Oxygen isotope variations in goethite

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6031530

Yapp, C J

Room temperature treatment of fine-grained, synthetic goethite samples with bromine pentafluoride at low pressures (ca. 0.07 bars) was found to remove nonstoichiometric water without seeming to remove any structural oxygen. Subsequent reaction between treated goethite and excess bromine pentafluoride at 500/degree/C produced stoichiometric oxygen yields and /delta//sup 18/O values with a reproducibility of better than /plus minus/ 0.2 per mil. Similar success was achieved with finely ground natural samples. Analyses of natural goethites from a wide variety of locales revealed a total /delta//sup 18/O range of greater than 16 per mil (- 9.5 to + 6.8). There is a general correspondence between the /delta//sup 18/O values of these goethites and the /delta//sup 18/O values of the associated modern waters. A marine goethite has the most positive /delta//sup 18/O value, while continental goethite /delta//sup 18/O values are more negative. Data from marine goethite and manganite samples suggest that there could be a substituent cation effect on the mineral-water /alpha/-18 value. A plot of the corresponding /delta/D and /delta//sup 18/O values from natural goethites yields a data array which is approximately parallel to the meteoric water line. Preliminary data on goethites synthesized at 55/degree/C indicate that the goethite-water /alpha/-18 may be temperature dependent. Proper calibration of any temperature dependency would enable the presumed equilibrium isotopic exchange temperature of natural goethites to be determined directly from the /delta/D vs /delta//sup 18/O diagram. Thus, these goethite lines may play a role in low temperature geochemistry that is analogous to that of the kaolinite line.

• Research Organization: Univ. of New Mexico, Albuquerque (USA)
• OSTI ID: 6031530
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300 -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400* -- Geochemistry-- (-1989)
BROMINE COMPOUNDS
BROMINE FLUORIDES
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHEMISTRY
COMPARATIVE EVALUATIONS
CONNATE WATER
EQUILIBRIUM
FLUORIDES
FLUORINE COMPOUNDS
GEOCHEMISTRY
GOETHITE
GROUND WATER
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
INTERSTITIAL WATER
ION EXCHANGE
ISOTOPE RATIO
ISOTOPES
KINETICS
MINERALIZATION
MINERALS
OXIDE MINERALS
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
REACTION KINETICS
STOICHIOMETRY
STRUCTURAL CHEMICAL ANALYSIS
TEMPERATURE EFFECTS
VARIATIONS
WATER