Geology topics

John M. Neil

Publications and source records attributed to John M. Neil.

3 recordsLinked to original sources

USGS2014

Vibrational, X-ray absorption, and Mössbauer spectra of sulfate minerals from the weathered massive sulfide deposit at Iron Mountain, California

The Iron Mountain Mine Superfund site in California is a prime example of an acid mine drainage (AMD) system with well developed assemblages of sulfate minerals typical for such settings. Here we present and discuss the vibrational (infrared), X-ray absorption, and Mössbauer spectra of a number of these phases, augmented by spectra of a few synthetic sulfates related to the AMD phases. The minerals and related phases studied in this work are (in order of increasing Fe 2 O 3 /FeO): szomolnokite, rozenite, siderotil, halotrichite, römerite, voltaite, copiapite, monoclinic Fe 2 (SO 4 ) 3 , Fe 2 (SO 4 ) 3 ·5H 2 O, kornelite, coquimbite, Fe(SO 4 )(OH), jarosite and rhomboclase. Fourier transform infrared spectra in the region 750–4000 cm −1 are presented for all studied phases. Position of the FTIR bands is discussed in terms of the vibrations of sulfate ions, hydroxyl groups, and water molecules. Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra were collected for selected samples. The feature of greatest interest is a series of weak pre-edge peaks whose position is determined by the number of bridging oxygen atoms between Fe 3+ octahedra and sulfate tetrahedra. Mössbauer spectra of selected samples were obtained at room temperature and 80 K for ferric minerals jarosite and rhomboclase and mixed ferric–ferrous minerals römerite, voltaite, and copiapite. Values of Fe 2+ /[Fe 2+ + Fe 3+ ] determined by Mössbauer spectroscopy agree well with those determined by wet chemical analysis. The data presented here can be used as standards in spectroscopic work where spectra of well-characterized compounds are required to identify complex mixtures of minerals and related phases.

California↗

USGS1999

Magmatic carbon dioxide emissions at Mammoth Mountain, California

Carbon dioxide (CO 2 ) of magmatic origin is seeping out of the ground in unusual quantities at several locations around the flanks of Mammoth Mountain, a dormant volcano in Eastern California. The most recent volcanic activity on Mammoth Mountain was steam eruptions about 600 years ago, but seismic swarms and long-period earthquakes over the past decade are evidence of an active magmatic system at depth. The CO 2 emission probably began in 1990 but was not recognized until 1994. Seismic swarms and minor ground deformation during 1989, believed to be results of a shallow intrusion of magma beneath Mammoth Mountain, probably triggered the release of C0 1 , which persists in 1998. The CO 2 gas is at ambient temperatures and emanates diffusely from the soil surface rather than flowing from distinct vents. The CO 2 has collected in the soil by displacing air in the pore spaces and reaches concentrations of greater than 95 percent by volume in places. The total area affected by high CO 2 concentrations and high CO 2 flux from the soil surface was estimated at 60 hectares in 1997. Coniferous forest covering about 40 hectares has been killed by high CO 2 , concentrations in the root zone. In more than 300 soil-gas samples collected from depths of 0.5 to 2 m in 1995, CO 2 concentrations ranged from background levels (less than 1 percent) to greater than 95 percent by volume. At 250 locations, CO 2 flux was measured using a closed chamber in 1996; values, in grams per square meter per day, ranged from background (less than 25) to more than 30,000. On the basis of these data, the total emission of magmatic CO 2 , in 1996 is estimated to be about 530 megagrams per day. Concentrations of CO 2 , exceeding Occupational Safety and Health Administration standards have been measured in pits dug in soil and snow, in poorly ventilated buildings, and in below-ground valve-boxes around Mammoth Mountain. CO 2 , concentrations greater than 10 percent in poorly ventilated spaces are not uncommon on some parts of Mammoth Mountain. Humans and other animals exposed to CO 2 concentrations greater than 10 percent could lose consciousness and die rapidly. With knowledge of the problem and reasonable caution, however, the health hazard to humans can be avoided. As noted earlier, the CO 2 emission is related to magmatic activity at depth, but at present (1998) it does not portend an imminent volcanic eruption.

California↗

USGS1991

Geochemical relations and distribution of selected trace elements in ground water of the northern part of the western San Joaquin Valley, California

Water samples were collected from 44 wells in the northern part of the western San Joaquin Valley, California, between March and July 1985 to assess the geochemical relations and distribution of major ions and selected trace-element concentrations in ground water of the area. The ground-waterflow system consists of a semiconfined zone and a confined zone separated by a regionally extensive clay bed. The data show that the areal and vertical distribution of ground-water chemistry in the ground-water-flow system has been affected by different agricultural and natural sources of recharge and the source and redox status of the sediments. Tritium and stable-isotope data indicate extensive infiltration of the semiconfined zone by post-1952 irrigation water originating as runoff from the Sierra Nevada. Tritium concentrations greater than 2 tritium units in most samples from the confined zone indicate that the post-1952 water also has infiltrated to wells completed in this zone. Stable-isotope data indicate that ground water from the semiconfined zone, characterized by the enriched oxygen-18 that is indicative of a Coast Ranges source, occurs in many wells in the confined zone. Movement of water from the semiconfined zone to the confined zone likely is taking place by downward flow through the many wells that perforate the confining clay bed. Trace-element concentrations in the semiconfined and confined zones generally are similar. In contrast, concentrations were significantly different between ground water from Coast Ranges sediments and ground water from Sierra Nevada sediments in both zones. Ground water from Coast Ranges sediments contains significantly higher concentrations of nitrate, boron, and selenium than water from Sierra Nevada sediments. Ground water from Sierra Nevada sediments was significantly higher in arsenic, molybdenum, and manganese than ground water from Coast Ranges sediments. These differences result from a combination of variable availability of the constituents and redox controls on mobility. Selenium, the only priority pollutant to exceed the U.S. Environmental Protection Agency's drinking-water standard, equaled or exceeded the standard of 10 micrograms per liter in water from two wells completed in the semiconfined zone and one well in the confined zone. The conservative nature of selenium behavior in the oxidized Coast Ranges deposits is shown by the high correlation (r=0.88) between selenium concentrations and specific conductance in water from these deposits in the semiconfined zone. High selenium concentrations in both zones are spatially related to the location of Coast Ranges streams that have high selenium concentrations and that were historical sources of recharge to the zones. Principal-component analysis confirmed the association of boron, chromium, lithium, and selenium, and the association of arsenic, iron, manganese, and molybdenum to sediments in the study area. The analysis indicated that the first group is associated with Coast Ranges sediments and the second with Sierra Nevada sediments.

Water Supply Paper↗