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Neil S. Fishman

Publications and source records attributed to Neil S. Fishman.

28 records · Page 2Linked to original sources
USGS1990

Iron sulfide minerals at Cement oil field, Oklahoma: Implications for magnetic detection of oil fields

Aeromagnetic anomalies at Cement oil field (Anadarko basin, Oklahoma) have been attributed to authigenic magnetite. The following characteristics of the magnetite, however, indicate that it is contamination introduced by drilling: (1) occurrence as sharp angular blades and as spheres, commonly with metallographic textures typical of industrial alloys and with associated steel and wustite (FeO); (2) presence only in well cuttings and absence from core and quarry samples; and (3) lack of association with detrital framework grains or with authigenic carbonate and sulfide minerals. Ferrimagnetic pyrrhotite occurs in well cuttings, cores, and quarry samples at Cement and is a possible natural source of the magnetic anomalies. Pyrrhotite, which is intergrown with more abundant FeS 2 minerals, formed as a result of hydrocarbon seepage. Pyrrhotite is confined to beds above oil and gas reservoirs. These beds, which lack detrital organic matter, contain higher mineral sulfide and lower mineral sulfate sulfur (1.7 and 0.1 wt %, respectively) than do correlative beds off the field (0.2 and 1.1 wt %, respectively). In the field, isotopic values of sulfide S show a systematic decrease upward through the Permian section from positive values (maximum, +12 per mil at ∼610-760 m depth) to negative values (-1 to -11 per mil between 32 and 230 m; -26 to -30 per mil at the surface). Geochemical results, together with time-temperature data derived from burial curves, limit the major sources of the sulfide in the Fe-S minerals to two possibilities. Isotopically heavy sulfide was generated either inorganically at temperatures >∼90 °C in beds beneath Permian beds, or by bacterial sulfate reduction at temperatures <∼60 °C in Permian strata. If the latter, microbial sulfate reduction occurred under sulfate-limited conditions. The isotopically light sulfide occurring in minerals near the present surface is attributed to bacterial reduction of sulfate. Sulfate-reducing bacteria derived metabolic energy from leaking hydrocarbons and associated organic compounds.

Oklahoma↗
USGS1989

Source of anomalous magnetization in an area of hydrocarbon potential: Petrologic evidence from the Jurassic Preuss Sandstone, Wyoming-Idaho thrust belt

The Jurassic Preuss Sandstone, which crops out in the central part of the Wyoming-Idaho thrust belt on trend with a hydrocarbon-producing region to the south, has been previously identified as the source of anomalous magnetization in the area. Elsewhere, anomalous magnetization in sedimentary rocks near hydrocarbon accumulations has been attributed to hydrocarbon-engendered magnetic minerals, but magnetization of the Preuss is controlled by detrital magnetite. Evidence of a detrital origin for magnetite includes (1) concentration of magnetite grains along laminations containing other heavy minerals, (2) the presence of exsolved ilmenite, hematite, and spinel in the magnetite grains, and (3) titanium contents typical of igneous-derived magnetite. That detrital magnetite is responsible for the anomalous magnetization in the Preuss is further indicated by the systematic eastward decrease in magnetite abundance corresponding to a similar eastward decrease in magnetic susceptibility and remanent magnetization of the unit. Petrologic and vitrinite reflectance studies indicate a complex low-temperature (<150°C or 302°F) diagenetic history for the Preuss. Nevertheless, preservation of detrital magnetite, the presence of diagenetically early ferric oxide minerals, and the absence of sulfide minerals all indicate that the Preuss has not experienced sulfidic-reducing conditions common in areas of hydrocarbon seepage. The marine carbon isotopic composition of calcite that cements most Preuss sandstones (^dgr13C values ranging from -2.47 to 1.48^pmil is evidence that carbonate diagenesis also was not influenced by hydrocarbons. The results of this multidisciplinary study of the Preuss underscore the importance of similar studies when evaluating the sources of aeromagnetic anomalies in areas of hydrocarbon potential.

Idaho, Utah, Wyoming↗
USGS1989

Sulfide mineralization and magnetization, Cement oil field, Oklahoma

Geochemical, petrographic, and rock-magnetic studies were undertaken to investigate possible sources for reported positive aeromagnetic anomalies over the Cement oil field, Oklahoma. Ferrimagnetic pyrrhotite (monoclinic, Fe 7 S 8 ), intergrown with more-abundant, nonmagnetic pyrite (FeS 2 ), is present in well-cutting, core, and quarry samples at Cement, and it is the only identified source of possible enhanced magnetization in rocks over the field. Magnetite, found only in well cuttings from Cement, is contamination from drilling. Magnetite was considered previously by others to be the source of magnetic anomalies at Cement.

