Introduction Sample preparation and documentation Components of the system used to study fluid inclusions Magni fyi ng/i11uminati ng system Gas-flow system Electrical system Temperature measurement and recording system Measuring procedures Advantages of system References cited ILLUSTRATIONS Page Q 12 (Figure captions appear on page 13; figures follow on pages 14-18) Figure 1.Photograph showing the components of the system used to analyze fluid inclusions.2. Close-up photograph of the heating/freezing stage.3. Schematic diagram of the air/nitrogen flowcontrol manifold.4. Photograph showing the coils that carry nitrogen gas into the Dewar of liquid nitrogen.5. Photograph showing the tube assembly to prevent frosting on the windows of the stage.TABLE Table 1.Equipment used in the fluid inclusion laboratory AbstractThe supplementary components and operating procedures for the U.S. Geological Survey gas-flow heating/freezing stage have heen developed to enhance the rapid, accurate measurement of fluid inclusions homogenizing between -150°C and FiOn 0 C. Pouhly polished mineral slabs as thick as ?mm are carefully photographed at several magnifications to provide the optimum samples for large-scale growth history-fluid inclusion studies such as those pursued in our laboratory.Long-focal-length condensers and fiber-optic illuminators provide optimal viewing conditions and the large sample chamber volume saves both documentation and samplechangeover time.Nitrogen gas, chilled by passage through a tank of liquid nitrogen, and air, heated by passage through a glass-encased, nichrome-wire heating coil, are used for freezing and heating runs, respectively.Precise control of temperatures and heating rates, as well as careful stage and thermocouple calibration, make it possible to achieve accuracies of +_2.0°C for heating runs and +_0.2°C for freezing runs.The use of gas to control temperature (1) permits rapid accumulation of abundant, accurate data, (2) ameliorates thermal gradient problems so often encountered in stages using convection and/or conduction for heat transfer, and (3) permits the use of a cyclical procedure to measure temperatures that would otherwise be unmeasurable.
Electrochemical laboratory studies of the basic copper salts, malachite (Cu 2 (OH) 2 CO 3 ), brochantite (Cu 4 (OH) 6 SO 4 ), and paratacamite (Cu 4 (OH) 6 Cl 2 ), have been conducted at ambient temperatures and pressures using copper metal-mineral electrodes. The scanning electron microscope showed well-crystallized patinas consisting of crystals usually greater than 2 X 0.5 X 15 mu m for brochantite, 5 X 5 X 5 mu m for paratacamite, and 0.2 X 0.2 X 1 mu m for malachite. Therefore surface energy corrections to calculations of free energy of formation values were not required. The few successfully patinated, copper metal electrodes were titrated with various sulfate, carbonate, and chloride solutions while monitoring the potential between the copper-cupric salt electrode and an Ag-AgCl-KCl reference electrode in an aqueous solution. The observed relationship between electromotive force (emf) and the activity of the titrant permits determination of free energy of formation values for the copper minerals studied. These titrations lead to values of -905.0 and -1341.8 kJ/mole for the free energies of formation (298 degrees C and 1 bar) of malachite and paratacamite, respectively. The recorded changes in emf appear to be a linear function of the log of the activity of the cupric ion in solution, but various junction potentials prevent use of the observed emf values for direct calculation of mineral stabilities. No solid solution between the minerals was observed and the phase changes occurred by partial or complete dissolution of the original phase on the surface of the electrode and precipitation of the new phase. Original textures, at the 100X magnification level, were preserved by the guest minerals.
We present a new method to characterize and quantify groundwater discharge to estuaries and the coastal ocean. Using data from the Pages Creek estuary in the Cape Fear region of southeastern North Carolina, we show that the concentration and carbon isotopic composition (Δ 14 C and Δ 13 C values) of dissolved inorganic carbon (DIC) can provide a tracer of a single, well‐defined component of the surface water‐groundwater system in coastal regions— the integrated freshwater discharge to an estuary from confined aquifers. Groundwater from the two shallowest confined aquifers in the Cape Fear region (the Castle Hayne and the Peedee) has DIC Δ 14 C values ranging from −282‰ to −829‰, significantly lower than the radiocarbon content of surficial (water table) groundwater, rivers and streams, and seawater in the area (Δ 14 C = −38‰ to +97‰). DIC additions from salt marsh decomposition and DIC removal via photosynthesis and gas evasion can influence estuarine DIC concentrations and DIC Δ 13 C values. However, none of these processes results in strongly depleted DIC Δ 14 C values. Because artesian springs are the only significant low‐Δ 14 C DIC input to the Pages Creek estuary, flood‐ebb 14 C budgets provide a direct measure of the fraction of the total freshwater inputs to the Pages Creek estuary that is derived from artesian discharge. With this method, we have observed a striking range in the relative contribution of artesian flow to the Pages Creek estuary freshwater budget. During November 1999 and April 2001 (both periods of low precipitation in southeastern North Carolina), artesian groundwater discharge could account for essentially all of the Pages Creek freshwater inputs. In contrast, during July 2000 (a period of high precipitation in this region), artesian groundwater made a negligible contribution to the creek’s freshwater budget.
Abstract The Eocene‐Oligocene Upper Castle Hayne Aquifer (UCH), a well‐indurated limestone with a very high percentage of secondary moldic porosity, is one of the most productive and extensively developed aquifers in the North Carolina Coastal Plain. Ground water from western wells in the UCH is Ca‐ and HCO 3 ‐rich and ground water from easternmost wells is alkali‐ and Cl‐rich. In general, from west to east across the study area, Sr concentrations [Sr] and isotopic ratios of ground water from the UCH and other aquifers evolve toward those of the host aquifer. At the same well site, water from older aquifers usually has a lower 87 Sr/ 86 Sr ratio than water from younger aquifers, due to interaction between ground water and sedimentary material in the host aquifers. Comparison of 87 Sr/ 86 Sr ratios and [Sr] suggests that most UCH water represents mixing of strontium‐poor recharge water from the Surficial Aquifer with varying amounts of strontium from the aquifer rock. For samples that deviate from the calculated mixing line, strontium ratios can often be used to indicate the source of strontium that did not come from UCH rock. Surface waters are characterized by high 87 Sr/ 86 Sr ratios and variable [Sr] that depend on the proportion of intermixed sea water. Water from the overlying Yorktown and Pungo River aquifers can be recognized by higher 87 Sr/ 86 Sr ratios than those of the UCH and water from the underlying LCH, Beaufort, and Peedee aquifers can be recognized by lower 87 Sr/ 86 Sr ratios and higher [Sr].
