Geology topics

I.-M. Chou

Publications and source records attributed to I.-M. Chou.

49 records · Page 3Linked to original sources

USGS1993

Refinement of the evaluation of the role of CO2 in modifying estimates of the pressure of epithermal mineralization

Pressure is the most important of the intensive parameters for relating epithermal mineralization to the geologic setting. This paper describes the limitations on pressure (and therefore depth) of mineralization that may reasonably be derived from simple observations of the behavior of fluid inclusions (i.e., the existence of ice or CO 2 clathrate on the liquidus, the amount of expansion or contraction of the bubble as the host inclusion is crushed in oil on the microscope stage, and the freezing and homogenization temperatures for the inclusion). It is based on the reasonable model that mineralization occurs from a hydrostatically pressured NaCl-CO 2 -H 2 O fluid, consistent with the probability that H 2 O and CO 2 are the only gases contributing significantly to the total pressure. The pressure of CO 2 is, of course, a function of CO 2 content, but, from 100 degrees to 300 degrees C, it is a surprisingly minor function of either temperature or salinity. The presence of the clathrate in freezing studies of fluid inclusions indicates pressures of CO 2 that add at least 1 km to the probable depth of inclusion trapping compared to that estimated from CO 2 -free water. Thus undetected (i.e., no clathrates on cooling) CO 2 in fluid inclusions can nonetheless contribute very significantly to the possible depth of epithermal mineralization. On the other hand, the observation that fluid inclusions crushed in oil have bubbles that do not expand (i.e., <1 atm P (sub CO 2 ) at 25 degrees C), demonstrates CO 2 contents that could add at most a few tens of meters to the depth of mineralization.

Economic Geology↗

USGS1993

A new diamond anvil cell for hydrothermal studies to 2.5 GPa and from -190 to 1200 °C

A new style of diamond anvil cell(DAC) has been designed and built for conducting research in fluids at pressures to 2.5 GPa and temperatures from −190 to 1200 °C. The new DAC has been used for optical microscope observations and synchrotron x‐ray diffraction studies. Fringes produced by interference of laser light reflected from top and bottom anvil faces and from top and bottom sample faces provide a very sensitive means of monitoring the volume of sample chamber and for observing volume and refractive index changes in samples that have resulted from transitions and reactions. X‐ray diffraction patterns of samples under hydrothermal conditions have been made by the energy dispersive method using synchrotron radiation. The new DAC has individual heaters and individual thermocouples for the upper and lower anvils that can be controlled and can maintain temperatures with an accuracy of ±0.5 °C. Low temperatures are achieved by introducing liquid nitrogen directly into the DAC. The equation of state of H 2 O and the α‐β quartz transition are used to determine pressure with an accuracy of ±1% in the aqueous samples. The new DAC has been used to redetermine five isochores of H 2 O as well as the dehydration curves of brucite, Mg(OH) 2 , and muscovite, KAl 2 (Si 3 Al)O 10 (OH) 2 .

Review of Scientific Instruments↗

USGS1992

Speciation in experimental C-O-H fluids produced by the thermal dissociation of oxalic acid dihydrate

Fluid speciations and their related reaction pathways were studied in C-O-H-system fluids produced by the thermal dissociation of oxalic acid dihydrate (OAD: H 2 C 2 O 4 · 2H 2 O) sealed in silica glass capsules. Experiments were conducted in the temperature range 230–750°C, with bulk fluid densities in the range 0.01–0.53 g/cm 3 . Pressure was controlled by temperature and density in the isochoric systems. The quenched products of dissociation experiments were an aqueous liquid and one (supercritical fluid) or, rarely, two (vapor plus liquid) carbonic phase (s). In-situ Raman microanalyses were performed on the quenched carbonic phases at room temperature, at which fluid pressures ranged from about 50 to 340 bars. Bulk fluid speciations were reconstructed from the Raman analyses via mass balance constraints, and appear to monitor the true fluid speciations at run conditions. In experiments from the lowtemperature range (230–350°C), fluid speciations record the dissociation of OAD according to the reaction OAD = CO 2 + CO + 3 H 2 O . A process of the form CO + H 2 O = CO 2 + H 2 is driven to the right with increasing temperature. The hydrogen gas produced tends to escape from the sample systems via diffusion into/through the silica glass capsules, shifting bulk compositions toward equimolar binary H 2 O-CO 2 mixtures. The speciations of fluids in experiments with minimal hydrogen loss show poor agreement with speciations calculated for equilibrium fluids by the corresponding-states model of Saxena and Fei (1988). Such disagreement suggests that the formations of CH 4 and graphite are metastably inhibited in the current experiments, which correlates with their absence or trivial abundances in experimental products. Moreover, calculations in which the stabilities of methane and graphite are suppressed suggest that such metastable equilibrium is approached only in experiments at temperatures greater than about 600–650°C. These results have applications to fluid processes in geological environments, in addition to considerations of using oxalate compounds as volatile sources in experimental studies. It is possible that disequilibrium or metastable fluids may be entrapped as inclusions; re-speciation (toward metastable or stable equilibrium) during P-T evolution of a given terrain would place the fluid inclusion on a new isochore that would not project through the original conditions of entrapment. Moreover, the disequilibrium to metastable nature of dissociation reactions, coupled with the diffusional mobility of hydrogen gas observed in the current experiments, suggests that the predominance of binary H 2 O-CO 2 fluid mixtures in natural inclusions from medium- to high-grade metamorphic terrains may be more than a coincidence of similar initial bulk compositions.