Oklahoma↗
USGS1986

Origin of the Mariano Lake uranium deposit, McKinley County, New Mexico

The Mariano Lake uranium deposit, hosted by the Brushy Basin Member of the Jurassic Morrison Formation, occurs in the Smith Lake district of the Grants uranium region, New Mexico. The orebody, contains abundant amorphous organic material, which suggests that it represents a primary-type deposit; however, the orebody is close to a regional reduction-oxidation interface, which suggests that uranium was secondarily redistributed by oxidative processes. Uranium contents correlate positively with organic carbon contents. Petrographic evidence points to uranium residence in amorphous organic material that was post- depositionally introduced in the diagenetic history of the host sandstone. Uranium mineralization was preceded by precipitation of pyrite (δ 34 S values of — 11.0 to — 38.2 per mil), mixed-layer smectite-illite clays, and quartz and potassium feldspar overgrowths; and also partial dissolution of some detrital feldspars. Alterations associated with uranium mineralization include precipitation of the organic material, microcrys- talline quartz, and pyrite and marcasite (δ 34 S values of -29.4 to -41.6 per mil), and the destruction of detrital Fe-Ti oxide grains. Following mineralization, calcite, dolomite, barite, and kaolinite were precipitated, and some iron disulfides were replaced by ferric oxides. Geochemical data and petrographic observations both indicate that the Mariano Lake orebody is a primary-type deposit. Oxidative processes have not noticeably redistributed uranium in the immediate vicinity of the deposit, nor have they greatly modified geochemical characteristics in the ore. Impedance of ground-water flow by local folds and the lower porosity characteristics of ore zones may have helped to preserve the deposit.

New Mexico↗
USGS1986

Iron-titanium oxide minerals and magnetic susceptibility anomalies in the Mariano Lake-Lake Valley cores-Constraints on conditions of uranium mineralization in the Morrison Formation, San Juan Basin, New Mexico

Petrographic study of the Mariano Lake-Lake Valley cores reveals three distinct zones of postdepositional alteration of detrital Fe-Ti (iron-titanium) oxide minerals in the Westwater Canyon Member of the Upper Jurassic Morrison Formation. In the uranium-bearing and adjacent portions of the Westwater Canyon, these detrital Fe-Ti oxide minerals have been thoroughly altered by leaching of iron. Stratigraphically lower parts of the Westwater Canyon and the underlying Recapture Member are characterized by preservation of Fe-Ti oxide grains, primarily magnetite and ilmenite, and of hematite, and by an absence of uranium concentrations. Partly destroyed Fe-Ti oxide minerals occupy an interval between the zones of destruction and preservation. Alteration patterns of the Fe-Ti oxide minerals are reflected in bore-hole magnetic susceptibility logs. Magnetic susceptibility response in the upper parts of the Westwater Canyon Member is flat and uniformly < 500 /xSI units, but at greater depths it fluctuates sharply, from <1,000 to nearly 8,000 μSI units. The boundary between uniformly low and high magnetic susceptibility response corresponds closely to the interval that divides the zone of completely altered from the zone of preserved detrital Fe-Ti oxide minerals. The alteration pattern suggests that solutions responsible for destruction of the Fe-Ti oxide minerals originated in the overlying Brushy Basin Member of the Morrison Formation. Previous studies indicate that these solutions were rich in soluble organic matter and perhaps in uranium. Uranium precipitation may have been controlled by a vertically fluctuating interface between organic-rich solutions and geochemically different fluids in which the detrital Fe-Ti oxide minerals were preserved.

New Mexico↗
USGS1985

Paleomagnetic and petrologic evidence bearing on the age and origin of uranium deposits in the Permian Cutler Formation, Lisbon Valley, Utah

An approximate age for uranium deposits in red beds of the Permian Cutler Formation, Lisbon Valley salt anticline, Utah, was obtained using paleomagnetic techniques. Progressive thermal demagnetization of samples of mineralized sandstone isolates stable magnetization components having high (≳400 °C) unblocking temperatures that define a tilt-corrected mean direction of D = 358.1°, I = 65.5°, α 95 = 3.3°. This direction is close to expected Late Cretaceous to middle Tertiary mean directions at Lisbon Valley. In contrast, thermal cleaning of samples of unmineralized sandstone isolates tilt-corrected southeasterly, shallow mean directions (D = 140.5°, I = −9.5°, α 95 = 8.6°, and D = 155.9°, I = −4.4°, α 95 = 10.9°, for two localities in the Lisbon Valley area). These results are closely similar to results from the Cutler Formation elsewhere on the Colorado Plateau and from other Lower Permian strata in North America. In unmineralized sandstone, the stable remanent magnetization is carried predominantly by martite of postdepositional or detrital origin, whereas in mineralized sandstone, the stable magnetization is carried largely by authigenic specular hematite as uranium- and vanadium-bearing clusters in interstitial areas, and it thus reflects the time of mineralization. Partial dissolution of martite grains and grain-coating ferric oxide pigment prior to formation of abundant interstitial specular hematite has minimized or eliminated the influence of late Paleozoic magnetic components in mineralized sandstone. These results, combined with information on the structural development of the Lisbon Valley area and on nearby uranium deposits in the Triassic Chinle Formation, suggest that the growth of the Lisbon Valley anticline during Late Cretaceous to early or middle Tertiary time promoted oxidative destruction of Chinle orebodies and led to a redistribution of uranium and iron from the Chinle into the Cutler. Acidic solutions generated during destruction of sulfide minerals in Chinle orebodies may account for the simultaneous transport of significant quantities of iron and uranium and for the partial dissolution of martite in the Cutler host beds. Neutralization of these solutions by reaction with host-rock constituents (especially calcite) caused precipitation of amorphous ferric oxide, which incorporated uranium by adsorption and which aged to form specular hematite.

