Two or more minerals in the group magnetite, hematite, pyrite, siderite, and graphite of apparent diagenetic or low-grade metamorphic origin coexist in late Precambrian sub-graywackes in northern Utah. If equilibrium was approached between these minerals and the pore fluid during diagenesis (25 ± 25°C) and again during metamorphism (400 ± 100°C), thermodynamic calculations indicate the following increases in oxygen, carbon dioxide, and sulfur fugacities during low-grade metamorphism (expressed in orders of magnitude): f02, 35–70; fco2, 0–9; fs2, 20–45. Progressive disappearance of siderite and appearance of hematite as a function of metamorphic grade suggest that oxidation accompanied metamorphism.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.