Thermochronology of secondary minerals from the Yucca Mountain unsaturated zone
No abstract available.
Nevada↗
Geology topics
Edwin Roedder
Publications and source records attributed to Edwin Roedder.
Fluid-inclusion data on samples from Creede, Colorado, in relation to mineral paragenesis
Published and unpublished data on 2575 fluid inclusions in ore and gangue minerals from the Creede, Colorado, Ag-Pb-Zn-Cu vein deposit collected in our laboratories from 1959 to 1981 have shown that the average salinity (wt. % NaCl equivalent, hereinafter termed wt.% eq.) and homogenization temperature (Th), and the ranges of these two parameters for fluid inclusions in sphalerite, quartz, fluorite, and rhodochrosite, respectively, are 8.1 (4.6 - 13.4), 239?C (195-274?C); 6.1 (1.1-10.0), 260?C (190->400?C); 10.7 (6.1-11.1), 217?C (213-229?C) and 260?C (247-268?C) (bimodal distribution of Th); and 9.9 (9.3 - 10.6), 214?C (185-249?C). Inclusions have been measured in minerals from four of the five stages of mineralization previously recognized at Creede. The few inclusions of fluids depositing rhodochrosite (A-stage, earliest in the paragenesis) yield Th and salinity values more similar to those of the low-temperature (average Th 217?C) fluids forming some of the much later fluorite (C-stage) than to any of the other fluids. Th measurements on A-stage quartz range from 192?C to 263?C and average 237?C. The early, fine-grained, B-stage sphalerites yielded Th of 214 to 241?C and salinities of 6.1 to 10.2 wt. % eq. D-stage sphalerite (late in the paragenesis) has been studied in detail (growth-zone by growth-zone) for several localities along the OH vein and reveals a generally positive correlation among Th, salinity and iron content of the host sphalerite. The deposition of D-stage sphalerite was characterized by repeated cycling through different regions of salinity/Th space, as Th and salinity generally decreased with time. Seventeen salinity-Th measurements were made on D-stage sphalerite from one locality on the Bulldog Mountain vein system, which, like the OH vein, is one of four major ore-producing vein systems at Creede. These data suggest a lower Th for a given salinity fluid from sphalerite on the Bulldog Mountain vein than on the OH vein. The very high values of Th for some quartz samples (mostly D-stage) are believed to be a result of the trapping of both gas and liquid from a boiling fluid in the upper levels of the vein system. Boiling of fluids depositing D-stage quartz is indicated by the presence of steam inclusions in quartz and the extreme variability of Th values measured on quartz. The pressure was low (< 125 kg/cm 2) throughout ore deposition. Three major growth zones in D-stage sphalerite are recognized throughout the OH vein. Deposition of the first major zone began from fluids having intermediate salinities and temperatures (7.8-9.2 wt. % eq., 240?C) but the characteristics of the fluids oscillated after that, ranging from 7.2 to 10.1 wt. % eq. and from 225?C to 270?C. Deposition of the second major, most Fe-rich zone began with the hottest, most saline fluids present during D-stage mineralization (. 270?C, 10.5-12.5 wt. % eq., 3 mole % FeS in sphalerite). The fluid then oscillated with respect to Th and salinity (213-274?C, 5.2-12.5 wt. % eq.) but showed a general decrease in both with time. Deposition of the youngest major zone began with a very Fe-poor sphalerite (0.25-0.75 mole % FeS), from the least saline, coolest fluids (5-6.5 wt. % eq., 200-212?C) and ended with a trend of increasing temperature at approximately constant salinity. The fluid-inclusion data can best be explained by a mixing model involving at least two fluids--one hot and saline, the other cool and fresher. Sudden changes in the mixing ratio, presumably from changes in the plumbing, punctuated long periods of remarkably uniform conditions of ore fluid flow and deposition. The effects of other processes such as convection and heat exchange with wall rocks must have been superimposed on this simple mixing model, however. In contrast to an earlier interpretation, several aspects of the inclusion data may be interpreted to suggest exceedingly slow ore deposition. Work in progress may resolve some of these ambiguities and refine
Open-File Report↗
Fluid inclusions in salt from the Rayburn and Vacherie domes, Louisiana
Core samples from the Rayburn and Vacherie salt domes in Louisiana were examined for fluid inclusions, in connection with the possible use of such domes for nuclear waste storage sites. Three types of fluid inclusions were found, brine, compressed gas, and oil (in decreasing volume percent abundance). The total amount of such fluids is small, certainly < 0.1 vol. % and probably in the range 0.01 to 0.001 volume %, but the inclusions are highly erratic in distribution. Unlike many bedded salt deposits, the brine inclusions in this salt contain fluids that are not far from simple NaCl-H2O solutions, with very little of other ions. One of three possible explanations for such fluids is that fresh water penetrated the salt at some unknown time in the past and was trapped; if such entry of fresh water has occurred in the past, it might also occur again in the future.
