Compositional Variation in Component Layers in Natural Illite/Smectite
Published chemical data for suites of mixed-layer minerals from diagenetic sedimentary rocks, hydrothermally altered tufts, and a metasomatic bentonite bed indicate that the layer charge and composition of the different components of illite/smectite (I/S) differ from one geological environment to another. It appears that the composition of the elemental smectite and illite layers in the I/S is more or less constant for samples within each geologic setting. In the examples considered, the smectite layers are predominantly montmorillonitic in character (i.e., the charge is in the octahedral site), whereas the illite layers show different types of charge sites, depending upon the suite studied. Illite layers appear to have about the same charge in all three suites studied, slightly more than 0.7 per O10(OH)2 unit, whereas the smectite layers in the different suites range in charge from about 0.3 to 0.7 per O10(OH)2 unit. Cation-exchange capacities reflect these differences in charge, although not ideally. The differences in the composition of the component layers in each geologic suite of mixed-layer clays are probably due either to differences in the bulk chemistry of the rocks in the different suites or to differences in intensive variables, such as temperature and pressure, of the regime under which they have formed.
Hydrothermal rock alteration at Wairakei, New Zealand
Petrographic examination of drill cores demonstrates that the flat-lying tuffaceous and arenaceous rocks of the Wairakei hot spring area, central North Island, New Zealand, have been and are still being altered by hydrothermal solutions. Interbedded argillaceous rocks remain unaltered. Alteration is progressive with depth and comprises a surficial zone of sulfuric acid leaching and zones of argillization, zeolitization, and feldspathization. The presence of an underlying zone of primary acid leaching extending down to the interface of the magmatic emanations is inferred.
The Geology and Ground-Water Resources of Calcasieu Parish Louisiana
Large quantities of fresh ground water are available in Calcasieu Parish. Fresh water is present in sand of Recent, Pleistocene, Pliocene, and Miocene ages, although locally only small supplies for rural or stock use can be obtained from the shallow sand lenses of Recent and Pleistocene ages. The principal fresh-water-bearing sands are the "200-foot," "500-foot," and "700-foot" sands of the Chicot aquifer of Pleistocene age, from which 105 million gallons is pumped daily. A yield of as much as 4,500 gpm (gallons per minute) has been obtained from a single well. The sands are typical of the Chicot aquifer throughout southwestern Louisiana in that generally they grade from fine sand at the top to coarse sand and gravel at the base of the aquifer. The coefficient of permeability of the principal sands in Calcasieu Parish ranges from 660 to about 2,000 gpd (gallons per day) per square foot and averages 1,200 gpd per square foot. The permeability of the sands generally varies with textural changes. The maximum depth of occurrence of fresh ground water in Calcasieu Parish ranges from about 700 feet to 2,500 feet below mean sea level; locally, however, where the sands overlie structures associated with oil fields, the maximum depth is less than 300 feet. Pumping has caused water levels to decline, at varying rates, hi all the sands. In the "200-foot" sand they are declining at a rate of about 2 feet per year. In the industrial district of Calcasieu Parish, levels in the "500-foot" sand are declining at a rate of about 5 feet per year, and in the "700-foot" sand at a rate of about 3.5 feet per year. Salt-water contamination is accompanying the water-level decline in the "700-foot" sand in the central part of the parish. Quality-of-water data indicate that water from wells screened in the Chicot aquifer generally is suitable for some uses without treatment but would require treatment to be satisfactory for other uses. The temperature of the water ranges from 70° to 79°P. The lenticular sands of Pliocene and Miocene ages have not been used as a source of fresh ground water in Calcasieu Parish; however, north of the Houston River these formations contain fresh water, and the water contained In these formations in other parts of southwestern Louisiana is known to be soft and suitable for most purposes. 2 GEOLOGY AND GROUND WATER, CALCASIEU PARISH, LA.