The Relationship between O18/O16 Ratios in Coexisting Quartz, Carbonate, and Iron Oxides from Various Geological Deposits

Analytical techniques for the extraction of oxygen for oxygen isotope analyses involving the high-temperature reduction of minerals with carbon are described. These techniques give reliable results for a few important minerals, including quartz and iron oxides, but give unreliable results for most silicates. Oxygen isotope analyses have been made on naturally occurring and genetically associated carbonates, quartz, and iron oxides. The relationships between the oxygen isotope compositions of the coexisting minerals are consistent with those reasonably expected from known thermodynamic considerations of isotopic fractionation. Relative temperatures inferred from the isotopic data are in excellent agreement with those estimated from other geological evidence. The implications of the oxygen isotope data on the problems of temperature measurements, on the presence or absence of chemical equilibrium between mineral phases, and on the study of isotopic compositions and relative amounts of hydrothermal waters in contact with the minerals are discussed.