ILLITE PRECIPITATION AT JACK BRADLEY CAVE (PULASKI COUNTY, KENTUCKY) AS A RESULT OF ACID MINE DRAINAGE

Jack Bradley Cave (Pulaski County, Kentucky) formed in the Newman Limestone underlying the coal-bearing Pennington Formation. Mountain-top strip mining is common in the Pennington Formation in Pulaski County and surrounding areas of southern Kentucky, while caves are common in the underlying Newman Limestone. Karst drainage in the Newman Limestone is an important aspect of the aquifer system in this region, and interactions with the overlying strip mines can have a significant impact.

A major feature of Jack Bradley Cave is a 65 foot dome that drains from a mountain-top strip mine above the cave. Coatings on the surface of the dome, and extending down the stream in the cave, were analyzed using x-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) and are extensive deposits of black poorly crystalline manganese oxides as well as an unusual white precipitant of illite clay.

Chemical experiments to reconstruct the processes at Jack Bradley Cave involved leaching surface soil from the cave area with sulfuric acid and analyzing the resulting precipitant. The results of these experiments suggest that sulfuric acid as a result of acid mine drainage from the strip mine is leaching aluminum from clays in the soil at the surface. As it drains through the limestone, the chemical conditions change, causing the illite to reprecipitate. The illite creates a surface coating on the walls of the cave that prevents further interaction with the cave walls and the water remains acidic (pH = 4) within the dome of the cave.