Geology topics

G.L. Cygan

Publications and source records attributed to G.L. Cygan.

7 recordsLinked to original sources

USGS2000

Geology, hydrology, and ground-water quality of the upper part of the Galena-Platteville aquifer at the Parson's Casket Hardware Superfund site in Belvidere, Illinois

The geology, hydrology, hydraulic properties, and distribution of contaminants in the upper part of the Galena-Platteville aquifer at the Parson's Casket Hardware Superfund site in Belvidere, Illinois, were characterized on the basis of data collected from boreholes by use of packer assemblies, flowmeter logging, and borehole ground-penetrating radar. Four permeable intervals were identified in the upper part of the Galena-Platteville aquifer: (1) a shallow, subhorizontal fracture from 37 to 40 feet below land surface; (2) an inclined fracture from 75 to 85 feet; (3) a shallow, vuggy interval from 90 to 100 feet; and (4) a deep, vuggy interval from about 140 to 180 feet. The calculated horizontal hydraulic conductivity of the two fractured intervals exceeds 50 feet per day and is more than an order of magnitude greater than that of the vuggy intervals. Water levels in the Galena-Platteville aquifer respond to pumping cycles in the Belvidere municipal-supply wells below a depth of at least 180 feet. Results of flowmeter logging and constant discharge aquifer testing indicate that the shallow, subhorizontal fracture is hydraulically connected to the overlying unconsolidated aquifer. Discrete inclined fractures are the primary conduits for vertical ground-water flow between the permeable units within the upper part of the Galena-Platteville aquifer, and perhaps for flow to the deeper parts of the aquifer. The inclined fractures may become less permeable with depth. A maximum effective porosity in the deep, vuggy interval of 8.8 percent was calculated from hydrologic and borehole radar-tomography data collected during tracer testing. The average maximum horizontal ground-water velocity through this interval was calculated at 21.4 feet per day using cross-hole radar tomography under a hydraulic gradient of 1.25 feet per foot. Trichloroethene, trichloroethane, and tetrachloroethene are the primary volatile organic compounds detected in the aquifer. There is no distinct pattern of the concentration of volatile organic compounds with depth; however, the highest concentrations tend to be present in the shallow part of the aquifer at the site. Movement of organic compounds through vertical fractures may account for their presence in the deeper parts of the aquifer.

Illinois↗

USGS1994

An experimental study of zinc chloride speciation from 300 to 600 °C and 0.5 to 2.0 kbar in buffered hydrothermal solutions

The solubility of sphalerite (ZnS) was measured in KCl-HCl-H 2 O solutions at 300–600°C and 0.5–2.0 kbar. The silicate assemblage K-feldspar-muscovite (or andalusite)-quartz was used to buffer the solution to acid conditions, resulting in the total solubility reaction 2 K + + KAl 2 AlSi 3 O 10 ( OH ) 2 + 6 SiO 2 + ZnS + nCl − = ZnCl n (2− n ) + 3 KAlSi 3 O 8 + H 2 S . (muscovite) (quartz) (sphalerite) (K-feldspar) A computer retrieval technique was used to derive average chloride ligand numbers for chlorozinc species at 0.25–2.0 molal total chloride. This technique mathematically solves for the average ligand number using a series of pertinent chemical relations at P and T . Mono- and di-chlorozinc species were found to predominate throughout the pressure-temperature-composition range investigated. The logarithms of the first and second dissociation constants for ZnCl 2 0 were evaluated over the P - T range; for example, at 1 kbar, the values −0.41 and −1.42 were computed for the logarithm of the first dissociation constant, while −7.62 and −10.57 were computed for the logarithm of the second dissociation constant, for 400 and 500°C, respectively. Results are compared to past studies conducted at subcritical conditions and differ in that we find no evidence for more highly coordinated chloro-zinc species except possibly for ZnCl 3 − at 600°C, 1 and 2 kbar. Our results are consistent with electrostatic theory, which favors lower charged to neutral molecules in low dielectric-constant media.