Geochimica et Cosmochimica Acta↗

USGS1992

Phase relations in the system NaCl-KCl-H2O: V. Thermodynamic-PTX analysis of solid-liquid equilibria at high temperatures and pressures

The Gibbs energies of mixing for NaCl-KCl binary solids and liquids and solid-saturated NaCl-KCl-H 2 O ternary liquids were modeled using asymmetric Margules treatments. The coefficients of the expressions were calibrated using an extensive array of binary solvus and solidus data, and both binary and ternary liquidus data. Over the PTX range considered, the system exhibits complete liquid miscibility among all three components and extensive solid solution along the anhydrous binary. Solid-liquid and solid-solid phase equilibria were calculated by using the resulting equations and invoking the equality of chemical potentials of NaCl and KCl between appropriate phases at equilibrium. The equations reproduce the ternary liquidus and predict activity coefficients for NaCl and KCl components in the aqueous liquid under solid-saturation conditions between 673 and 1200 K from vapor saturation up to 5 kbar. In the NaCl-KCl anhydrous binary system, the equations describe phase equilibria and predict activity coefficients of the salt components for all stable compositions of solid and liquid phases between room temperature and 1200 K and from 1 bar to 5 kbar.

Geochimica et Cosmochimica Acta↗

USGS1991

Geology and geochemistry of three sedimentary-rock-hosted disseminated gold deposits in Guizhou Province, People's Republic of China

Five sedimentary-rock-hosted disseminated gold deposits have been discovered since 1980 in southwestern Guizhou Province (PRC). Submicron-sized gold is disseminated in silty carbonate and carbonaceous shale host rocks of Permian and Triassic age. Arsenic, antimony, mercury, and thallium accompany the gold. Associated hydrothermal alteration resulted in decarbonatization of limestone, silicification, and argillization, and depletion of base metals, barium, and many other elements. Organic material occurs in most host rocks and ores. It was apparently devolatilized during a regional heating event that preceded hydrothermal activity, and thus was not mobilized during mineralization, and did not affect gold deposition. The geologic setting of the Guizhou deposits includes many features that are similar to those of sedimentary-rock-hosted deposits of the Great Basin, western United States. The heavy-element suite that accompanies gold is the same, but base metals are even scarcer in the Guizhou deposits than they are in U.S. deposits. The Guizhou deposits discovered to date are smaller than most U.S. deposits and have no known spatially associated igneous rocks.

Guizhou Province↗

USGS1987

Products of hexachlorocyclopentadiene (C-56) in aqueous solution

The photodegradation and degradation products of hexachlorocyclopentadiene (C-56) in aqueous solutions were studied in the laboratory. In each case, the half-life of C-56 was less than 4 min when exposed to sunlight. At least eight degradation products were positively or tentatively identified: 2,3,4,4,5-Pentachloro-2-cyclopentenone, hexachloro-2-cyclopentenone and hexachloro-3-cyclopentenone were the primary photodegradation products, and pentachloro- cis -2,4-pentadienoic acid, Z- and E-pentachlorobutadiene and tetrachlorobutyne were the secondary degradation products. Dissociation of the primary photolysis products may proceed through corresponding pentadienoic acids to form smaller molecular weight compounds such as pentachlorobutadiene isomers and tetrachlorobutyne. In addition, dimerization of 2,3,4,4,5-pentachloro-2-cyclopentenone to form higher molecular weight compounds such as hexachloroindenone may present a minor route of degradation. The results also indicate that C-56 is highly photoreactive and suggest a possible pathway for the compound's transformation in the environment when exposed to sunlight.

