/sup 18/O relations in alunite minerals: potential single-mineral thermometer
The alunite group of minerals are hydrous sulfates (alunite: KAl/sub 3/(SO/sub 4/)/sub 2/(OH)/sub 6/) that occur in altered felsic rocks and are often associated with epithermal gold-silver mineralization. The equilibrium oxygen isotope fractionation between the sulfate and hydroxyl groups is temperature dependent. Thus, if natural alunites form in internal isotopic equilibrium, they provide a pressure-independent, single-mineral thermometer. Alunite and BaSO/sub 4/ were analyzed by reaction with ClF/sub 3/ at 500/sup 0/C. Based on analyses of BaSO/sub 4/, and mixtures of BaSO/sub 4/ and Al(OH)/sub 3/, fractionation factors of 15.8 and 7.9 per thousands were determined for ..delta../sup 18/O (SO/sub 2/-O/sub 2/) and delta/sup 18/(BaSO/sub 4/-O/sub 2/), respectively. With this information, the delta/sup 18/O values of sulfate and hydroxyl groups in alunite can be determined. delta/sup 18/O (SO/sub 4/-OH) determined for a suite of natural alunites formed under a variety of conditions at Goldfield, Nevada, range from -3.5 to +5.1 and correlate with delta/sup 18/O values of 3.3 to 6.0 per thousands, deltaD values of -155 to -73 per thousands, and previously published delta/sup 34/S values of -1.8 to + 17.0 per thousands. Synthesis and exchange experiments, as well as fluid inclusions measurements of natural samples, are being conducted in an attempt to determine the degree to which internal isotopic equilibrium is established in natural alunites and to calibrate an alunite geothermometer. In addition to theoretical significance, such determinations are useful for geothermometry and in distinguishing between hypogene and supergene origins of this group of minerals.
- Research Organization:
- Geological Survey, Menlo Park, CA (USA)
- OSTI ID:
- 6326809
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
152004* -- Geothermal Data & Theory-- Isotope & Trace Element Studies
58 GEOSCIENCES
580400 -- Geochemistry-- (-1989)
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SULFATES
ALUNITE
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHEMISTRY
ENERGY SYSTEMS
EQUILIBRIUM
EVEN-EVEN NUCLEI
FEDERAL REGION IX
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOTHERMAL SYSTEMS
GEOTHERMOMETERS
GEOTHERMOMETRY
GOLD ORES
HYDROTHERMAL SYSTEMS
INCLUSIONS
ISOTOPE RATIO
ISOTOPES
KINETICS
LIGHT NUCLEI
MEASURING INSTRUMENTS
MINERALIZATION
MINERALS
NEVADA
NORTH AMERICA
NUCLEI
ORES
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
POTASSIUM COMPOUNDS
POTASSIUM SULFATES
REACTION KINETICS
ROCK-FLUID INTERACTIONS
SILVER ORES
STABLE ISOTOPES
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
TEMPERATURE MEASUREMENT
THERMOMETERS
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