Geochimica et Cosmochimica Acta↗

USGS1993

Rare earth element concentrations in geological and synthetic samples using synchrotron X-ray fluorescence analysis

The concentrations of rare earth elements (REEs) in specific mineral grains from the Bayan Obo ore deposit and synthetic high-silica glass samples have been measured by synchrotron X-ray fluorescence (SXRF) analysis using excitation of the REE K lines between 33 and 63 keV. Because SXRF, a nondestructive analytical technique, has much lower minimum detection limits (MDLs) for REEs, it is an important device that extends the in situ analytical capability of electron probe microanalysis (EPMA). The distribution of trace amounts of REEs in common rock-forming minerals, as well as in REE minerals and minerals having minor quantities of REEs, can be analyzed with SXRF. Synchrotron radiation from a bending magnet and a wiggler source at the National Synchrotron Light Source, Brookhaven National Laboratory, was used to excite the REEs. MDLs of 6 ppm (La) to 26 ppm (Lu) for 3600 s in 60-??m-thick standard samples were obtained with a 25-??m diameter wiggler beam. The MDLs for the light REEs were a factor of 10-20 lower than the MDLs obtained with a bending magnet beam. The SXRF REE concentrations in mineral grains greater than 25 ??m compared favorably with measurements using EPMA. Because EPMA offered REE MDLs as low as several hundred ppm, the comparison was limited to the abundant light REEs (La, Ce, Pr, Nd). For trace values of medium and heavy REEs, the SXRF concentrations were in good agreement with measurements using instrumental neutron activation analysis (INAA), a bulk analysis technique. ?? 1993.

Nuclear Instruments and Methods in Physics Researc↗

USGS1992

Hydrothermal ore-forming processes in the light of studies in rock- buffered systems: I. Iron-copper-zinc-lead sulfide solubility relations

Experimental studies, using cold-seal and extraction vessel techniques, were conducted on Fe, Pb, Zn, and Cu sulfide solubilities in chloride solutions at temperatures from 300 degrees to 700 degrees C and pressures from 0.5 to 2 kbars. The solutions were buffered in pH by a quartz monzonite and the pure potassium feldspar-muscovite-quartz assemblage and in f (sub S 2 ) - f (sub O 2 ) largely by the assemblage pyrite-pyrrhotite-magnetite. Solubilities increase with increasing temperature and total chloride, and decrease with increasing pressure. The rise in solubility is particularly steep between 300 degrees and 500 degrees C and between 1,000 and 500 bars. With increasing temperature at any given pressure, or with decreasing pressure at any given temperature, metal solubility eventually passes through a maximum due to increasing competition for chloride by the alkali, hydrogen, and base metal ions and because intersection with a two-fluid region eventually occurs. In that portion of the two-fluid region encountered in the study, metal solubilities in the brine were very high, but solubilities in the gas phase also were significant. In a system controlled by the potassium feldspar-muscovite-quartz buffer, 1-m total Cl (super -) , and the assemblage pyrite-pyrrhotite-magnetite-sphalerite-galena-chalcopyrite, solubilities in ppm at 1 kbar and 300 degrees , 400 degrees , and 500 degrees C were 237, 1,216, and 5,636, for Fe; 51, 613, and 3,105 for Pb; 36, 423, and 2,649 for Zn; and 11, 40, and 113 for Cu, respectively. At 400 degrees C, 0.5 and 2 kbars, the values were 2,627 and 500 for Fe; 1,262 and 194 for Pb; 983 and 120 for Zn; and 60 and 29 for Cu, respectively. All of the above were in the single-fluid region. Single-metal solubilities also were investigated to assess the influence of iron on the solubility of the other metals and to corroborate preliminary dissociation constants for the metal chloride complexes involved. The effect of increasing chloride concentration on solubility reflects primarily a shift to lower pH via the silicate buffer reactions. The effect of decreasing pressure reflects primarily the relative change in the dissociation constants of the chloride complexes involved. Increasing sulfur fugacity lowers solubility, but in systems controlled at relatively low values by an f (sub S 2 ) buffer or wall-rock sulfidation reactions, solutions of high metal content relative to reduced sulfur will tend to develop at high chloride concentrations. Similarity in behavior with respect to the temperature and pressure of Fe, Zn, and Pb sulfide solubilities points to similarity in chloride speciation, and the neutral species appear to be dominant in the high-temperature region. At 500 degrees C and 1 kbar, the log K D values for FeCl degrees 2 , PbCl degrees 2 , ZnCl degrees 2 , and CuCl degrees are, respectively, -8.76, -9.14, -10.86, and -6.22.

