana and North Dakota that were deposited along an eastward-transgressing marine shoreline after regional uplift, warping, and faulting had resulted in an erosional unconformity on top of Mississippian strata. The Lower Pennsylvanian shoreline finally extended onto the cratonic interior in eastern North Dakota. Initial Tyler sediments were deposited as a deltaic and fluviolacustrine complex succeeded by littoral deposits as the Early Pennsylvanian shoreline transgressed eastward across the shelf. Sediments were derived mostly from Mississippian rocks exposed and eroded in south-central Montana and adjacent parts of Wyoming, and from the cratonic hinterland in eastern North Dakota. The Tyler Formation is subdivided into the Stonehouse Canyon Member at the base, the Bear Gulch Member, and the Cameron Creek Member at the top. The Stonehouse Canyon Member consists of dominantly carbonaceous mudstone and lenticular sandstone beds that accumulated on a delta shore and plain as offshore bar, beach, channel, levee, lake and swamp, and related deposits. The Bear Gulch Member, which intertongues with the upper part of the Stonehouse Canyon Member, consists mainly of planar-bedded calcareous mudstone that probably formed in a bay or an estuary adjacent to the delta. The Cameron Creek Member, which overlies the two other members, is dominantly red mudstone and represents oxidized subaerial and shoreface deposits on the upper delta platform, the alluvial plain, and the inte tidal mud flats of the encroaching sea. The Cameron Creek grades upward into marine strata of the Lower and Middle Pennsylvanian Alaska Bench Limestone. Pennsylvanian deltaic deposition ceased in the region as the transgressing sea inundated the terrains that had previously supplied sediments to the Tyler delta.

Alteration of Magnetite and Ilmenite in Upper Jurassic Morrison Formation, San Juan Basin, New Mexico: Relationship to Facies and Primary Uranium Mineralization: ABSTRACT

Petrographic studies of outcrop and drill core samples in the Westwater Canyon Member of the Morrison Formation along the southern and western margins of the San Juan basin reveal a close spatial relationship among altered (iron-leached) detrital magnetite and ilmenite (FeTi oxides), depositional facies in the overlying Brushy Basin Member, and distribution of primary uranium deposits. Iron leaching of FeTi oxides resulted from passage of solutions containing soluble organic material; concentrations of this organic material are the sites of the primary uranium orebodies. Along the southern and western parts of the basin, FeTi oxides typically have been leached in the upper Westwater Member, but are unaltered in the lower Westwater; however, locally, leaching occurred thro ghout the Westwater. This zone of leaching systematically thins northward to zero, where unleached FeTi oxides occur throughout the Westwater. Regional patterns of alteration of FeTi oxides correspond to regional facies distribution in the overlying Brushy Basin Member. Extensive FeTi oxide leaching characterizes the Westwater beneath the smectite-rich mud-flat facies of the Brushy Basin, whereas negligible leaching characterizes the Westwater beneath the zeolite-rich playa facies of the Brushy Basin. This correspondence between facies and alteration patterns suggests that solutions responsible for solubilization of organic material, which in turn leached FeTi oxides in the Westwater, originated from the mud-flat facies of the Brushy Basin. Organic material that precipitated from these solutions concentrated uranium to form primary uranium orebodies; therefore, distribution of the Brushy Basin mud-flat facies may define, and restrict, distribution of primary orebodies in the Westwater. End_of_Article - Last_Page 937------------

The stratigraphy and biofacies trends of the Lower Mesozoic Gabbs and Sunrise formations, west-central Nevada

The boundary between the Gabbs and Sunrise formations of west-central Nevada is redefined and the two units are combined to form the new Volcano Peak Group. The Nun Mine, Mount Hyatt, and Muller Canyon members are named and assigned to the Gabbs Formation, and six new lithostratigraphic units for the Sunrise Formation are the Ferguson Hill, Five Card Draw, New York Canyon, Joker Peak, and Mina Peak members. The boundary for the Triassic and Jurassic systems is placed above the last Choristoceras and below the first certain Psiloceras. The section at Ferguson Hill is proposed as the system boundary stratotype. The transgressive–regressive curve for the formations points to a strong tectonic influence, but the late Norian and late Hettangian regressions and early Sinemurian, early Pliensbachian, and early late Pliensbachian transgressions are consistent with inferred eustatic events. The facies and faunal data are consistent with an early Mesozoic record in the western Cordillera suggesting widespread anoxia. The high within-habitat diversity in Neogene offshore benthic communities compared with those in the Mesozoic may correspond to the breakdown of widespread marine anoxic conditions as polar regions cooled and worldwide climatic zonation intensified.

