New evidence on magnetite oxygen isotope geothermometers at 175° and 112°C in Wairakei steam pipelines (New Zealand)

Abstract

Millimeter deep surface layers of magnetite occur in the steam pipelines of the Wairakei geothermal power station as part of serious corrosion discovered after 15 years of service. These quasi-experimental growths provide the following oxygen isotope calibration points of magnetite and H 2O below the previously available experimental range: Δ(175°C) = −7.9 ± 0.5 and Δ(112°C) =−3.7 ± 0.5 The data support the earliest proposed magnetite−H 2O fractionation curve, by J.R. O’Neil and R.N. Clayton, with an isotopic “cross-over” near 50°C, and could indicate a relatively low-temperature origin for some Precambrian iron formations.