Open-File Report↗
Fluid-inclusion evidence on the environment of formation of mineral deposits of the southern Appalachian valley
Approximately 1,330 fluid inclusions were studied in samples of ore and gangue minerals from both massive ore and late-stage vugs from a series of Appalachian deposits and five active mines in the East Tennessee zinc districts. Most primary inclusions in sphalerite, fluorite, dolomite, and quartz from East Tennessee homogenized at 82 degrees -149 degrees C. Most primary inclusions in fluorite, barite, and sphalerite from the Central Kentucky, Central Tennessee, and Sweetwater barite districts, ranged from 72 degrees -132 degrees C. Pressure corrections to be added are probably less than 10 degrees C.Freezing data were obtained as a crude measure of the salinity of the inclusion fluids. With few exceptions, all primary inclusions contained very strongly saline brines (mostly >20 weight percent salts), with appreciable amounts of at least some salts other than NaCl, and some contained immiscible globules of oil. The exceptions include several quartz, fluorite, calcite, and barite samples that contained only moderately saline brines (12-16 percent), and some inclusions containing essentially fresh water, in vug calcite. Secondary inclusions had lower salinities than adjacent primaries. Eight primary inclusions in the differently colored outer millimeter of one Central Kentucky fluorite had low salinity (4-6 percent).The data indicate that all these deposits formed from hot, saline brines, with sphalerite forming from slightly hotter and more saline fluids than later gangue minerals. This places severe restrictions on possible modes of origin and makes deeply circulating connate brines the most probable ore fluids. The data give no information on the cause or direction of fluid circulation, which would be controlled by topography, salinity, and temperature during ore deposition, and they permit wide latitude in the construction of possible models. Other observations, on "colloform" textures, seem to indicate the admixture of at least small amounts of surface waters with the brines.
Kentucky, Tennessee, Virginia↗
Fluid inclusion studies on the porphyry-type ore deposits at Bingham, Utah, Butte, Montana, and Climax, Colorado
Data are given on the composition, temperature, pressure, and density of the hydrothermal fluids present in the central Cu-Mo core of the deposit at Bingham, Utah, and in its related but not necessarily coeval peripheral Pb-Zn deposits. These data are based on a study of primary and secondary fluid inclusions in transparent ore and gangue minerals that included the use of freezing, heating, and crushing microscope stages. The composition of the hydrothermal fluids at various stages in the mineralization and repeated later fracturing and rehealing ranged from nearly fresh water to water containing more than 60 weight percent salts in solution--virtually a hydrous saline melt--in some quartz-molybdenite-chalcopyrite veins from the core. Most of these salts have crystallized out as daughter minerals on cooling, forming major amounts of halite and sylvite and minor amounts of anhydrite (?), hematite (?) and several unidentified phases. These highly saline fluids occur only in the core. Some of them have apparently boiled, forming bubbles of a relatively low density CO 2 -rich "steam" containing only a few percent NaCl. These low-density fluids have also been trapped as inclusions. The fluids that formed the peripheral deposits had low salinities, and some of these also have apparently boiled. A few were very high in hydrogen sulfide. Inclusions from a quartz pod and in the quartz-molybdenite-chalcopyrite veins from the core yield the highest temperatures, 640 ° -725 ° C; most inclusions from the core homogenize at temperatures above 400 ° C. Samples from the peripheral deposits were uniformly lower, in the range 294 ° -330 ° C. The abundant evidence of intermittent boiling of these solutions is important because it places limits on the pressure at the time of trapping, it results in there being little or no need for a pressure correction to the homogenization temperatures, and it indicates that the pressure has varied with