Utah↗
USGS1983

Geochemical characteristics of the Church Rock 1 and 1 East uranium deposits, Grants uranium region, New Mexico

In the Church Rock 1 and 1 East mines, Grants uranium region (GUR), New Mexico, uranium orebodies occur within three sandstone units in the upper part of the Westwater Canyon Member of the late Jurassic Morrison Formation. Geochemical analyses reveal that organic carbon contents in ore samples from all three sand units are uniformly low (most are less than 0.01 percent). Vanadium (ranging from 0.0002 to 0.19 percent) and sulfur (ranging from <0.01 to 0.74 percent) typically show positive correlations with uranium; however, vanadium contents rarely exceed those of uranium in ore samples. Although no systematic relationship of either selenium or molybdenum to uranium is evident, some ore samples contain anomalously high concentrations of either of these elements. Geochemically, the ore deposits of the Church Rock area contrast greatly with primary (tabular) uranium orebodies in the GUR which contain abundant organic carbon and greater amounts of vanadium and sulfur. These differences and radiometric age determinations strongly suggest that the Church Rock ores formed as a result of the redistribution of uranium from preexisting uranium deposits within the last 1 m.y. However, the Church Rock deposits differ geochemically from redistributed orebodies in the Westwater Canyon Member elsewhere in the GUR. Specifically, redistributed orebodies in the Ambrosia Lake district, which are comparable in contents of uranium and organic carbon with the Church Rock deposits, are characterized by vanadium contents typically higher than those of uranium. Similarly, sulfur contents in the redistributed deposits of the Ambrosia Lake district are greater than those found in the Church Rock ores. In addition, anomalously high concentrations of molybdenum have rarely been found in other redistributed orebodies of the GUR.

Open-File Report↗
USGS1982

Origin of the Mariano Lake uranium deposit, McKinley County, New Mexico

The Mariano Lake uranium deposit, hosted by the Brushy Basin Member of the Jurassic Morrison Formation, occurs in the trough of an east-west trending syncline at the western end of the Smith Lake-Mariano Lake group of uranium deposits near Crownpoint, New Mexico. The orebody, which contains abundant amorphous organic material, is situated on the reduced side of a regional reduction-oxidation (redox) interface. The presence of amorphous organic material suggests the orebody may represent a tabular (primary) deposit, whereas the close proximity of the orebody to the redox interface is suggestive that uranium was secondarily redistributed by oxidative processes from pre-existing tabular orebodies. Uranium contents correlate positively with both organic carbon and vanadium contents. Petrographic evidence and scanning electron microscope-energy dispersive analyses point to uranium residence in the epigentically introduced amorphous organic material, which coats detrital grains and fills voids. Uranium mineralization was preceded by the following diagenetic alterations: precipitation of pyrite (ẟ 34 S values ranging from-11.0 to-38.2 per mil); precipitation of mixed-layer smectite-illite clays; partial dissolution of some of the detrital feldspar population; and precipitation of quartz and adularia overgrowths. Alterations associated with uranium mineralization include emplacement of amorphous organic material (possibly uranium bearing); destruction of detrital iron-titanium oxide grains; coprecipitation of chlorite and microcrystalline quartz, and precipitation of pyrite and marcasite (ẟ 34 S values for these sulfides ranging from -29.4 to -41.6 per mil). After mineralization, calcite, dolomite, barite, and kaolinite precipitated, and authigenic iron disulfides were replaced by ferric oxides and hydroxides. Geochemical data (primarily the positive correlation of uranium content to both organic carbon and vanadium contents) and petrographic observations (epigentically introduced amorphous organic matter and uranium residence in this organic matter) indicate that the Mariano Lake orebody is a tabular-type uranium deposit. Oxidative processes have not noticeably redistributed and reconcentrated primary uranium in the immediate vicinity of the deposit nor have they greatly modified geochemical characteristics in the ore. Preservation of the Mariano Lake deposit may not only be related to its position along the synclinal trough, where oxidative destruction of the orebody has been inhibited by stagnation of oxidizing ground waters by the structure, but also due to the deflection of ground waters (resulting from low orebody porosity) around the orebody.

New Mexico↗