Geology topics

E. Roedder

Publications and source records attributed to E. Roedder.

31 records · Page 2Linked to original sources

USGS1972

Occurrence of chromian, hercynitic spinel ("pleonaste") in Apollo-14 samples and its petrologic implications

Many isolated grains of a reddish pleonaste-type spinel occur in fines and metabreccia samples, particularly 14 319. Electron microprobe analyses (104) of spinels and their associated phases include 58 of pleonaste which show Mg/(Mg + Fe) 0.44–0.62 and Cr/(Cr + Al) 0.017–0.134 (atomic), plus minor amounts of other ions, and differ greatly from almost all previously recorded lunar spinels; almost no spinels of intermediate composition were found. Two types of compositional zoning exist: a diffuse primary one with cores lower in Ti, and a narrow secondary one from reaction with matrix yielding rims higher in Cr, Ti, and Mn. At contacts with breccia matrix there is a narrow corona of almost pure plagioclase (An 80 -An 94 ), free of opaque minerals and pyroxene. Two types of solid inclusions found in the pleonaste are calcic plagioclase, and tiny spherical masses of nickel-rich sulfide. Similar pleonaste occurs in crystalline rock clasts, mainly with plagioclase; one clast (A) consists only of coarse olivine, plagioclase, and pleonaste, with granulated grain boundaries suggestive of deformation. From composition and texture, this clast is one possible candidate for the mafic cumulate counterpart of the “anorthositic” crust. Another clast (B), also made solely of olivine, plagioclase and pleonaste, is itself a breccia. These data suggest a two-stage brecciation process: 1) disruption (probably pre-Imbrian) of a deep-seated pleonaste-bearing source rock like A and reconsolidation to form a breccia without addition of pyroxene, ilmenite or other minerals; and 2) disruption of this breccia to yield breccia clast B which was then incorporated into the Fra Mauro formation.

Earth and Planetary Science Letters↗

USGS1972

Silicate melt inclusions and glasses in lunar soil fragments from the Luna 16 core sample

More than 2000 fragments were studied microscopically, and electron microprobe analyses were made of 39 selected areas, from a few square mm of polished surface, through 75- to 425-μm fragments of lunar soil from two samples of the Luna 16 core. The silicate melt inclusions and glasses differ in important details from those observed earlier in the Apollo samples. Melt inclusions in olivine contain epitaxially oriented daughter crystals, but also show a similar epitaxy around the outside of the crystals not observed in previous lunar samples. Melt inclusions in ilmenite suggest trapping at successive stages in a differentiation sequence. There is abundant evidence for late-stage silicate liquid immiscibility, with melt compositions similar but not identical to those from Apollo 11 and 12. A comparison of the alkali ratio of any given bulk rock analysis with that of its late-stage, high-silica melt shows gross differences for different rocks. This is pertinent to understanding late-stage differentiation processes. Glass fragments and spherules exhibit a wide range of crystallization textures, reflecting their wide range of compositions and cooling histories. No significant differences were found between the two portions of core examined (Zones A and D).

Earth and Planetary Science Letters↗

USGS1971

Fluid inclusions in quartz crystals from South-West Africa

Quartz crystals from calcite veins of unknown age in Precambrian metasedimentary rocks at Geiaus No. 6 and Aukam farms in South-West Africa contain both primary and secondary inclusions filled with one or a variable combination of: organic liquid, moderately saline aqueous liquid, dark-colored solid, and vapor. Analysis of these materials by microscopy and by gas chromatography and mass spectrometry shows the presence of constituents of both low and high molecular weights. The former include CH 4 , C 2 H 6 , C 3 H 8 and possibly C 4 H 10 as well as CO, CO 2 , H 2 O, N 2 and H 2 . High molecular weight components are dominantly n-alkanes and isoprenoid hydrocarbons. The n-alkanes range from at least n-C 10 to n-C 33 . Concentrations of n-alkanes larger than n-C 17 decrease regularly with increasing carbon number. An homologous series of isoprenoid hydrocarbons ranging from at least C 14 to C 20 is present in unusually high concentrations. Pristane (C 19 ) is most abundant, and C 17 isoprenoid is least abundant. The molecular composition and distribution of hydrocarbons suggest biological precursors for these components. Consideration of data provided by freezing, crushing and heating experiments suggests that the pressures at the time these in part supercritical fluids were trapped probably exceeded 30–40 atm, and the minimum trapping temperature was about 120–160°C. Both primary and secondary inclusions apparently containing only organic materials were trapped by the growth of the host quartz from aqueous solution. The data obtained neither prove nor preclude Precambrian, Paleozoic or younger sources for the organic materials.

