SILICIFICATION HISTORY OF THE BOONE FORMATION (LOWER MISSISSIPPIAN), SOUTHERN OZARK REGION, AND ITS RELATIONSHIP TO THE OUACHITA OROGENY

Silicification history of the Boone Formation, Osagean Series (Lower Mississippian), can be divided into four periods: 1) penecontemporaneous chert formation beneath the sediment-water interface by silica gel produced from volcanic ash during maximum flooding; 2) later diagenetic chert formation as a post-depositional, silica-bearing groundwater replacement of upper Boone limestones along bedding planes during highstand-regression, producing an apparently interbedded limestone-chert sequence; 3) hydrothermal, post-depositional, silica replacement of highstand calcisiltites at the base of the upper Boone, much like a confined aquifer system, leaving disseminated carbonate within the silica that was removed eventually by groundwater producing tripolitic chert; 4) a second pulse of hydrothermal silica-bearing fluids moving through the tripolitized interval leaving terminated and doubly terminated quartz crystal druse in the cavities of the tripolitic chert.

Lead-zinc mineralization in both the Boone and older formations is well developed on the flanks of the Ozark Dome, and became known as the Mississippi Valley type deposits, with designated production as the Central Missouri district, Northern Arkansas district, Tri-State district, and the Viburnum Trend. That exploitation began as early as 1742, but significant mining began with the incorporation of the St. Joe Lead Company in 1864. This mineralization is immediately north of the Ouachita orogenic belt and likely reflects hydrothermal movement into the Lower Mississippian and older strata produced by the Ouachita Orogeny during the Pennsylvanian Period.