CONSTRAINING 500 MILLION YEARS OF FLUID-ROCK INTERACTIONS, LOWER ORDOVICIAN KNOX GROUP, TENNESSEE-KENTUCKY

Lower Ordovician Knox Group carbonates share common depositional and diagenetic characteristics throughout the southern Appalachians and into the continental interior of North America. Extensive breccia networks linked to exposure-related subsurface solution locally serve as petroleum reservoirs and host stratabound zinc and related Mississippi Valley type ore zones. Four mining districts as well as former exploration programs in Tennessee-Kentucky provide regional geologic information and three-dimensional sample suites to assess porosity and cementation histories over a >50,000 km² area. Although the breccia bodies are broadly similar over large areas, the cement assemblage, sequence of pore filling, and remaining porosity vary considerably. Numerous studies have developed cementation sequences for local or regional breccias that indicate considerable spatial and temporal variation in the mineralizing brine systems. Only localized areas have commercially significant amounts of sulfide minerals; most late breccias are cemented by carbonate gangue with varying amounts of remaining porosity. Hydrothermal dolomite (± quartz) cement predates sulfide mineralization in central Tennessee, whereas dolomite forms before and after sulfide precipitation in east Tennessee and southern Kentucky breccias. Fluorite and barite dominate the Sweetwater breccia cements, and local areas of central Tennessee, but are typically absent elsewhere. MVT mineralization in eastern Tennessee appears to be related to basinal brine migration linked to late Paleozoic orogenic events, but appears to be younger in Central Tennessee. Although much work remains, evolving chronologic and other genetic constraints suggest localized brine transport and mineral precipitation throughout the Phanerozoic with distinct differences within the region.