Geochimica et Cosmochimica Acta↗

USGS1968

Experimental evidence that fluid inclusions do not leak

The possibility of leakage of fluids into or out of fluid inclusions subjected to large pressure gradients has always been considered a serious problem in the interpretation of inclusion data. As previous experimental evidence on leakage was contradictory, new experiments were performed. Inclusion vapor bubble diameters in twelve quartz crystals (≤ 3 mm; 8 localities), not sawn, ground or polished, were measured. The samples were run at Pa-.o,-4,000 bars, at T u 100°-410° C, for ≤ 17 days total, and remeasured after each run. Similar experiments at ≤ 155° C were made on sphalerite and calcite. Most inclusions in most samples (even those only 5am under the surface in quartz) showed no change in bubble diameter, hence no leakage. A few exceptions, mainly among inclusions homogenizing at T « Tru, had P internal » P internal , hence they ruptured and lost liquid during the 410° C run. From this work and a review of the literature, we conclude that most inclusions have not suffered major leakage. Some previous experiments indicating leakage may be explained by microfractures introduced during sample preparation. The present work does not , however, preclude the possibility of diffusion of small but chemically significant amounts of substances such as hydrogen in or out of inclusions .

Economic Geology↗

USGS1968

Temperature, salinity, and origin of the ore-forming fluids at Pine Point, Northwest Territories, Canada, from fluid inclusion studies

Although the Pine Point ore is relatively poor in useable fluid inclusions, some sphalerite crystals from replacements, vugs, and from " colloform" crusts were found to contain primary or pseudosecondary liquid-gas inclusions adequate for study . Most (132 of 133) of these had low freezing temperatures, indicating exceedingly saline brines. The 112 inclusions suitable for filling- temperature determination homogenized at +51° to +97° C. A very small pressure correction must be added to obtain the trapping temperature .Dolomite crystals from some of the same vugs contain large numbers of primary inclusions, many of which have leaked. The twenty-three that presumably have not leaked had filling temperatures of 90°-100° C, but somewhat lower salinities. Inclusions in late calcite appeared to have similar gas-liquid ratios, but had still lower salinities.The significance of these data lies in the limitations they place on the choice of possible mechanisms of origin of these large deposits. This choice, in turn, may influence the success in prospecting for blind ore bodies. There is general agreement that the deposits are of Mississippi Valley type. Although the high salinities may reflect solution of salts from evaporites, as are now found to the south, the elevated temperatures seem to require deep circulation, perhaps through known faults in the underlying Pre-cambrian. The densities of these brines, even at their elevated temperatures, are well above that of fresh, cold surface water, thus restricting the possible modes of circulation during ore deposition.

northwest Canada↗

USGS1968

The non-colloidal origin of 'colloform' textures in sphalerite ores

" Colloform " ores have generally been considered to have been deposited as colloidal sulfide gels, and even transported as colloidal "sols." However, studies of doubly polished plates of " colloform " sphalerite -wurtzite assemblages from various deposits reveal crystal growth features that cannot have been formed by crystallization from gels, and indicate that most, and perhaps all, grew directly as minute druses of continuously euhedral crystals projecting into an ore fluid. Each of the many textural criteria proposed for recognizing colloidal deposition is shown to be invalid, ambiguous, or inapplicable to these samples, and perhaps also to most other " colloform " mineral samples.Four conclusions pertinent to ore research are derived from this study: (1) Primary fluid inclusions in " colloform " samples are believed to represent the original ore fluid, not merely a residual fluid from the crystallization of a gel. (2) Although euhedral crystals may possibly grow directly from a sol, several features make a noncolloidal (true solution) ore fluid more probable. (3) Maintenance of the large number of crystal nuclei responsible for the " colloform " texture is attributed to relatively high supersaturation, and hence relatively high nucleation and growth rates, for the temperatures involved. (4) Remarkably uniform, regular compositional microbands, traversing many crystals in samples from the east Tennessee, Aachen, and particularly the Pine Point deposits, are tentatively interpreted as annual "varves." No actual growth rates have been determined, but each "varve" consists of a dark and a light band, outlining sharply euhedral former crystal growth patterns and suggesting an annual change in the ore fluid due to dilution with surface waters of varying volume or chemistry (e.g., oxygen or organic content).

