Geologic sections of Iron Mountain (part 2): Supplement 3 from 'Geology and mineralization connected with the intrusion of a quartz monzonite porphyry, Iron Mountain, Iron Springs district, Utah' (Thesis)

Iron Mountain is one of three intrusive bodies exposed in the Iron Springs district approximately 15 miles west of Cedar City, Utah. It is the erosional remnant of a quartz monzonite porphyry, intruded into Mesozoic limestone and clastic rocks probably at a depth of less than one mile. The quartz monzonite was intruded in large part along the base of the Carmel formation and has pushed aside the overlying sedimentary rocks as if they were a trap-door hinged on the southeast. Metamorphism is very weak and is confined for the most part to the Sandy member at the base of the Carmel formation. The Homestake limestone member of the Carmel formation is locally replaced by massive bodies of iron ore, consisting chiefly of magnetite, specularite, carbonates and phlogopite. The mineralization is associated with the quartz monzonite but was not necessarily derived from it. Chemical analyses and the mineralogy of the limestone and the ore show that Ca and CO2 have been removed and important amounts of Fe, Si, Mg, Al and K have been added with no change in volume during replacement of the limestone. A high temperature and a low confining pressure during mineralization may have permitted the transport of iron halide in a gas phase, but the addition of some of the other constituents and the removal of Ca are not easily accounted for by such a mechanism.