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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.

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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.

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