THE MISSOURI PROTEROZOIC IRON METALLOGENIC PROVINCE—THE TYPES OF DEPOSITS AND THEIR GENETIC RELATIONSHIPS

The Iron Metallogenic Province of the Missouri USA Proterozoic St. Francois Mountains Terrane contains four distinct but genetically related types of deposits: 1) magnetite-hematite deposits which have crystallized from an iron oxide magma and from hydrothermal solutions, and similar in some aspects to “Kiruna-type” deposits, 2) iron oxide-copper-gold (IOCG) deposits, 3) steeply dipping hydrothermal magnetite-hematite vein deposits, 4) sedimentary hematite iron formation deposits that have originated from exhalations into caldera lakes. Deposits to be discussed within this study are as follows: 1) magmatic/hydrothermal deposits--Pilot Knob magnetite, Iron Mountain, Pea Ridge, and Kratz Spring, 2) iron oxide-copper-gold (IOCG) deposits--Boss-Bixby, Bourbon, and Camels Hump, 3) hydrothermal vein deposits--Shepherd Mountain, Shut-Ins, and Hogan, 4) sedimentary iron formation deposits--Pilot Knob hematite, Cedar Hill, College Hill, Cuthbertson Mountain, and Russell Mountain. Mineralogical and textural features which indicate that portions of the “Kiruna-type” deposits originated from crystallization of an iron oxide magma include, 1) magnetite and hematite phenocrysts, some of which are zoned (PKM, PR), 2) albitic plagioclase being the most abundant gangue mineral, some of which is trachytic (PKM), 3) finer-grained ores near contacts, interpreted as chill zones (PKM), and 4) dendritic magnetite textures (PKM). Leakages of hydrothermal fluids from the magmatic/hydrothermal deposits developing at depth resulted in steeply dipping magnetite-hematite veins that represent part of the plumbing system which ultimately vented as hot springs into caldera lakes. The laminated hematite iron formations described herein, some of which have previously been described as being of hydrothermal replacement origin, contain features which indicate that they are of undoubted sedimentary origin, such as ripple marks, mud cracks, and oolitic textures. These hematite iron formations were all deposited in caldera lakes within or near the boundaries of the Taum Sauk caldera.