Mid-Continent Section

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Significance of Carboniferous Terminated and Doubly-Terminated Quartz Crystals, Southern Ozarks


L. G. Henbest (1945, 1968) described unusual, doubly terminated, quartz overgrowths that had formed on the quartz sand nuclei of ooliths from limestones in both the Hale (Prairie Grove Member) and Bloyd (Brentwood Member) Formations (Morrowan Series, Pennsylvanian Subsystem) in northwestern Arkansas and northeastern Oklahoma. These overgrowths extend into the oolith cortex by replacement. Subsequent study has documented similar occurrences in oolitic strata as old as Lower Mississippian - Short Creek Oolite, upper Boone Formation (Osagean), and higher in the Morrowan section - Kessler Member, Bloyd Formation. In addition, on-going studies of tripolitic chert formation in the upper Boone Formation have discovered abundant, terminated quartz crystal druse that fills vugs produced by decalcitization of the later diagenetic chert host rock in northwestern Arkansas and southwestern Missouri. It appears that this quartz represents the distal effects of the geothermal event that produced the abundant, quartz crystals that fill veins in Paleozoic strata forming a belt across the central Ouachita Mountains. This thermal event likely emplaced the lead and zinc deposits of the famous Picher district, Oklahoma and Kansas, as well as lesser deposits across northern Arkansas. Dating these deposits has been equivocal, but it seems to reflect lateral secretion from the Ouachita Orogeny, and thus, represents a late Paleozoic, probably late Pennsylvanian, event.