Economic Geology↗

USGS1990

The assemblage WO2 + H2O as a steady-state hydrogen source in moderately reduced hydrothermal experiments

The values of fH2 for the assemblage WO2 + WO2.72 + H2O (designated as WO) have been measured in sealed Au capsules under an external pressure of 2 kbar CH4 and between 650 and 800??C using Ag-AgBr-HBr sensors of fH2. The fH2 values obtained can be represented by the equation log(fWOH2)2kbar,T(??0.06) = (-1924.9 ??(T,K) + 4.06 and are found to be slightly greater than those associated with the previously calibrated C-CH4 buffer. -from Authors

American Mineralogist↗

USGS1986

Effect of pressure on ore mineral solubilities under hydrothermal conditions

Experimental studies were conducted at elevated pressures and temperatures on the combined solubilities of iron, zinc, and lead sulfides in chloride solutions buffered in pH by a silicate assemblage of quartz monzonite composition plus added muscovite, and buffered in/s2 and/o2 by the assemblage pyrite-pyrrhotite-magnetite. Major controls on base metal concentration are temperature, total chloride, and pressure. Higher temperature and higher chloride concentration favor higher metal solubilities as expected, but the pressure effect is opposite to that generally expected and is of considerable importance to the problem of ore mineral transport. At 500 °C, 0.5 kbar, and 1 m total chloride, Fe, Zn, and Pb solubilities were 8500, 4300, and 8700 ppm, respectively, whereas at 1 kbar they were 4200, 2400, and 2600 ppm, and at 2 kbar, 1700, 800, and 1200 ppm. The experimental results thus indicate that the metals could be carried over long distances on a decreasing pressure gradient so long as the temperature decreases were not sufficient to significantly offset the pressure effect. Such a condition could be approximated by a near-adiabatic transport cooling path. Such a condition is probably common geologically, especially for hydrothermal processes involving fairly deep-seated sources of heat and mineral components.

Geology↗

USGS1985

Some mineral stability relations in the system CaO MgO SiO2 H2O HCl

Mineral-aqueous solution equilibria for the assemblages talc-quartz, tremolite-talc-quartz, diopside-tremolite-quartz, wollastonite-diopside-quartz and wollastonite-quartz have been studied at 2 kb total pressure, 500° to 700°C and chloride concentrations from 0.03 to 6.0 molal. Most work was at 1 m chloride. Both buffered and unbuffered data were obtained and a recalibration of the Ag-AgCl buffer is presented. Log equilibrium quotients at 500°, 600° and 700°C are respectively: Ta-Qz ( m MgCl 2 m HCl 2 "> mMgCl2mHCl2 ) 2.57, 1.71, 0.73; Tr-Ta-Qz and Di-Tr-Qz ( m CaCl 2 m MgCl 2 m HCl 2 "> mCaCl2mMgCl2mHCl2 ) 4.98, 3.99, 2.21 and 7.29, 5.30, 3.56; WoDi-Qz ( m CaCl 2 m MgCl 2 "> mCaCl2mMgCl2 ) 3.30, 3.00, 2.79: Wo-Qz ( m CaCl 2 m HCl 2 "> mCaCl2mHCl2 ) 5.15, 3.95, 2.68. Mineral stability fields plotted in terms of these concentration data more tangibly represent the compositional character of real systems and the mass transfer capabilities of their fluids than do the analogous theoretical activity diagrams. Overall dissociation constants of MgCl 2 and CaCl 2 were calculated from the experimental data using the calculated ionic activity constants for the reactions and the established dissociation constants of HCl. The negative log values are respectively: 3.88. 6.63, 9.20 for CaCl 2 and 4.60, 7.54, 10.37 for MgCl 2 at 500°, 600° and 700°C, 2 kb. The Ca values are about an order of magnitude more positive than the conductance-derived values by Frantz and Marshall (1982). The phase relations developed in this study have application to the genesis of talc, tremolite, and diopside-bearing assemblages in some regional metamorphic rocks, but more specifically to the calcsilicate skarn assemblages of many metasomatic aureoles. The equilibrium fluids are characterized by high concentrations of Ca relative to Mg and increasing Ca Mg "> CaMg ratios with decreasing temperatures. The stability fields of talc, tremolite, and quartz expand relative to those of diopside and wollastonite with decreasing temperature, hence their more common appearance as retrograde products in skarn systems.

Geochimica et Cosmochimica Acta↗