time. Although some of the homogenization temperatures are very high, the high salinity causes the vapor pressures at homogenization to be relatively low, from about 80 to a maximum of about 1,100 atmospheres. The density of the hydrothermal fluids is of great concern in any consideration of flow patterns, and particularly in the inevitable mixing with possibly heated ground waters. Steam inclusions from the core had gross densities of 0.3 to 0.1 g · cm -3 , but many of the highly saline inclusions in the core contain fluids whose density at trapping was as high as 1.3 g · cm -3 . The fluids trapped in inclusions in the peripheral deposits had densities of 0.75-0.95 g · cm -3 , well below that of the surrounding cold ground water. Hydraulic pressure gradients from these density differences, and the vapor pressures involved, must also have varied with time in any given location, particularly when boiling occurred, and thus the circulation patterns could have been very complex. The more highly saline fluids are believed to be of truly magmatic origin, and not merely heated ground water from the area at the time of the intrusion. The great abundance throughout the core of planes of secondary inclusions in which individual planes are uniform but adjacent planes have widely varying composition, density, and homogenization temperature, is evidence of thorough and repeated fracturing of these rocks under hydrothermal conditions. Inclusions were also examined in some samples from Butte, Montana, Climax, Colorado, and several Arizona porphyry copper deposits. The ranges of temperature, composition, and density found were similar but smaller than at Bingham. This might be simply a result of insufficient sampling.
Arizona, Colorado, Montana, Utah↗
Technique for the extraction and partial chemical analysis of fluid-filled inclusions from minerals
A method has been developed for the extraction and limited chemical analysis of the materials in solution in the fluid from the very minute fluid-filled inclusions such as commonly occur in whitish or milky quartz. The method may also be applied, with some reservations, to a variety of other minerals. As the amounts of substances in the fluid are small compared with possible contaminants, great care is needed in sample purification and cleaning; an electrolytic method has been found to be the only satisfactory final cleaning step. Following this, the inclusions are opened by ball milling of the cleaned sample, with deionized water, in an alumina ball mill using alumina grinding media. The ions present in the resultant slurry are separated from the ground quartz by electrodialysis and analyzed. Other methods, such as the decrepitation of a sample in an absorption train, are used to estimate the amount of H2O and CO2 in the inclusions. The most significant part of the analytical work has been to determine the ratios between the alkali metals. The materials in solution in the fluid-filled inclusions from 11 samples of quartz have been analyzed by the ball milling-electrodialysis method. Although there are large differences between samples, the average weights of the alkali metal ions found, for all samples, in milligrams per kilogram of quartz, are: Li+-0.92, Na+-99, K+-133, Rb+-0.45, Cs+-0.38 (atomic ratios, in the same sequence: 0.03/1.00/0.79/0.001/0.0007). In addition, 27 to 193 milligrams of CI", and 5 to 140 milligrams of SOr were found, per kilogram of quartz. H2O and COa were determined on only one sample. Six of the samples were from gold-quartz veins in the Grass Valley district, California. In these six the Na+/K+ ratios were all very similar, but the amounts of Li+, Rb+ and Cs+ found varied greatly. Although there are serious limitations to this and to all other techniques developed, it is felt that the results presented are sufficiently encouraging to warrant further study and possible application to specific geologic problems, such as the identification of epochs of quartz deposition
Economic Geology↗
Problems in the disposal of acid aluminum nitrate high-level radioactive waste solutions by injection into deep-lying permeable formations
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Trace Elements Investigations↗