Environmental Toxicology and Chemistry↗

USGS1987

Phase relations in the system NaCl-KCl-H 2 O. III: Solubilities of halite in vapor-saturated liquids above 445°C and redetermination of phase equilibrium properties in the system NaCl-H 2 O to 1000°C and 1500 bars

Halite solubilities along the three-phase curve in the binary system NaCl-H 2 O determined by DTA experiment can be represented by the equation Wt.% NaCl (±0.2) = 19.39 − 0.0364 t + 3.553 × 10 −4 T 2 − 2.298 × 10 −7 T 3 , where 447≦ T ≦ 800° C . Even though these halite solubilities are up to ~7 wt.% higher than those reported in literature, extrapolated values at temperatures below 447°C merge with the literature values. It is considered that the equation adequately describes halite solubilities between 382 and 800°C. The newly established solubility data are believed to be more reliable because they are compatible with data obtained by using synthetic fluid inclusions and with the observed DTA signals and also because they were measured in a relatively corrosion-free system. In an earlier publication (GUNTER et al ., 1983), we were puzzled greatly by multiple and rather unreproducible DTA peaks appearing during isobaric cooling (heating experiments were nondefinitive) at pressures below about 500 bars. These DTA signals apparently suggested that the “halite liquidus” swung sharply upward in temperature as pressure decreased from about 500 bars to that of the halite-saturated boiling curve. Further analysis of the data and helpful discussions with several individuals have revealed that the behavior is a consequence of the initial (precooling) separation of the fluid into NaCl-poor gas and NaCl-rich liquid that failed to homogenize in the short time encompassed by the DTA experiments. The present analysis is based on extrapolations of the slopes from pressures above 500 bars. Through use of these new halite solubility data and the data from synthetic fluid inclusions [formed by healing fractures in inclusion-free Brazilian quartz in the presence of two coexisting, immiscible NaCl-H 2 O fluids at various temperatures and pressures (Bodnar et al ., 1985)], phase equilibria in the system NaCl-H 2 O have been redetermined to 1000°C and 1500 bars.

Geochimica et Cosmochimica Acta↗

USGS1986

New aromatic biomarkers and possible maturity indicators found in New Albany Shale extracts

Aromatic hydrocarbons from benzene extracts of New Albany Shale were characterized. A biomarker that has a molecular weight of 546 and a structural configuration consistent with that of an alkyl-aromatic hydrocarbon (C 40 H 66 ) was tentatively identified. It was found that the relative concentrations of the biomarker are indicative of differing levels of thermal maturity of the shale organic matter. A 40-carbon bicyclic carotenoid (C 40 H 48 ) is proposed as the geochemical precursor of this biomarker. Thermal maturity of the shale organic matter can also be differentiated by observing differences in “fingerprints” as obtained by field-ionization mass spectrometry on the aromatic hydrocarbon fraction. Using this technique, we found that the more mature shale samples from southeastern Illinois contain more low molecular weight extractable aromatic hydrocarbons and the less mature shale samples from northwestern Illinois contain more high molecular weight extractable aromatic hydrocarbons. It was demonstrated that field-ionization and tandem mass spectrometric techniques through fingerprint and individual compound identification, are useful for shale aromatic hydrocarbon fraction characterization and for thermal maturation interpretation.

Illinois↗

USGS1986

Permeability of precious metals to hydrogen at 2kb total pressure and elevated temperatures

No abstract available.

American Journal of Science↗

USGS1985

Sulphur in char and char desulphurization by acid leaching and hydropyrolysis

Sulphur compounds volatilized during pyrolysis of acid-leached char were measured to determine characteristics of char desulphurization reactions. Pyrolysis of char in a hydrogen atmosphere (hydropyrolysis) produced a much higher concentration of thiophenic organics compared with that produced during pyrolysis in a nitrogen atmosphere. Hydrogen sulphide gas evolution, at progressively increasing pyrolysis temperature in a helium atmosphere, was measured on five char samples: untreated char, hydrochloric acid-leached char, and three model chars: a demineralized char and two demineralized chars incorporated with sulphur via reactions with elemental sulphur. Hydrogen sulphide gas evolution in untreated char and acid-leached char was found to peak in three temperature regions; the maxima are thought to relate to sulphur in different bonding environments. The amounts of hydrogen sulphide volatilized were much higher for acid-leached char than for untreated char. The gas evolved from each of the remaining three samples showed a single peak region corresponding closely to one of the three peak regions observed for the first two chars. The results of this study indicate that elemental sulphur was produced during hydrochloric acid leaching of the untreated char and suggested that the improved rate of desulphurization observed in the char that had been acid-leached before hydropyrolysis was due in part to the conversion of strongly bound mineral sulphur forms to more weakly bound sulphur forms that are predominantly elemental sulphur in character, and are more easily removed by hydrogen.