Structural Control of Sedimentation and Distribution of Uranium Deposits in Westwater Canyon Member of Morrison Formation, Northwestern New Mexico: ABSTRACT

Isopleth mapping of the Westwater Canyon and Brushy Basin Members of the Upper Jurassic Morrison Formation in the southern San Juan basin, New Mexico, constructed from approximately 1,800 geophysical logs and 100 measured sections, show that structural elements controlled depositional patterns in these two members. These compilations, which include isopach, sandstone-mudstone ratio, percent sandstone, net sandstone, and average number of shale interbeds per 100 ft (30.5 m) of section, illustrate the geometry of depositional units, the distribution of sandstone depocenters, and large-scale facies variations within the units. Paleotopographic mapping of the base of the Westwater Canyon compiled during this study shows a series of highs and lows trending east-southeast. The estwater Canyon is thin and sand-poor over the paleotopographic highs and thick and sandy along the paleotopographic lows, suggesting active structural control of facies distribution during deposition of this unit. Sedimentation of the Brushy Basin also was affected by some of the same active structural elements. Basement faults, reactivated through time and defined by detailed reflection seismic studies conducted by other workers, apparently exerted a significant influence on depositional patterns in the Morrison Formation. Depositional patterns appear to control the location of uranium deposits. Primary uranium ore in the Westwater Canyon Member is restricted to sandstone depocenters associated with east-southeast-trending isopach thicks and large sandstone-mudstone ratios. Redistributed ore deposits also are concentrated in the vicinity of isopach thicks but in rocks with relatively low sandstone-mudstone ratios. Their location, however, is much more closely related to the position of a regional oxidation-reduction interface whose three-dimensional configuration was influenced regionally and locally by Laramide structures. Remnant ore deposits are relict primary deposits that lie updip of the redox interface in oxidized ground. Sedimentologic controls are similar to those of primary ore. In general, th se remnant deposits have been preserved from oxidation by a unique stratigraphic or structural setting. End_of_Article - Last_Page 1475------------

Origin of Chert in Permian System in Southwestern Utah and Northwestern Arizona: ABSTRACT

Within the Permian System in southwestern Utah and northwestern Arizona, the Brady Canyon Member of the Toroweap Formation and the Fossil Mountain and Harrisburg Members of the Kaibab Formation contain five different forms of chert. These chert forms provide information about the origin and emplacement of chert in the Permian System. The forms present are: rounded chert nodules, ribbon chert, silicified burrows, disseminated chert, and massive chert that grades into limestone. Sources of chert are attributed to upwelling of deep bottom waters, silica-derived from freshwater mixing with saline water in deltaic complexes, and precipitation of silica through biological processes. Examination of fossiliferous rounded chert nodules, silicified burrows, ribbon chert, disseminat d chert, and stringers of chert, indicate that deposition was the result of secondary solution moving through areas with greater porosity. Disseminated chert, found in the Fossil Mountain Member, was deposited in the areas where the porosity was greatest. Massive chert in the Harrisburg Member formed at the water table where dissolution of the limestone occurred. This chert layer was then exposed to erosion. Chert emplacement occurred following the partial dolomitization of the limestone early in the diagenetic history. Some chert appears to have been deposited as secondary cement in the carbonate rock following cementation and dolomitization. Chert horizons in the upper part of the Kaibab Formation suggest that chert may have developed much later during an erosional cycle. This is suppo ted by colloform structures and gradation from a massive chert down to limestone. End_of_Article - Last_Page 525------------

U-Pb ages of uranium ores in the Churchrock uranium district, New Mexico

Examines samples from the largest US uranium-producing region in order to determine ages of mineralization of different orebodies. Uranium from this area has come mainly from arkosic and subarkosic sandstones of the Upper Jurassic Morrison Formation. Several lines of evidence suggest that ages range from Late Jurassic or Early Cretaceous to at least as young as Tertiary. Geologic observations indicate that the oldest (primary) orebodies are tabular in shape and rich in amorphous organic material, whereas the youngest orebodies tend to be poor in amorphous organic material, display roll-front geometry, and are commonly spatially associated with Laramide or younger faults. Both types of ore were formed by relatively lowtemperature, dilute fluids that were essentially ground water in nature. Concludes that the 0- to 1-m.y. U-Pb apparent ages of the United Nuclear Corporation Church Rock Mine relate to redistribution, by roll-front processes, of earlier-formed ores by oxidizing Pleistocene ground waters, perhaps those that resulted in the present-day limonitic zone of the Westwater Canyon Member. Suggests that the 10-m.y. apparent age of sample KM-17-1 may represent an earlier phase of redistributed ore formation, perhaps related to the Tertiary oxidation front that resulted in the present-day hematitic zone of the Westwater Canyon Member.

