ORE TEXTURAL STUDIES AND ORIGIN OF THE PILOT KNOB HEMATITE DEPOSIT, IRON CO., MO

Since 1815 the origin of Pilot Knob Hematite Deposit located in Iron County, Missouri has been under debate. The deposit has been suggested to be either of hydrothermal or of sedimentary origin by various authors. The hydrothermal hypothesis states that the deposit is related to the 1400-1500 mya Proterozoic igneous activity of the St. Francois Mountains Terrane. The other hypothesis seems to be gaining more acceptance in the geological community and states that the deposit is of sedimentary origin as a Proterozoic sedimentary banded iron formation.

This research project was designed to investigate the mineralogy and ore textures of the Pilot Knob Hematite deposit to give insight into its origin. Specimens from Pilot Knob were made into polished sections and then studied under a reflecting petrographic microscope. Though oolites have been found in very similar laminated hematite ores from the nearby Cedar Hill deposit (Dudley and Nold, 2002), no oolites were found at Pilot Knob. The hematite was deposited in very fine-grained distinct laminae, indicating sedimentary origin. Euhedral hematite is common in these samples. There seems to be little remoblization of hematite or replacement of intercalated tuffaceous sedimentary grains. Even though no oolitic laminae were found that would indicate that Pilot Knob is definitely of sedimentary origin, the laminated nature of the ores and the extreme similarity to other banded iron formations of undoubted sedimentary origin leads to the conclusion that sedimentary origin is likely.