Economic Geology↗

USGS1968

Environment of ore deposition at the Mex-Tex deposits, Hansonburg District, New Mexico, from studies of fluid inclusions

These deposits , in Pennsylvanian limestone and shale, contain barite, fluorite, low-silver galena with "J-type" lead, and quartz, and only minor amounts of other minerals. Mineralization occurs in veins, in blankets of bedded, rhythmically banded "coontail" ore , and in vuggy, coarsely crystalline open-space fillings in tectonic and solution channels in limestone adjacent to faults. Except for widespread silicification, the mineralization is very similar to that of the southern Illinois deposits . The main stages of hypogene mineralization are: 1) sphalerite, pyrite, galena and chalcopyrite; 2) five easily recognizable substages of fluorite with intermittent quartz and barite; and 3) late calcite.More than 500 primary and 2,500 pseudosecondary inclusions , mainly from fluorite, were studied on the freezing and heating microscope stages. Some primary inclusions contain organic matter. Gross supercooling indicates slow ore - fluid movement. Recognizable planes of pseudo-secondaries (each containing 20-200 inclusions ) yield data essentially identical with coeval primaries, but the few planes of presumed secondaries do not.The first three substages of fluorite formed from fluids that were essentially constant in temperature at 186°-205° C (assumed pressure correction +10° C), but increased in salinity from aproximately 10 up to 15 weight percent salts. Succeeding substages formed at gradually decreasing temperatures (to about 140° C) and increasing salinity (maximum 17%), with breaks marking several individual substages. A few inclusions in an early barite have anomalously low homogenization temperatures. Coarse selenite has primary inclusions full of fresh water and hence is presumed to be supergene.These data do not prove any given theory or origin for the fluids or the deposits , but they do place some limits on possible mechanisms of origin.

New Mexico↗

USGS1967

Metastable superheated ice in liquid-water inclusions under high negative pressure

In some microscopic inclusions (consisting of aqueous liquid and vapor) in minerals, freezing eliminates the vapor phase because of greater volume occupied by the resulting ice. When vapor fails to nucleate again on partial melting, the resulting negative pressure (hydrostatic tension) inside the inclusions permits the existence of ice I crystals under reversible, metastable equilibrium, at temperatures as high as +6.5°C and negative pressures possibly exceeding 1000 bars.

Science↗

USGS1965

Report on S.E.G. Symposium on the chemistry of the ore-forming fluids August-September,1964

Sessions included presentations and discussions of the following topics: mineral stability and phase assemblages at ore - forming temperatures and pressures; high-temperature solution chemistry of sulfides, carbonates, and silicates, with consideration of complexing and stability, and the generation of ore fluids ; hydrothermal fluids as deduced from wallrock alteration, from fluid inclusions and hot springs, from isotopic studies, and from mine studies, zoning, and so forth.

Economic Geology↗

USGS1963

Studies of fluid inclusions iii: Extraction and uantitative analysis of inclusions in the milligram range

A method has been developed for the extraction and chemical microanalysis of individual fluid inclusions , or groups of inclusions , in the milligram range . Usable quantitative analyses for Na, K, Ca, Mg, CI, B, and SO* have been obtained of mineral samples containing several milligrams of inclusion fluid , and with increased experimental errors, on fractional milligram samples. The steps involved are: 1) concentration of inclusions by sample selection and cutting; 2) electrolytic cleaning; 3) crushing in soft copper sample tube in vacuo; 4) conversion of emitted water to hydrogen and determination of its volume; 5) mass spectrometric determination of the D/H ratio if desired; 6) leaching of the crushed mineral to dissolve soluble salts remaining; 7) microanalysis of the filtrate by sensitive colorimetric and flame photometric methods. The method has been applied to determine the composition of fluid inclusions in mineral samples from several types of deposits, with special attention to a series of samples from Mississippi Valley-type ore deposits.