Determining the Type of Fluid Contained in the Fractures of the Twin Creek Limestone By Using the Dual Laterolog (TM) Tool

Summary This paper describes an experimental log evaluation technique to identify and to evaluate the fractured intervals occurring within the Twin Creek limestone of the Overthrust belt. The area of study is the Yellow Creek field located approximately 3 miles southwest of Evanston, WY. The technique uses the response characteristics of the two resistivity curves from the Dual Later log (TM) (DLL) service to locate the fractured intervals and to identify the fluid type within the fractures. Example logs and cross plots are shown. Introduction Several log measurements and techniques are being used to locate natural fracture systems occurring in various producing reservoir's. This paper describes an empirical technique using the DLL service to identify fractured intervals and to predict the production type. In a reservoir with very low porosity, the resistivity from an electrical device such as a laterolog tool can be affected greatly by a fracture system filled with conductive fluids. A device with a shallow depth of investigation is more affected than one that reads more deeply. This paper develops a theory for this phenomenon and describes application and interpretation of the DLL technique in the Yellow Creek field. Reservoir Characteristics The Twin Creek limestone in the Overthrust belt was deposited during Jurassic time and lies above the Nugget sandstone and below the Preuss sandstone (Fig. 1). It is composed of seven members, each with various degrees of shaliness. The uppermost is the Giraffe Creek member, lithologically characterized as silty to finely sandy, thin-bedded limestone. Below this lies the Leads Creek member, consisting of a soft, shaly limestone that grades into the cleaner, denser Watton Canyon member. The basal bed of the Watton Canyon is a massive, dense, brittle, thin-bedded limestone with 0 to 3% primary porosity. Where the Watton Canyon member outcrops, it weathers into a noticeable rectangular fracture pattern. Tectonic forces acting on this member probably have produced similar fracture patterns. The Watton Canyon grades into the shaly siltstone of the Boundary Ridge member. Directly below this is the Rich member, characterized as a shaly, splintery limestone that becomes softer and shalier at the base, where it forms a sharp boundary with the hard, thin-bedded oolitic limestone of the Slide rock member. Below the Slide rock lies the Gypsum Springs member, consisting of anhydrite and brecciated limestone beds that overlie the Nugget sandstone. The Watton Canyon member is the most prolific producer in the Twin Creek limestone, although hydrocarbons also have been produced from the Leads Creek, Rich, Slide rock, and Gypsum Springs members. Production from the limestone consists of gas with various amounts of condensate and oil. Initial production rates from the Watton Canyon member have been as high as 12 MMcf/D with condensate. An independent study of cores from the Watton Canyon member has found that the total porosity averages I %, with fractures and matrix each contributing 0.5%. Reservoir behavior indicates that the matrix porosity is water saturated, with only the fracture system contributing to the storage and production of hydrocarbons. Log Response Porosities from the sonic and neutron-density cross plot range between 0 and 3 % in the Watton Canyon member. Both track core porosities closely. There is no real indication of secondary porosity from the log measurements at these low porosities. JPT P. 2673^

In-Situ Leaching of Crownpoint, New Mexico, Uranium Ore: Part 1 Mineralogical Frame of Reference

