Iron partitioning in oil shale of the Green River Formation, Colorado: A preliminary Mössbauer study

Abstract

Oil shale of the Green River Formation (Eocene) in the Piceance Creek Basin, Colorado contains seven major iron-bearing minerals: pyrite, marcasite, pyrrhotite, Mg-siderite, Fe-dolomite, ankerite and Ca-ankerite. Only recently have workers recognized that these rocks contain large quantities of iron-bearing carbonate minerals. Preliminary Mössbauer spectroscopy analysis of four oil-shale and two marlstone samples from the Green River Formation shows that the dominant iron-bearing compound is usually an iron-carbonate mineral, generally Ca-ankerite or Fe-dolomite. The second most abundant iron-bearing phase is an iron sulphide, generally pyrite. In the samples studied, the iron partitioning is variable between the carbonate and sulphide phases. Lower grades of oil shale and marlstone also have an iron-bearing silicate phase, which is perhaps an iron-bearing phyllosilicate, possibly chlorite.