Fuel↗

USGS1985

Organic geochemical characterization of the New Albany Shale group in the Illinois Basin

Benzene extractable aliphatic hydrocarbons from the New Albany Shale in the Illinois Basin were characterized by gas chromatography and mass spectrometry, and the total organic matter of the shale was characterized by solid state carbon-13 cross polarization magic angle spinning nuclear magnetic resonance. Core samples from a northwest-trending cross-section of the Illinois Basin were studied. Gas chromatography (GC) and gas chromatography-mass spectrometric analysis (GC/MS) data indicate a regional variation of the aliphatic composition of the shale extracts. A positive, linear relationship between the two ratios, pristane/ n -C 17 and phytane/ n -C 18 , is indicated. The NMR results indicated that organic matter deposited in northwestern Illinois shale is relatively high in aliphatic hydrocarbon content while, in contrast, organic matter found in southeastern Illinois shale is relatively low in aliphatic hydrocarbon content. Our findings suggest that the organic variation of the shale is mainly due to the differences in thermal maturity of the shale organic matter and the use of pristane/ n -C 17 ratio as a thermal parameter in the study of oil may be extended to the study of the ancient sediments.

Illinois, Indiana, Kentucky↗

USGS1983

Phase relations in the system NaCl-KCl-H 2 O II: Differential thermal analysis of the halite liquidus in the NaCl-H 2 O binary above 450°c

Thermal analysis of the halite liquidus in the system NaCl-H 2 O has been conducted for NaCl mole fractions ( X NaCl ) greater than 0.25 ( i.e. , > 50 wt. % NaCl) at pressures between 0.3 and 4.1 kb and temperatures greater than 450°C. The position of the liquidus was located by differential thermal analysis (DTA) of cooling scans only, as heating scans did not produce definitive DTA peaks. The dP/dT slope of the liquidus is positive and steep at high pressures, but at high X NaCl , and pressures below 0.5 kb it appears to reverse slope and intersects the three-phase curve (liquid-halite-vapour) at a shallow angle. However, due to the complex nature of the DTA signal when P <- 0.5 kb, there is considerable doubt about exactly what event has been recorded in the experiments conducted at these low pressures. The solubility of halite can be expressed as a function of the mole-fractional-based activity of NaCl in the liquid phase ( L ) in temperature (T, °K) and pressure (P, bars) In Our liquidus data (based on 10 compositions) above 500 bars for these brines were combined with this equation to generate activity coefficients of NaCl which were fit within their experimental uncertainties to the following one parameter Margules equation In . Concentrated solutions of NaCl show negative deviations from ideality which rapidly increase in magnitude with decreasing X NaCl .

Geochimica et Cosmochimica Acta↗

USGS1982

Phase relations in the system NaCl-KCl-H2O. Part I: Differential thermal analysis of the NaCl-KCl liquidas at 1 atmosphere and 500, 1000, 1500, and 2000 bars

A simple differential thermal analysis (DTA) technique has been developed to study phase relations of various chemical systems at elevated pressures and temperatures. The DTA system has been calibrated against known melting temperatures in the system NaCl-KCl. Isobaric sections of the liquidus in the system NaCl-KCl have been determined at pressures of 1 atmosphere and 500, 1000, 1500, and 2000 bars. Using the least-squares method, the following equation was used to fit the experimental data: T(°C)= ∑ i=0 6 a i X i KCl "> T(°C)=∑i=06a i X i KCl where T is the liquidus temperature, X KCl is mole fraction of KCl, and a i (listed below) are the derived empirical constants. P (bars) a o "> ao a 1 "> a1 a 2 "> a2 a 3 "> a3 a 4 "> a4 a 5 "> a5 a 6 "> a6 1 atm. 800.1 −334.2 781.6 −6490.3 17553.1 −17638.4 6098.3 500 813.5 −354.9 743.3 −6011.7 16406.4 −16516.3 5702.8 1000 824.5 −406.7 1446.8 −8818.4 21253.5 −20343.7 6839.4 1500 838.6 −418.7 1434.7 −8819.0 21557.9 −20908.4 7123.1 2000 848.5 −381.5 1246.9 −8605.0 21785.8 −21449.1 7375.8 The liquidus temperatures estimated from these equations are within ±3°C of experimental values. The measured liquidus temperatures at 1 atmosphere agree with the best available data to within 5°C. The melting temperatures for pure end members at higher pressures agree with the values calculated from the Simon equation (Clark, 1959) to within 3°C. No previous melting data are available for the intermediate compositions at elevated pressures. Using the data in both heating and cooling scans, the minimum melting temperature at 1 atmosphere in the system was located at 658° ± 3° C where the sample has an equimolar composition.

Geochimica et Cosmochimica Acta↗