Vogt, T.C.,** SPE, Mobil Research and Development Corp. Dixon, S.A.; Mobil Research and Development Corp. Strom, E.T.; Mobil Research and Development Corp. Johnson, W.F.; SPE, Mobil Research and Development Corp. Venuto, P.B.; SPE, Mobil Research and Development Corp. Summary Before assessing potential for in-situ leaching, it is advantageous to identify the nature of probable reactants in the ore horizon, including both the uranium species and those in the gangue material. We report mineralogical data on an areally broad suite of samples from the Westwater Canyon member of the Jurassic Morrison formation in the Crownpoint area of the Grants mineral belt. Optical microscope, electron microprobe, X-ray diffraction, and spectroscopic and wet chemical analyses were conducted. In these samples, the uranium occurs predominantly as either coffinite or uraninite. The host predominantly as either coffinite or uraninite. The host rock is arkosic sandstone comprising mainly detrital quartz and feldspar. Kaolinite and chlorite are present in claystone clasts, and calcite occurs as a cement. Major trace elements include molybdenum, vanadium, iron, selenium and sulfur. There is carbonaceous organic material in the ore, and it is intimately associated with the uranium mineral when it is coffinite. Geochemical, pyrolytic and 13C nuclear magnetic resonance (NMR) pyrolytic and 13C nuclear magnetic resonance (NMR) analyses indicate that the organic material is probably a very mature, coaly kerogen derived from plant components. Introduction An understanding of reactions involved in leaching chemistry is a key aspect of successful in-situ uranium leaching. Mineralogic characterization of samples from the ore deposit provides identification of reactive uranium and gangue minerals and shows the association and distribution of labile and relatively inert and nonreactive species. Certain criteria have been established to judge the suitability of an ore deposit for uranium recovery by in-situ leaching. The ore deposit must be beneath the water table and must be restricted by impermeable strata above and below the permeable ore zone. The uranium minerals must be contacted easily by leachate injected into the deposit. Subsurface conditions should allow oxidation of the uranium and formation of a soluble complex, by the oxygenated leachate containing a complexing agent, so that the uranium solution can be pumped to the surface for recovery. pumped to the surface for recovery. We are among the first to test in-situ leaching in New Mexico and have pioneered leaching at depths of 2,000 ft (609.6 m); underground or strip mining are the conventional techniques in use in New Mexico.Our Crownpoint project areas are in McKinley County, NM, and are part of the Grants mineral belt (Fig. 1). The origin and the nature of these uranium deposits have been subjects of continuing research. The leases lie to the west and east of the town of Crownpoint. These leases are on the southern edge of the San Juan basin, about 40 miles (64 km) northeast of Gallup and about as far to the northwest of Grants. The surface of the properties is essentially flat, with an elevation of about 6,800 ft properties is essentially flat, with an elevation of about 6,800 ft (2073 m). The major uranium deposits in this area occur in the Westwater Canyon member of the Jurassic Morrison formation (Fig. 2). The subsurface ore depth is about 2,000 ft (609.6 m) in the project areas where the Westwater member is about 260 ft (79.2 m) thick and consists of interbedded sandstone and claystone. The sandstones are crossbedded and contain pebbles and silicified log fragments. The Westwater member is the major water-bearing member of the Morrison formation. The uranium mineralization typically is confined by impermeable claystone strata.The sandstone of the Westwater Canyon member can be classified compositionally as arkose. Detrital components of the sandstone are quartz, feldspar, rock fragments, and carbonaceous debris. JPT P. 2200

The Notch Peak Contact Metamorphic Aureole, Utah: Paleomagnetism of the metasedimentary rocks and the quartz monzonite stock

The Notch Peak pluton, a Late Jurassic granitic stock, intrudes early Paleozoic miogeoclinal strata in the House Range, western Utah. As part of a detailed study to determine textural and chemical changes related to the intrusion, a paleomagnetic reconnaissance has been made of the pluton and its contact aureole. Steep, scattered magnetizations with both polarities present are found in the pluton upon alternating field (af) demagnetization, and they may reflect an original thermoremanence in magnetite that was acquired over at least one polarity reversal. Limestones and argillites in the Big Horse Canyon Member of the Orr Formation (Late Cambrian) were sampled at four stratigraphically controlled sites ranging from unaltered country rock to marble. The site farthest from the pluton is well behaved upon progressive thermal demagnetization and yields a low‐inclination, reversed Paleozoic direction by 400°C. The sites nearer the stock generally have a diffusely defined, two‐polarity, high‐inclination magnetization that reflects remagnetization by the pluton. This magnetization is removed above 300°C, and af demagnetization suggests that it resides in fine‐grained hematite. Of these sites, one appeared nearly unaltered in thin section, whereas the others range from hornfels to skarn. The remagnetization resulted from a late oxidation event related to the intrusion, perhaps from mobilization of groundwater; thus, the country rock has been remagnetized chemically rather than thermally. These results suggest that paleomagnetism may be a useful tool for detecting altered zones around plutons. In addition, no consistent, high‐blocking‐temperature magnetization was found in the aureole rocks; the magnetization of the hornfels was easily measurable at higher steps, but directions changed erratically, and this behavior in part results from the presence of pyrrhotite.