Economic Geology↗

USGS1963

Studies of fluid inclusions; [Part] 2, Freezing data and their interpretation

Aqueous and non-aqueous inclusions in 84 samples of various minerals from a wide range of geologic environments were studied with the freezing stage in order to gain an insight into the range of concentrations and compositions of fluid inclusions . Inclusions in most Mississippi Valley-type ore minerals contain highly concentrated saline solutions, showing freezing temperatures between -23.4° and -10.5° C; minerals from ore deposits of more typically hydrothermal affiliations mainly show temperatures of -9.4° to nearly 0° C; and inclusions in quartz crystals from sedimentary, metamorphic, and igneous rock environments show a wide range of freezing temperatures. Inclusions in pegmatite minerals in particular vary over a wide range, from the most concentrated solutions found in any inclusion (> 40% salts) to fairly dilute solutions (< 5% salts). Most inclusions in quartz from Swiss Alpine-type veins, and from Brazilian quartz veins and pegmatites, show freezing temperatures in the range -8.5° to - 2 .5°, and considerable free C02. Other geologic environments sampled include Colombian emerald, pegmatitic topaz and fluorite, the Triassic traprock zeolite assemblage, and sedimentary halite beds. Not all the phenomena exhibited by inclusions at low temperature are completely understood at present but several crystalline hydrate phases, such as NaCl-2H,0 and CO,-5%H,0 (structural formula 8C02-46H20), are shown to be stable in inclusions of appropriate composition even at temperatures above 0° C, and probably exist in the inclusions in natural rocks in polar regions. More significantly, the formation and recognition of such phases aid in establishing the gross composition of individual inclusions far too small for chemical analysis. The data obtained are useful in a variety of ways, such as: discriminating among gas, liquid, and supercritical fluid , and among liquid water, liquid oil, and liquid C02 in inclusions ; improving precision of the pressure corrections applied to inclusion filling temperature determinations; proving the general lack of leakage into or out of inclusions ; estimating the minimum pressure at the time of deposition of certain samples; verifying the lack of extraneous solid crystallization nuclei in the inclusions and hence their formation from exceedingly quiet, clean solutions; determining the total equivalent NaCl concentrations and some information concerning the composition of the fluids from which ores have formed; and determining changes in the composition of the fluids bathing a single crystal during its growth, and at certain times throughout its history.

Economic Geology↗

USGS1963

Neutron activation analysis of fluid inclusions for copper, manganese, and zinc

Microgram quantities of copper, manganese, and zinc, corresponding to concentrations greater than 100 parts per million, were found in milligram quantities of primary inclusion fluid extracted from samples of quartz and fluorite from two types of ore deposits. The results indicate that neutron activation is a useful analytical method for studying the content of heavy metal in fluid inclusions.

Science↗

USGS1962

Studies of fluid inclusions I: Low temperature application of a dual-purpose freezing and heating stage

The design and operation of a microscope freezing stage developed for use at magnifications up to 500X are described. It makes possible studies of low - temperature phase changes such as the freezing of a saline water phase, and hence an estimate of the total salt concentration, in fluid inclusions as small as 10 microns (10-6 milligram in weight). The crystal or polished mineral plate containing the inclusions is viewed while immersed in a thermostated heat exchange medium (acetone) circulating rapidly in order to minimize thermal gradients. The stage permits easy operation at temperatures down to -35° C, with electrical control to ±0.05° C, and to much lower temperatures with manual control. With substitution of silicone oil for acetone, the same stage can be used for heating experiments up to +250° C. Calibration points in the low range indicate the accuracy of freezing temperature determinations on optimum material to be better than ±0.1° C. The low relief of ice crystals in water solution places considerable importance on sample selection, preparation, and lighting. As a result of almost ubiquitous and drastic supercooling (meta-stability), -35° C is inadequate to freeze most inclusions . Holding at -78.5° C (acetone + solid CO 2 ) for thirty minutes is generally adequate, although a few samples require extended immersion in liquid nitrogen at -196° C to cause freezing of even a part of their inclusions . Such extensive supercooling is not possible with most surface waters owing to the presence of abundant extraneous solid nuclei for the crystallization of ice.

Economic Geology↗