Permian Evaporites, Western Colorado Plateau, Southwestern Utah and Northwestern Arizona: ABSTRACT

Permian rocks of the western Colorado Plateau contain five evaporite units that are separated by one marine sandstone and four limestones in a cyclic relationship. These evaporites were deposited during regressions in the Permian seas that allowed sabkhas to develop between the shallow-marine shelf of the Cordilleran geocline and the nonmarine sediments that were being deposited along the transcontinental arch during Early Permian time. The lowest Permian unit containing gypsum is the Pakoon Formation which represents the first regressive cycle in the Lower Permian. Above the Pakoon Formation is the Quantoweap Sandstone deposited in a shallow-marine environment. Overlying the Quantoweap Sandstone is gypsum and gypsiferous siltstone of the Seligman Member of the Toroweap F rmation, representing the second regression. During this regression a sabkha developed along what is now the western margin of the Colorado Plateau. A marine transgression followed depositing the limestone of the Brady Canyon Member in shallow-marine conditions. The third and largest marine regression produced the gypsum of the Woods Ranch Member of the Toroweap Formation while an eolian environment was depositing the Coconino Sandstone on the east. The last major transgression partly dissolved the gypsum of the Woods Ranch Member, locally generating the erosional unconformity between the Toroweap and Kaibab Formations. Along the present margin of the Colorado Plateau the regression of the Permian sea, which deposited the limestone of the Fossil Mountain Member, marked the development of the final sabkha represented by the gypsum of the Harrisburg Member in the area north of Grand Canyon. The deposition of gypsum in the Harrisburg Member was interrupted by a minor transgression that destroyed some of the underlying gypsum by dissolution and deposited a marine limestone. Alternating gypsum and limestone units are present between the limestone deposited by the minor marine transgressions and the Permo-Triassic boundary, suggesting that fluctuations between sabkha and tidal flat environments occurred before the final regression of the Permian sea. End_of_Article - Last_Page 613------------

Depositional Facies of Cretaceous Spring Canyon Member, Blackhawk Formation, Book Cliffs, Utah: ABSTRACT

Facies study of the Spring Canyon Member indicates a shoreline characterized by beaches and river mouth bars. We envision the wave-affected river mouth bars building seaward and furnishing sediment to the downdrift, protected beaches. The beach sequences are characterized by a shoreface containing laminated-to-burrowed beds overlain by cross-bedded sands and a foreshore of parallel laminated sand. In contrast, the river mouth bar sands are hummocky bedded. Associated transitional marine facies include channel-fill, splay, levee, swamp, and bays containing coal deposits. Three principal coal seams within this facies are related to the three Spring Canyon beaches. The lower two formed in a delta plane. The upper coal is associated with a marginal marine sheet sand. Low sulfur content, roots, plant remains, and continuity of coal seams suggests in-situ coal deposition in swamps flanking channels. Paleocurrent directions within most channels indicate a landward flow perhaps due to storm surges or flood tidal effects. The transitional facies contains abundant marine indicators including oyster shells, terrido borings, Ophiomorpha, and holes excavated by rays. End_of_Article - Last_Page 584------------

The Late Pleistocene and Holocene Fauna and Flora of Vulture Cave, Grand Canyon, Arizona

The Late Pleistocene and Holocene Fauna and Flora of Vulture Cave, Grand Canyon, Arizona

Tartaric Acid Leaching of Selected Ore Samples, Grants Mineral Belt, New Mexico: ABSTRACT

Composite samples of high-grade ore samples from the Doris and Johnny M mines were leached under controlled laboratory conditions to determine which elements are more mobile in the presence of organic acids. The samples selected consisted of -2-µ composites of kaolinite + mixed layer smectite/illite + U-mineral + accessory organic matter and sulfides; and chlorite + mixed layer smectite/illite + U-minerals + accessory organic matter and sulfides. These samples were leached with 0.01 molar tartaric acids in tightly sealed Erlenmeyer flasks, with constant agitation, for 100 hours and the leachates and insoluble residues were analyzed by neutron activation analysis. Uranium, Th, and the REE (rare earth element) were strongly leached and presumably form chelates with the tartaric acid; Na, K, and Ba were also leached but Rb and Cs were either not leached or else fixed on the outer armor of the insoluble residue. Fe and Hf were also leached but Cr, Co, Sb, and Ta concentrated in the insoluble residues. The distribution patterns for the REE for leached and untreated samples are parallel, but the amount of REE leached is proportional to U leached, thus suggesting that organic transport of the REE with U (and Th?) may account for the high REE contents common in many uranium deposits of the Grants mineral belt. The source for the REE and for at least some of the U may have been the Brushy Basin Member (Morrison Formation) for deposits in the underlying Westwater Canyon Member. End_of_Article - Last_Page 557------------